CN106383221A - Stratum stress sensitive experiment testing method and device - Google Patents

Abstract

The invention provides a test method and device for a stratum stress sensitivity experiment. The method comprises the following steps: (1) obtaining actual geological data; (2) selecting a formula for calculating the pressure arch ratio of the reservoir according to the shape of the reservoir and the difference in mechanical properties between the reservoir and surrounding rock; (3) determining the The initial formation pressure and initial overlying pressure of the rock; (4) Determine the relationship between the confining pressure and the displacement pressure and the back pressure; (5) Restore the core without natural fractures to the original irreducible water saturation; (6) ) aging treatment of the core; (7) restoring the original stress and fluid pressure of the core; (8) simulating the stress sensitivity of the reservoir during the mining process; (9) data processing and analysis. According to the actual geological data of the oil and gas reservoir, the invention can obtain the quantitative change relationship between the overlying pressure of the reservoir and the pore pressure during the development of the oil and gas reservoir.

Description

A test method and device for stratum stress sensitivity experiment

technical field

The invention relates to the field of oil exploitation, in particular to a test method and device for stratum stress sensitivity experiments.

Background technique

The reserves of low-permeability and ultra-low-permeability oil and gas fields account for a relatively large proportion of my country's undeveloped petroleum geological reserves, and they are the resource base for my country's petroleum industry to increase reserves and production. Their reasonable and effective development plays a vital role in the development of my country's petroleum industry . To rationally develop low-permeability reservoirs, it is an important prerequisite to understand the particularity of low-permeability reservoirs in development.

For deeply buried oil and gas reservoirs, the reservoir rocks are simultaneously affected by the overlying strata pressure, surrounding lateral pressure, and pore fluid pressure. Before the oil and gas reservoirs are developed, the stress system is in a balanced state. However, in the process of oilfield development, due to the shortage of underground materials or the release of in-situ stress, the pressure of formation pore fluid decreases, the effective stress on the rock skeleton increases, and the rock skeleton deforms, which changes the physical parameters of the rock such as permeability and porosity. The phenomenon that the physical properties of the reservoir change due to the change of the stress field is called the stress sensitivity effect. A large number of studies at home and abroad have shown that low-permeability reservoirs have strong stress-sensitivity effects. Stress sensitivity has an important impact on well pattern deployment, production differential pressure, oil and gas well proration, and ultimate recovery. Therefore, it is of great practical significance to find out the influence of stress sensitivity of low-permeability reservoirs on the development of low-permeability oilfields and its influence mode.

The stress sensitivity of reservoirs is generally studied through laboratory experiments. Most of the current experimental methods are carried out with reference to the industry standard "reservoir sensitivity flow test evaluation method", and the stress sensitivity of the reservoir is evaluated according to this standard. In terms of experimental stress loading, the current stress sensitivity experiments are all based on the overlying rock gravity acting on the reservoir to study the stress sensitivity effect of the reservoir. In fact, in the process of oil and gas production, the pressure of the overlying strata in the reservoir is not constant. The pore fluid pressure in the reservoir has a large pressure drop near the wellbore and a small pressure drop far away from the wellbore, and is basically funnel-shaped. Inhomogeneous deformation occurs, and the overlying strata will produce a pressure arch effect. The pressure arch effect allows the gravity of the overlying strata carried by the reservoir rock to transfer to the strata outside the pressure arch along the principal stress direction, reducing the overlying pressure acting on the reservoir. The current stress-sensitivity experiments based on the constant overburden pressure of the reservoir cannot reflect the real stress path of the reservoir rock during oil and gas production. Therefore, it is of great significance to establish a set of stress-sensitivity experimental methods in which overburden pressure and pore pressure change simultaneously, and to design a set of matching experimental devices accordingly.

According to the experimental loading stress conditions, the current stress sensitivity experiments can be mainly divided into confining pressure stress sensitivity experiments and internal pressure stress sensitivity experiments. Both methods are uniaxial strain experiments, that is, it is considered that the reservoir rock only has vertical strain under in-situ stress conditions, and there is no strain in the horizontal direction. In addition, both methods assume that the pressure of the overlying strata of the reservoir is constant, and the vertical effective stress of the reservoir increases linearly with the decrease of the pore pressure of the reservoir. In the experiment, the confining pressure is increased and the confining pressure , decreasing the pore pressure to simulate a linear increase in effective stress.

(1) Stress sensitivity test method with variable confining pressure and constant internal pressure

The method of variable confining pressure and constant internal pressure is a traditional stress-sensitive experimental testing method. This method converts the decrease of reservoir pore pressure into the increase of confining pressure through effective stress during the actual production of oil and gas reservoirs, ensuring that the effective stress on the core during the experiment of variable confining pressure and constant internal pressure is equivalent to that during the process of oil and gas production. Effective stress during pore pressure drop. The variable confining pressure stress sensitivity test refers to "SY/T5358-2002 Reservoir Sensitivity Flow Test Evaluation Method", the test method is simple, easy to operate and control.

In 2011, Jiao Chunyan used the Auto-floodTM (AFS300TM) flooding evaluation system provided by the American Core Company to evaluate the stress sensitivity of the full-diameter core of the Triassic ultra-low permeability outcrop in the Ordos Basin under variable confining pressure and constant internal pressure. The system includes an automatic pressure control system and an automatic data acquisition system. The back pressure system and confining pressure system are controlled by high-precision multi-stage plunger displacement pumps in constant pressure mode. The injection displacement system can be set to the constant flow rate or constant pressure displacement mode according to the experimental requirements. In order to more accurately collect the differential pressure at both ends of the core, the laboratory uses three high linear differential pressure sensors with different ranges.

