CN111550236B - A simulation experiment method for fracture closure coefficient of shale oil and gas reservoirs - Google Patents

Abstract

The embodiment of the invention provides a simulation experiment method for a shale oil-gas reservoir fracture closure coefficient, which comprises the following steps: placing the two guide plates into a guide chamber, weighing a proppant with preset mass, uniformly and flatly paving the proppant between the two guide plates, and obtaining a corresponding relation between the closing pressure of the proppant and the pore volume change of the proppant through a crack conductivity test experiment; adopting linear function fitting to obtain a fitting straight line for the corresponding relation between the closing pressure and the pore volume variation of the proppant, and determining the slope of the fitting straight line as the pore compression coefficient of the proppant; and obtaining the fracture closure coefficient of the proppant according to the pore compression coefficient, the initial distance between the two guide plates, the length of the guide chamber and the height of the guide chamber. The closure coefficient of the embodiment of the invention can be directly applied to numerical simulation of shale oil and gas reservoirs.

Description

A simulation experiment method for fracture closure coefficient of shale oil and gas reservoirs

technical field

The embodiments of the present invention relate to the technical field of oil and gas reservoir exploration and development, and in particular, to a simulation experiment method for fracture closure coefficient of shale oil and gas reservoirs.

Background technique

Shale oil and gas reservoirs have the characteristics of low porosity and low permeability. If fracturing is not implemented to form a fracture network zone and provide sufficient flow channels for shale oil and gas, industrial production and recovery will not be obtained. The current shale oil and gas production technologies mainly include horizontal well multi-stage and multi-cluster fracturing technology, slick water ultra-large volume fracturing and simultaneous fracturing technology. These effective stimulation technologies can greatly improve the production of shale oil and gas wells.

Rock oil and gas reservoirs are different from traditional low-permeability oil and gas reservoirs. In traditional tight reservoirs, a single main fracture is formed through hydraulic fracturing. The main purpose is to increase the length of the main fracture and the fracture conductivity, and to increase the contact area between the fracture and the reservoir. , to increase the production of oil and gas wells. The matrix fractures in shale oil and gas reservoirs are extremely low, reaching the Nadaxi level and basically impermeable. Therefore, only forming a single main fracture has limited stimulation effect. However, shale oil and gas reservoirs generally have well-developed bedding and natural fractures, and the core is brittle. Through large-scale hydraulic fracturing, a network of fractures can be formed, which can connect the bedding and natural fractures, and effectively increase the fracture and the reservoir. The contact area allows the oil flow to pass through the matrix to the fracture and then to the bottom of the well, thereby effectively improving the production of oil and gas reservoirs. By fracturing the shale oil and gas reservoir into the fracture network, the reservoir is called the shale oil and gas reservoir reformation volume, and the shale oil and gas in the reformed volume can be effectively exploited in the shale gas reservoir bedding and microfracture development degree, brittleness The degree of fracturing, the scale of fracturing and the fracturing process jointly determine the size of the fracturing stimulation volume and the complexity of the fractures. The larger the stimulation volume and the more complex the fractures, the better the fracturing stimulation effect. After the fracture is formed under the action of high-pressure fluid, the well is shut in for a period of time to wait for the formation pressure to redistribute, and then the well is opened and released. In the blowout stage, as the fluid flows back from the fracture to the bottom of the well, the pressure in the fracture will gradually decrease, and the width, length and height of the fracture will also decrease with the decrease in pressure, but under the support of proppant Cracks with a certain width, length and height are formed.

In the process of numerical simulation of fractures in shale oil and gas reservoirs, the design of hydraulic fractures requires the input of fracture length, fracture width and fracture height. The conventional fracture compressibility is limited to the change of fracture volume with pressure, so the volume compressibility cannot be directly applied to shale. In the numerical simulation of fractures in oil and gas reservoirs, it is urgent to design an experimental method to determine the degree of fracture closure to guide the numerical simulation of fractures in shale oil and gas reservoirs.

SUMMARY OF THE INVENTION

The embodiment of the present invention provides a simulation experiment method for the fracture closure coefficient of shale oil and gas reservoirs, and the closure coefficient can be directly applied to the numerical simulation of fractures of shale oil and gas reservoirs.