The experimental process of this method is as follows: ①Dry the core at constant temperature for 48 hours, measure the length, diameter and gas permeability of the core; 4. Pressurize the core, increase the confining pressure to 8.97MPa, increase the pressure by 3.45MPa each time, increase the back pressure to 3.45MPa, and keep it unchanged; 5. Open the valve of the intermediate container for kerosene , carry out the kerosene single-phase seepage experiment, record the pressure difference and flow rate of the core under different pressure differences, and calculate the liquid phase permeability under the effective stress through the slope of the regression line; ⑥ gradually increase the confining pressure and repeat step ⑤ until The confining pressure rises to 37.93MPa, the pressure is relieved, the pump is stopped, and the experiment ends.

The disadvantages of this experimental method and experimental device are: the core stress change path used in the experiment does not conform to the actual situation of fluid pressure reduction in the actual development of oil and gas fields; The gap of the rubber sleeve of the holder has a great influence on the experimental results; since the injection system only has a high-pressure liquid cylinder and no high-pressure gas source, the device can only simulate the seepage of single-phase liquid in the reservoir, and the influence of the gas phase cannot be considered; due to the lack of The constant temperature box, the device cannot simulate the temperature conditions of the original reservoir.

(2) Stress sensitivity test method with variable internal pressure and constant confining pressure

The traditional experimental test of variable confining pressure and constant internal pressure does not conform to the actual situation that the fluid pressure becomes smaller in the actual development of oil and gas fields. In recent years, scholars have proposed the method of changing internal pressure and constant external pressure. Although this method is relatively complicated and difficult to operate, it can better simulate the development process of oil and gas reservoirs, and thus can obtain more reliable experimental results.

In 2015, Gao Tao conducted a stress sensitivity experiment on the core of block X by using the experimental test method of the internal pressure of the confined pressure drop. In this experiment, a back pressure valve was added at the outlet end of the core, the outlet pressure was controlled by the back pressure valve, the inlet pressure was controlled by an air compressor pump, and the pressure difference between the displacement pressure and the back pressure was controlled (maintaining the confining pressure constant) to simulate the change of pore pressure, and then determine the change law of permeability with effective stress. The experiment is carried out in a constant temperature box, which can simulate the actual reservoir temperature conditions. Using the ring pressure pump to control the confining pressure can make the confining pressure change synchronously with the change of the back pressure during the pressurization process.

The experimental process of this method is as follows: ①Dry the core at constant temperature for 48 hours, measure the length, diameter and gas permeability of the core; Through the process, zero the initial value of the instrument; ④ age the core; ⑤ pressurize the core to ensure that the confining pressure is greater than 5.0 MPa of the pore pressure, and slowly increase the pore pressure and confining pressure synchronously in the ring pressure tracking mode until the pore pressure Increase to 30MPa, and increase the confining pressure to 40MPa; ⑥Set the confining pressure to a constant pressure mode during the experiment, that is, keep the confining pressure at 40MPa, and gradually decrease the internal pressure with a step of 3.0MPa. Each test is stabilized after 2 hours , record the pressure difference and flow rate of the core under different pressure differences, and calculate the liquid phase permeability under the effective stress through the slope of the regression line; Press down, stop the pump, and the experiment is over.

The disadvantages of this experimental method and experimental device are: the core stress change path used in the experiment does not conform to the actual situation that the fluid pressure decreases during the actual development of the oil and gas field, and the pressure of the overlying strata decreases accordingly; Controlling the displacement pressure difference with the back pressure, the stability of the displacement pressure difference is poor, and the experimental operation is more difficult. If the experimental medium is gas, it will be affected by a certain slippage effect.

Contents of the invention

One object of the present invention is to provide a kind of stratum stress sensitivity experimental testing method; This method is a kind of stress sensitive experimental testing method that the reservoir overlying pressure and pore pressure change simultaneously in the process of simulating oil and gas reservoir development;

According to the actual geological data of oil and gas reservoirs, this test method can obtain the quantitative change relationship between the overburden pressure of the reservoir and the pore pressure, and can eliminate the micro-fractures opened during the core sampling process and the gap between the rubber sleeve of the core holder in the experiment. Impact. The designed experimental device can realize the function of simulating the mining process, changing the confining pressure and internal pressure synchronously, and can solve the problem of poor stability of displacement pressure difference in the experiment. The experimental method and device can study the stress sensitivity characteristics of the reservoir under the real stress change path during the development of the oil and gas reservoir.

Another object of the present invention is to provide an experimental testing device for formation stress sensitivity.

In order to achieve the above object, on the one hand, the present invention provides a kind of stratum stress sensitivity test method, wherein, said method comprises the following steps:

(1) Obtain actual geological data;

(2) According to the shape of the reservoir and the difference in mechanical properties between the reservoir and the surrounding rock, select the formula for calculating the pressure-arch ratio of the reservoir; when the shear modulus ratio between the reservoir and the surrounding rock is between 0.8-1.2, select inclusions theory, otherwise choose heterogeneity theory;

(3) Determine the initial formation pressure and initial overlying pressure of the reservoir rock;

(4) Determine the relationship between confining pressure and displacement pressure with back pressure;

(5) recover the obtained rock core with no natural fractures to the original irreducible water saturation;

(6) carry out aging treatment to rock core;

(7) Restoring the original stress and fluid pressure of the rock core;

(8) Simulate the stress sensitivity of the reservoir during the mining process;

(9) Data processing and analysis.

According to some specific embodiments of the present invention, the geological data at least includes the shape of the reservoir and the difference in mechanical properties between the reservoir and the surrounding rock.

According to some specific embodiments of the present invention, wherein, the geological data further includes reservoir aspect ratio, depth parameter, shear modulus ratio, reservoir Poisson's ratio, non-reservoir Poisson's ratio, reservoir depth, reservoir A combination of one or more of width, reservoir thickness, reservoir rock density, porosity, and Biot consolidation coefficient.

In step (2), those skilled in the art can select the corresponding formula for calculating the pressure arch ratio of the reservoir according to the shape of the reservoir and the difference in mechanical properties between the reservoir and the surrounding rock. For example, it can be selected according to the following table:

Table 1 Calculation method of pressure arch ratio of reservoirs with different shapes

In the table, γ, pressure arch ratio; e, reservoir aspect ratio; υ, reservoir Poisson's ratio; υ*non-reservoir Poisson's ratio; R _μ , shear modulus ratio.

In step (3), those skilled in the art can determine the initial formation pressure p ₀ and the initial overlying pressure σ ₀ of the reservoir rock according to existing methods; and according to some specific embodiments of the present invention, wherein:

The initial formation pressure _p0 of reservoir rock can be calculated according to the hydrostatic pressure gradient, and the calculation formula is:

p ₀ =ρ _l hg (1)

In the formula, ρ _l is the density of pore fluid, in g/cm ³ ; h is the buried depth of the reservoir, in km; g is the acceleration of gravity, in 9.8m/s ² .

The initial overlying pressure σ ₀ refers to the pressure generated by the total weight of the rock skeleton and pore fluid in the overlying strata, which can be expressed as:

${\mathrm{<span\; class="notranslate">\; \&sigma;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; =</span>{<span\; class="notranslate">\; \&Integral;</span>}_{\mathrm{<span\; class="notranslate">\; 0</span>}}^{\mathrm{<span\; class="notranslate">\; z</span>}}<span\; class="notranslate">\; \{</span><span\; class="notranslate">\; \&lsqb;</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; \&phi;</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; z</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&rsqb;</span>{\mathrm{<span\; class="notranslate">\; \&rho;</span>}}_{\mathrm{<span\; class="notranslate">\; G</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; z</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; \&phi;</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; z</span>}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; \&rho;</span>}}_{\mathrm{<span\; class="notranslate">\; f</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; z</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \}</span>\mathrm{<span\; class="notranslate">\; g</span>}\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; z</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>$

In the formula, z is the depth of the target layer, in m; φ(z) is the porosity at depth z; ρ _G (z) is the rock skeleton density at depth z, in kg/m ³ ; ρ _f (z) is Pore fluid density at depth z, unit kg/m ³ .

In step (4), those skilled in the art can determine the variation relationship of confining pressure and displacement pressure with back pressure according to existing methods; and according to some specific embodiments of the present invention, wherein:

The relationship between confining pressure σ and back pressure can be expressed by formula (3):

$\mathrm{<span\; class="notranslate">\; \&sigma;</span>}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; \&sigma;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; \&gamma;\&alpha;p</span>}}_{\mathrm{<span\; class="notranslate">\; h</span>}}<span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; \&gamma;</span>}\mathrm{<span\; class="notranslate">\; \&alpha;</span>}\mathrm{<span\; class="notranslate">\; \&Delta;</span>}\mathrm{<span\; class="notranslate">\; p</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; \&gamma;\&alpha;p</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span>$

In the formula, σ is the confining pressure, in MPa; p _h is the back pressure, in MPa; α is the Biot consolidation coefficient; Δp is the displacement pressure difference, in MPa.

The relationship between displacement pressure p _d and back pressure can be expressed by formula (4):

p _d =p _h +Δp (4)

In the formula, p _d is the displacement pressure in MPa.

According to some specific embodiments of the present invention, wherein, step (5) restores the original irreducible water saturation of the rock core that obtains and comprises: drying the rock core, then weighing the rock core after vacuuming, and weighing the rock core saturated with formation water (using double Cylinder pumps saturate the core with formation water), and then use methane to displace the formation water in the core, and use the weighing method to determine the water saturation of the core.

It can be understood that step (5) is to restore the water saturation of the core to the irreducible water saturation in the original formation, so as to make the stress-sensitivity experiment results more reliable.

According to some specific embodiments of the present invention, wherein in step (5), the rock core is dried at a temperature of 100-110° C. for 48-60 hours, and then weighed after vacuuming the rock core.

According to some specific embodiments of the present invention, wherein in step (5), the rock core is dried, and then the rock core is evacuated to 100-133Pa and then weighed.

According to some specific embodiments of the present invention, wherein step (5) saturates the core with formation water for 24-36 hours, and then uses methane to displace the formation water in the core.

According to some specific embodiments of the present invention, wherein the step (5) saturates the core with formation water, and then uses methane to displace the formation water in the core until the core reaches the original irreducible water saturation.

According to some specific embodiments of the present invention, wherein, step (6) carries out aging treatment to rock core and comprises: applying confining pressure and pore pressure to rock core, and guaranteeing that confining pressure is at least 5.0MPa greater than pore pressure, setting pore pressure, and then Within the variable range of pressure, the confining pressure loading and unloading operations on the core were repeated many times.

According to some specific embodiments of the present invention, the aging treatment of the core in step (6) includes: applying confining pressure and pore pressure to the core, and ensuring that the confining pressure is 5.0-10 MPa greater than the pore pressure.

According to some specific embodiments of the present invention, wherein, step (6) pore pressure is set to 5.0-8Mpa.

According to some specific embodiments of the present invention, wherein step (6) is to increase pore pressure and confining pressure synchronously at intervals of 0.5-1 MPa in steps of 0.5-1 MPa.

According to some specific embodiments of the present invention, wherein, step (6) is to synchronously increase the pore pressure at an interval of 0.5-1 h with a step size of 0.5-1 MPa in the ring pressure pressurization tracking mode and displacement pressure pressurization tracking mode and confining pressure.

During the aging process, the maximum effective stress is smaller than the original effective stress to prevent the decrease in permeability due to the aging process.

The aging process can effectively reduce the influence of the micro-cracks generated during the core sampling process and the gap of the rubber sleeve of the core holder on the experimental results.

According to some specific embodiments of the present invention, wherein, the step (7) recovering the original stress and fluid pressure of the rock core includes further pressurizing the aged core, increasing the pore pressure and the confining pressure synchronously, and maintaining the confining pressure at least greater than the pore pressure 5.0MPa until the pore pressure increases to the original formation pressure, and the confining pressure is raised to the original overburden pressure.

According to some specific embodiments of the present invention, wherein, the step (7) recovering the original stress and fluid pressure of the rock core includes further pressurizing the aged core, increasing the pore pressure and the confining pressure synchronously, and maintaining the confining pressure at least greater than the pore pressure 5.0-10Mpa.

According to some specific embodiments of the present invention, the step (7) is to synchronously increase the pore pressure and the confining pressure at a step size of 0.5-1 MPa and an interval of 0.5-1 h.

According to some specific embodiments of the present invention, step (7) is to synchronously increase the pore pressure and confining pressure at a speed of 0.5-1 MPa with a step size of 0.5-1 h in the annular pressure tracking mode and displacement pressure tracking mode.

It can be understood that when step (7) increases the pore pressure and the confining pressure synchronously, when one of them rises to the original pressure, the other pressure continues to maintain the original speed to rise to the original pressure.

For example, when the pore pressure and confining pressure are increased synchronously in step (7), when the pore pressure increases to the original formation pressure, then keep the pore pressure constant, and continue to increase the confining pressure with a step size of 0.5-1MPa and an interval of 0.5-1h to the original overburden pressure.

According to some specific implementations of the present invention, wherein, step (8) simulates the stress sensitivity of the reservoir during the mining process, including controlling the back pressure to take 3-4MPa as a step size and gradually decreasing at intervals of 0.5-1h (using a high-precision high-pressure pump ), and synchronously adjust the confining pressure and displacement pressure to ensure that the confining pressure is at least 5.0 MPa greater than the pore pressure, and the pressure difference between upstream and downstream is 1.5-2 MPa and remains unchanged. The pore pressure is the algebraic average value of displacement pressure and back pressure, At each test pressure point, after 0.5h of stabilization, record the data of the flowmeter, pressure sensor and differential pressure sensor.

Pore pressure is the algebraic mean of displacement pressure and back pressure.

At each test pressure point, after the flow is stable for 0.5h, record the data of the flowmeter, pressure sensor and differential pressure sensor.

According to some specific embodiments of the present invention, wherein, step (9) data processing and analysis comprises: the data of record is processed and analyzed, obtain the permeability under each test point, draw the relationship curve of permeability-effective stress, thus simulate Analyze the stress sensitivity characteristics when the overburden pressure and pore pressure change simultaneously during the actual exploitation of the reservoir.

According to some specific embodiments of the present invention, a step of initializing the instrument is also included before step (5).

According to some specific embodiments of the present invention, wherein, the step of initializing setting of instrument comprises: first assemble experimental instrument, carry out pressure test work to instrument, check device tightness, then zero-adjust initial value of instrument, set the experimental temperature of constant temperature box, Input the relationship between confining pressure and displacement pressure with back pressure into the depressurization tracking mode of ring pressure tracker and displacement pressure tracker respectively.

On the other hand, the present invention also provides a test device for formation stress sensitivity experiments, wherein the device includes an injection system 1, a core model system 2, a back pressure system 3, a recovery system 4 and a data acquisition system 5; The core model system 2 is respectively connected with the injection system 1 and the back pressure system 3; the back pressure system 3 is connected with the recovery system 4; System 5 is connected to realize data collection.

According to some specific embodiments of the present invention, wherein, the injection system 1 includes a high-pressure gas cylinder 11 (high-purity methane high-pressure gas cylinder), an air compressor 12, a booster pump 13, a displacement pressure tracker 14, and a gas intermediate container 15 , double-cylinder pump 16, and vacuum pump 17; the high-pressure cylinder 11 and the booster pump 13 are connected with the rock core model system 2 through the pipeline sequence, and on the pipeline connected between the booster pump and the rock core model system, the booster pump is used as the starting point to pass through The pipelines are sequentially connected to the outlet port 151 of the gas intermediate container 15, the double-cylinder pump 16 and the vacuum pump 17, and the inlet port 152 of the gas intermediate container 15 is also connected to the displacement pressure tracker 14 through a pipeline; wherein it is preferable that the injection system also It includes at least eight injection system valves 181 , 182 , 183 , 184 , 185 , 186 , 187 , and 188 , and the injection system valves are respectively arranged between each equipment and pipeline crossing points.

The high-purity methane high-pressure gas cylinder is connected to the booster pump through the pipeline, and the booster pump provides a stable high-pressure gas source for the gas intermediate container; the displacement pressure tracker is connected to the gas intermediate container to provide a stable high-pressure gas source for the core model system. And adjust the internal pressure of the model system; the double-cylinder pump provides a stable water source for the core model system, which is used to saturate the formation water; the combination of the evacuation pump and the valve can evacuate the core model system.

According to some specific embodiments of the present invention, wherein, the model system 2 includes a core holder 21, a constant temperature box 22, and a ring pressure tracker 23; the core holder 21 is arranged in the constant temperature box 22, said, One end of the core holder 21 is connected to the booster pump 13 of the injection system 1 through a pipeline, and the other end is connected to the back pressure system 3 through a pipeline; the core holder 21 is connected to the ring pressure tracker 23 through a pipeline connection; preferably the model system 2 also includes at least two model system valves 241, 242, the valves of the model system are respectively arranged on the pipeline connecting the core holder 21 and the ring pressure tracker 23, and the core holder 21 On the pipeline connected with the back pressure system 3.

The holder is equipped with a rock sample, and there is a rubber sleeve between the rock sample and the outer shell of the holder. The ring pressure tracker is connected to the outside of the holder through a valve, and is used to provide rock core Confining pressure. The holder is located in a constant temperature box to simulate the actual temperature environment of the reservoir.

According to some specific embodiments of the present invention, wherein, the back pressure system 3 includes a back pressure valve 31 and a high-pressure pump 32 (high-precision high-pressure pump); Holder 21, recovery system 4 and high-pressure pump 32 are connected; Preferably said back pressure system also comprises at least two back pressure system valves 331,332; Said back pressure system valve is respectively arranged on back pressure valve 31 and high pressure pump 32 and On the pipeline connected to recovery system 4.

The high-pressure pump is connected with the back pressure valve through a valve, and is used to adjust the pressure of the back pressure valve, which can control the output pressure during the simulated mining process.

According to some specific embodiments of the present invention, wherein, the recovery system 4 includes a gas-liquid separator 41, a pool 42 and a gas collection bag 43; the inlet 411 of the gas-liquid separator 41 passes through the pipeline and the backpressure valve of the backpressure system 3 31, the gas outlet 412 of the gas-liquid separator 41 is connected to the gas collection bag 43 through a pipeline, and the liquid outlet 413 of the gas-liquid separator 41 is connected to the pool 42 through a pipeline.

The gas-liquid separator is connected to the outlet valve of the back pressure system, and is used to separate the experimental fluid, and the separated gas and liquid are output to the gas sampling bag and the water pool respectively. The recovery system is mainly used to collect the waste gas and waste liquid generated in the experiment.

According to some specific embodiments of the present invention, wherein, the data acquisition system 5 includes at least three pressure sensors 511, 512, 513, at least one differential pressure sensor 52, at least one gas flow meter 53, and at least one computer 54; wherein Three pressure sensors are respectively arranged on the outlet end 151 of the gas intermediate container 15, the outlet end 241 of the ring pressure tracker 23 and the outlet end 321 of the high pressure pump 32; It is connected with the outlet port 212; the gas flow meter is arranged on the pipeline connecting the gas-liquid separator 41 and the gas collection bag 43; the pressure sensor 51, the differential pressure sensor 52, and the gas flow meter 53 are electrically connected with the computer 54 respectively .

A pressure sensor is connected to the gas intermediate container, the ring pressure tracker, and the outlet of the high-precision high-pressure pump to monitor the displacement pressure, confining pressure and back pressure in real time during the experiment. A differential pressure sensor is connected at the inlet and outlet of the holder to monitor the displacement pressure difference. The inlet port of the ring pressure tracker is connected with the pressure sensor at the back pressure valve, and is used in the simulation process of oil and gas reservoir exploitation to make the confining pressure change synchronously with the change of the back pressure according to formula (3). The inlet end of the displacement pressure tracker is connected with the pressure sensor at the back pressure valve and the pressure difference sensor at the inlet and outlet ends of the rock core, and is used in the simulation process of oil and gas reservoir exploitation, so that the displacement pressure follows the formula (4) with the back pressure changes simultaneously. The gas flow meter at the inlet end of the gas collection bag is used to record the gas flow during the experiment. The computer includes a data acquisition module, a data processing module and a data storage module. The data acquisition module collects the data recorded by the pressure sensor, differential pressure sensor and gas flow meter, and transmits it to the data processing module; the data processing module can obtain the relationship between the core permeability and the effective stress during the experiment through analysis; data storage The module can store the data collected by the data acquisition module and the data obtained by the data processing module.

In the present invention, the "optional" means that it may or may not occur; in other words, an optional technical solution refers to a technical solution that is further modified on the basis of the original technical solution, such as the The preferred technical solution.

To sum up, the present invention provides a test method and device for stratum stress sensitivity experiments. Method of the present invention has following advantage:

Due to the adoption of the above technical scheme, the present invention has the advantage of being able to obtain the quantitative variation relationship between the overlying pressure of the reservoir and the pore pressure during the development of the oil and gas reservoir according to the actual geological data of the oil and gas reservoir. Through the aging treatment in the experiment, the influence of the micro-cracks opened during the core sampling process and the gap of the rubber sleeve of the core holder on the experimental results can be eliminated. The supporting experimental device can realize the function of simulating the mining process, changing the confining pressure and internal pressure synchronously, and can solve the problem of poor stability of displacement pressure difference in the experiment. The experimental method and device can study the stress sensitivity characteristics of the reservoir under the real stress change path during the development of the oil and gas reservoir.

Description of drawings

Fig. 1 is embodiment 1 step flowchart;

FIG. 2 is a schematic diagram of device connection in Embodiment 1.

detailed description

The implementation process and beneficial effects of the present invention are described in detail below through specific examples, aiming to help readers better understand the essence and characteristics of the present invention, and not as a limitation to the scope of implementation of this case.

Example 1

As shown in Figure 2, this example provides a set of stress-sensitivity experimental test devices for simulating the simultaneous change of overburden pressure and pore pressure in tight gas reservoirs, including injection system 1, core model system 2, back pressure system 3, and recovery system 4 And data acquisition system 5. The rock core holder 21 of the rock core model system 2 is connected with the valve 188 of the injection system 1, and the other end of the rock core holder 21 is connected with the back pressure valve 31 of the back pressure system through the valve 242; the other end of the back pressure valve 31 is through the valve 332 It is connected with the gas-liquid separator 41 of the recovery system 4; the data acquisition system communicates with the injection system, the rock core model system, the back pressure system and the recovery system through the pressure sensor 511, the pressure sensor 512, the pressure sensor 513, the gas flow meter 53 and the injection system respectively. connection for data collection.

Injection system 1 consists of high-purity methane high-pressure cylinder 11, air compressor 12, booster pump 13, gas intermediate container 15, displacement pressure tracker 14, double cylinder pump 16, vacuum pump 17, injection system valves (181, 182, 183, 184, 185, 186, 187, 188). The high-purity methane high-pressure gas cylinder 11 is connected to the booster pump 13 through the injection system valve 181, the upper end of the booster pump 13 is connected to the air compressor 12, and the outlet end is connected to the gas intermediate container 15 through the injection system valve 182 and the injection system valve 183. The gas intermediate container 15 provides a stable high-pressure gas source; the outlet port 141 of the displacement pressure tracker 14 is connected to the gas intermediate container 15 through the injection system valve 186 to provide a stable high-pressure gas source for the core model system and adjust the internal pressure of the model system The double-cylinder pump 16 provides a stable water source for the core model system to saturate the formation water; the vacuum pump 17 is combined with the injection system valve 187 to evacuate the core model system.

The core model system 2 includes a core holder 21, a constant temperature box 22, a ring pressure tracker 23, and model system valves (241, 242). A rock sample is housed in the rock core holder 21, and there is a rubber sleeve between the rock sample and the shell of the rock core holder 21 (the shadow of the rock core holder 21 in Fig. 2 ), and the ring pressure tracker 23 passes through the model system valve 241 It is externally connected with the holder 21 and is used to provide confining pressure for the core. The core holder 21 is placed in the constant temperature box 22 to simulate the actual temperature environment of the reservoir. The other end of the core holder 21 is connected with the back pressure system 3 through the core model system valve 242 .

The back pressure system 3 includes a back pressure valve 31, a high-precision high-pressure pump 32, and back pressure system valves (331, 332). The high-precision high-pressure pump 32 is connected to the back pressure valve 31 through the back pressure system valve 331, and is used to adjust the pressure of the back pressure valve 31, and can control the output pressure during the simulated mining process. The other end of the back pressure valve 31 passes through the back pressure system valve 332 Connect with recovery system 4.

The recovery system 4 includes a gas-liquid separator 41 , a water pool 42 , and a gas collection bag 43 . The gas-liquid separator 41 is connected to the valve 332 of the back pressure system, and is used to separate the experimental fluid, and the separated gas and liquid are output to the gas collection bag 43 and the water pool 42 respectively. The recovery system is mainly used to collect the waste gas and waste liquid generated in the experiment.

The data acquisition system includes pressure sensors (511, 512, 513), a differential pressure sensor 52, a gas flow meter 53, and a computer 54. The pressure sensors (511, 512, 513) are respectively connected to the outlet ports (151, 231, 321) of the gas intermediate container 15, the ring pressure tracker 23, and the high-precision high-pressure pump 32, and are used for real-time monitoring of the displacement pressure, ambient pressure and pressure in the experiment. pressure and back pressure. A differential pressure sensor 52 is connected to the inlet and outlet ends (211, 212) of the holder 21 for monitoring the displacement differential pressure. The inlet port 232 of the ring pressure tracker 23 is connected to the pressure sensor 513, and is used in the simulation process of oil and gas reservoir exploitation to make the confining pressure change synchronously with the change of the back pressure according to formula (3). The inlet port 142 of the displacement pressure tracker 14 is connected with the pressure sensor 513 and the differential pressure sensor 52, and is used in the simulation process of oil and gas reservoir production to make the displacement pressure change synchronously with the change of the back pressure according to formula (4). The inlet end of the gas collection bag 43 is connected to a gas flow meter 53 for recording the gas flow during the experiment. The computer 54 includes a data collection module, a data processing module and a data storage module. The data acquisition module collects the data recorded by the pressure sensor (511, 512, 513), the differential pressure sensor 52 and the gas flow meter 53, and transmits it to the data processing module; the data processing module can obtain the rock core permeability in the experimental process through analysis—effective The relationship between stresses, etc.; the data storage module can store the data collected by the data acquisition module and the data obtained by the data processing module.

As shown in Fig. 1, the method for testing the stress sensitivity of tight gas reservoirs with simultaneous changes in overburden pressure and pore pressure by using the above-mentioned device includes the following steps:

(1) Acquire actual geological data of tight gas reservoirs, including: reservoir shape, mechanical property difference between reservoir and surrounding rock, reservoir aspect ratio, depth parameter, shear modulus ratio, reservoir Poisson’s ratio, Non-reservoir Poisson's ratio, reservoir depth, reservoir width, reservoir thickness, reservoir rock density, porosity, Biot consolidation coefficient and other basic parameters.

(2) According to the shape of the reservoir and the difference in mechanical properties between the reservoir and the surrounding rock, select the formula for calculating the pressure arch ratio of the reservoir from Table 1, and obtain the pressure arch ratio. If the shear modulus ratio of the reservoir and the surrounding rock is between 0.8 and 1.2, and the difference in mechanical properties between the reservoir and the surrounding rock is small, the inclusion theory is selected; otherwise, the heterogeneity theory is selected.

(3) Determine the initial formation pressure p ₀ and initial overlying pressure σ ₀ of the reservoir rock. The initial formation pressure _p0 of the reservoir rock is converted from the hydrostatic pressure gradient and calculated according to formula (1). The initial overlying pressure σ ₀ is calculated according to formula (2).

(4) Determine the relationship between confining pressure and displacement pressure with back pressure. The relationship between confining pressure σ and back pressure can be expressed by formula (3), and the relationship between displacement pressure and back pressure can be expressed by formula (4).

(5) Instrument initialization settings. Assemble the experimental instrument according to the experimental device diagram in Fig. 2, and adjust the initial value of the instrument to zero, and set the experimental temperature of the incubator 22. Close the valve 184, and use the booster pump 13 to transfer the gas in the high-purity methane high-pressure cylinder 11 into the gas intermediate container 15. Close the valve 182 and use the displacement pressure tracker 14 to adjust the pressure of the gas intermediate container 15 . After being stabilized, slowly open the valve 184, so that the high-pressure gas is slowly transferred into the experimental system, and the pressure test is carried out to check the tightness of the device. Input the relationship between confining pressure and displacement pressure with back pressure into the depressurization tracking mode of ring pressure tracker and displacement pressure tracker respectively.

(6) Restoration of core irreducible water saturation. First, close valve 184, valve 185, and valve 242, and dry the core at a constant temperature for 48 hours. Next, open the valve 187 and the valve 188, utilize the vacuum pump 17 to evacuate the rock core and weigh it. Then, close the valve 187, open the valve 185, the valve 188, and the valve 242, and use the double-cylinder pump 16 to saturate the formation water for 24 hours. Finally, close the valve 185, open the valve 184, use high-purity methane to displace the formation water in the core, and use the weighing method to establish the irreducible water saturation.

(7) Core aging treatment. The confining pressure and pore pressure are applied to the core, the confining pressure is controlled by the ring pressure tracker 23 , the back pressure is controlled by the high-precision high-pressure pump 32 , and the inlet pressure is controlled by the displacement pressure tracker 14 . In the ring pressure tracking mode and displacement pressure tracking mode, the pore pressure and confining pressure are slowly and synchronously increased with a step size of 1 MPa and an interval of 0.5 h to ensure that the confining pressure is at least 5.0 MPa greater than the pore pressure. When the pore pressure increases to 5.0MPa, keep the pore pressure constant, increase the confining pressure to 15MPa with 1MPa as the step size and 0.5h as the interval, and cycle the pressure relief and pressurization between 15-10MPa for aging treatment. . During the aging process, the maximum effective stress is smaller than the original effective stress to prevent the decrease in permeability caused by the aging process. The aging process can effectively reduce the influence of the micro-cracks generated during the core sampling process and the gap of the rubber sleeve of the core holder on the experimental results.

(8) Restoration of original core stress and fluid pressure. After the aging treatment is completed, the core is further pressurized to ensure that the confining pressure is at least 5.0 MPa greater than the pore pressure. In the ring pressure tracking mode and displacement pressure tracking mode, the pore pressure is slowly and synchronously increased with a step size of 1 MPa and an interval of 0.5 h and confining pressure until the pore pressure increases to the original formation pressure, then keep the pore pressure constant, and increase the confining pressure to the original overburden pressure with a step size of 1MPa and an interval of 0.5h.

(9) Simulate the stress sensitivity of the reservoir during mining. The back pressure is controlled by the high-precision high-pressure pump 32 with a step size of 3-4MPa and gradually decreased at intervals of 0.5-1h. In the ring pressure tracking mode and displacement pressure tracking mode, according to formula (3) and formula (4) Synchronously adjust the confining pressure and displacement pressure to ensure that the confining pressure is at least 5.0MPa greater than the pore pressure, and the pressure difference between upstream and downstream is 1.5-2MPa and remains unchanged. High-speed non-Darcy seepage is likely to occur when the displacement pressure difference is greater than 2 MPa, and slippage seepage is likely to occur when the displacement pressure difference is less than 1.5 MPa. Pore pressure is the algebraic mean of displacement pressure and back pressure. At each test pressure point, the data of the flow meter 53, the pressure sensor 511, the pressure sensor 512, the pressure sensor 513, and the differential pressure sensor 52 were recorded after the flow was stabilized for 0.5 hours.

(10) Data processing and analysis. By processing and analyzing the data recorded by the computer 54, the permeability at each test point can be obtained, and the relationship curve between permeability and effective stress can be drawn, so as to simulate and analyze the overburden pressure and pore pressure in the actual mining process of the reservoir. Stress-sensitive features when changed.

Claims (10)

1. a formation stress sensitive experimental testing method, wherein, said method comprises the steps: (1) Obtain actual geological data; preferably, the geological data include at least the shape of the reservoir and the difference in mechanical properties between the reservoir and the surrounding rock; optionally, the aspect ratio, depth parameter, and shear modulus ratio of the reservoir are also included A combination of one or more of , reservoir Poisson's ratio, non-reservoir Poisson's ratio, reservoir depth, reservoir width, reservoir thickness, reservoir rock density, porosity, and Biot's consolidation coefficient. (2) According to the shape of the reservoir and the difference in mechanical properties between the reservoir and the surrounding rock, select the formula for calculating the pressure-arch ratio of the reservoir; when the shear modulus ratio between the reservoir and the surrounding rock is between 0.8-1.2, select inclusions theory, otherwise choose heterogeneity theory; (3) Determine the initial formation pressure and initial overlying pressure of the reservoir rock; (4) Determine the relationship between confining pressure and displacement pressure with back pressure; (5) recover the undeveloped rock core with natural fractures to the original irreducible water saturation; (6) carry out aging treatment to rock core; (7) Restoring the original stress and fluid pressure of the rock core; (8) Simulate the stress sensitivity of the reservoir during the mining process; (9) Data processing and analysis. 2. The method according to claim 1, wherein, step (5) restores the original irreducible water saturation of the obtained rock core and comprises: drying the rock core (preferably drying at a temperature of 100-110°C for 48-60h ), then the core is evacuated (preferably vacuumed to 100-133Pa) and weighed, the core is saturated with formation water (preferably saturated with formation water for 24-36h), and then the formation water in the core is displaced with methane (preferably displaced until The core reaches the original irreducible water saturation), and the water saturation of the core is determined by weighing method. 3. method according to claim 1, wherein, step (6) carries out aging treatment to rock core and comprises: rock core is applied confining pressure and pore pressure, and guarantees that confining pressure is larger than pore pressure 5.0-10MPa, sets pore pressure ( Preferably, the pore pressure is set to 5.0-8.0MPa), and then within the variable range of confining pressure, the confining pressure loading and unloading operations on the core are repeated several times; preferably, the step length is 0.5-1MPa, and the interval is 0.5-1h Simultaneously increase pore pressure and confining pressure. 4. The method according to claim 1, wherein, step (7) restores the core original stress and fluid pressure and includes further increasing the pressure on the aged core, synchronously increasing pore pressure and confining pressure, and maintaining confining pressure ratio pore Increase the pressure by 5.0-10MPa until the pore pressure increases to the original formation pressure, and the confining pressure rises to the original overlying strata pressure; it is preferable to increase the pore pressure and confining pressure synchronously at intervals of 0.5-1MPa in steps of 0.5-1MPa. 5. The method according to claim 1, wherein, simulating the stress sensitivity of the reservoir during the exploitation process includes controlling the back pressure to gradually reduce (preferably controlling the back pressure to take 3-4MPa as a step size and gradually taking 0.5-1h as an interval decrease), and synchronously adjust the confining pressure and displacement pressure to ensure that the confining pressure is at least 5.0 MPa greater than the pore pressure, and the pressure difference between upstream and downstream is 1.5-2 MPa, and remains unchanged. The pore pressure is the algebraic average value of displacement pressure and back pressure , at each test pressure point, record the data of the flowmeter, pressure sensor and differential pressure sensor after being stabilized for 0.5h. 6. The method according to claim 1, wherein, step (2) according to the shape of the reservoir and the mechanical property difference of the reservoir and the surrounding rock, selects the formula for calculating the arch ratio of the reservoir pressure as follows: 7. A formation stress sensitive experimental testing device, wherein said device comprises an injection system (1), a rock core model system (2), a back pressure system (3), a recovery system (4) and a data acquisition system (5); Described rock core model system (2) is respectively connected injection system (1) and back pressure system (3); Back pressure system (3) is connected with recovery system (4) again; Described injection system (1), rock core model The system (2), the back pressure system (3), and the recovery system (4) are respectively connected with the data acquisition system (5) to realize data acquisition. 8. The device according to claim 7, wherein the injection system (1) comprises a high-pressure cylinder (11), an air compressor (12), a booster pump (13), a displacement pressure tracker (14) , gas intermediate container (15), double cylinder pump (16) and vacuum pump (17); On the pipeline connected to the pump and the core model system, the booster pump is used as the starting point to connect with the outlet port (151) of the gas intermediate container (15), the double-cylinder pump (16) and the vacuum pump (17) through the pipeline sequence, and the gas intermediate container The inlet port (152) of (15) is also connected with the displacement pressure tracker (14) through a pipeline; wherein preferably the injection system also includes at least eight injection system valves (181, 182, 183, 184, 185, 186 , 187, 188), the valves of the injection system are respectively arranged between each equipment and the intersection of pipelines; it is also preferred that the model system (2) includes a core holder (21), a thermostat (22), and Ring pressure tracker (23); said rock core holder (21) is arranged in the constant temperature box (22), and one end of said rock core holder (21) passes through the booster pump ( 13) connection, the other end is connected with the back pressure system (3) through the pipeline; the core holder (21) is connected with the ring pressure tracker (23) through the pipeline; wherein preferably the model system (2) also Including at least two model system valves (241, 242), the model system valves are respectively arranged on the pipeline connecting the core holder (21) and the ring pressure tracker (23), and the core holder (21) and On the pipeline connected to the back pressure system (3). 9. The device according to claim 7, wherein the back pressure system (3) comprises a back pressure valve (31) and a high pressure pump (32); the back pressure valve (31) passes through the pipeline and the model respectively The core holder (21) of the system (2), the recovery system (4) and the high-pressure pump (32) are connected; preferably the back pressure system also includes at least two back pressure system valves (331, 332); Pressure system valve is arranged on the pipeline that back pressure valve (31) is connected with high-pressure pump (32) and recovery system (4) respectively; Also preferably described recovery system (4) comprises gas-liquid separator (41), pool (42 ) and a gas sampling bag (43); the inlet (411) of the gas-liquid separator (41) is connected with the back pressure valve (31) of the back pressure system (3) through a pipeline, and the gas outlet of the gas-liquid separator (41) (412) is connected with gas collection bag (43) through pipeline, and the liquid outlet (413) of gas-liquid separator (41) is connected with pool (42) through pipeline. 10. The device according to claim 7, wherein the data acquisition system (5) comprises at least three pressure sensors (511, 512, 513), at least one differential pressure sensor (52), at least one gas flow meter ( 53), and at least one computer (54); wherein three pressure transducers are respectively arranged on the outlet port (151) of the gas intermediate container (15), the outlet port (241) of the ring pressure tracker (23) and the high pressure pump ( 32) at the outlet end (321); the differential pressure sensor (52) is connected with the inlet end (211) and the outlet end (212) of the core holder (21); the gas flowmeter is arranged on the gas-liquid separator (41) on the pipeline that is connected with gas collection bag (43); described pressure sensor (51), differential pressure sensor (52), and gas flowmeter (53) are electrically connected with computer (54) respectively.