The embodiment of the present invention provides a simulation experiment method for the fracture closure coefficient of shale oil and gas reservoirs, including:

Place the two guide plates in the guide chamber, weigh the proppant of preset quality, spread the proppant evenly between the two guide plates, and obtain the closure of the proppant through the fracture conductivity test experiment. Corresponding relationship between pressure and proppant pore volume change;

For the corresponding relationship between the closing pressure and the change of the pore volume of the proppant, a fitting straight line is obtained by fitting a linear function, and the slope of the fitting straight line is determined as the pore compression coefficient of the proppant;

According to the pore compressibility coefficient, the initial distance between the two guide plates, and the length of the guide chamber and the height of the guide chamber, the fracture closure coefficient of the proppant is obtained.

In a specific embodiment of the present invention,

The corresponding relationship between the closing pressure of the proppant and the change in the pore volume of the proppant is obtained through the fracture conductivity test experiment, including:

Connect the diversion chamber to the pipeline of the fracture conductivity testing device, place a sealed measuring cylinder at the liquid outlet, and place the measuring cylinder on the balance;

Turn on the gas tank switch of the fracture conductivity test device, so that the liquid passes through the pipeline through the flow diversion chamber and finally reaches the measuring cylinder;

When the liquid flows into the graduated cylinder stably, close the gas tank and clear the balance;

Set the closing pressure increase value, record the closing pressure and the mass of water in the balance cylinder every second, and set the fracture conductivity test device to close when the closing pressure reaches the preset limit. The mass of water is the volume of water, and the volume of water is Characterize the change in the pore volume of the proppant;

The corresponding relationship between the closing pressure and the change in the pore volume of the proppant was recorded.

In a specific embodiment of the present invention, the fracture closure coefficient of the proppant is obtained according to the pore compressibility coefficient, the initial distance between the two guide plates, and the length of the guide chamber and the height of the guide chamber, The formula is:

in,

In the formula, C _f —— is the closure coefficient of the crack, Mpa ^-1 ;

B _f —pore compressibility;

ΔV _w — is the change in pore volume of the proppant, cm ³ , Δp — is the change in the closing pressure, MPa;

a—characterizes the length of the simulated crack, the length of the diversion chamber, cm;

b—characterizes the height of the simulated fracture, which is the width of the diversion chamber, cm;

c—characterizes the width of the initial simulated crack, which is the initial distance between the two guide plates of the guide chamber, cm.

In a specific embodiment of the present invention, the length of the guiding chamber is 17.7 cm, and the width of the guiding chamber is 3.8 cm.

In a specific embodiment of the present invention, the preset limit value is 70Mpa.

In a specific embodiment of the present invention, the closed pressure boost value is 5 MPa.

In a specific embodiment of the present invention, the support is one of the following:

Quartz sand, metal aluminum balls, walnut shells, glass beads, plastic balls, steel balls, ceramsite and resin-coated sand.

In the simulation experiment method for the fracture closure coefficient of shale oil and gas reservoirs provided by the embodiment of the present invention, two guide plates are placed in a guide chamber, a proppant of preset quality is weighed, and the proppant is evenly spread on the two guide plates. Between the guide plates, the corresponding relationship between the closing pressure of the proppant and the change of the pore volume of the proppant is obtained through the fracture conductivity test experiment; the corresponding relationship between the closing pressure and the change of the pore volume of the proppant is fitted by a linear function The fitting straight line is obtained, and the slope of the fitting straight line is determined as the pore compressibility coefficient of the proppant; according to the pore compressibility coefficient, the initial distance between the two guide plates, the length of the guide chamber and the height of the guide chamber, we get The fracture closure coefficient of the proppant. Using the distance between the two guide plates, the length of the guide chamber and the height of the guide chamber, the initial simulated fracture width, simulated fracture length and simulated fracture height are respectively characterized, and the obtained closure coefficient can be used for shale oil and gas reservoirs. in the numerical simulation.

Description of drawings

In order to illustrate the embodiments of the present invention or the technical solutions in the prior art more clearly, the following briefly introduces the accompanying drawings that are used in the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description The drawings are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can also be obtained based on these drawings without any creative effort.

FIG. 1 is a schematic flowchart of a simulation experiment method of a fracture closure coefficient of a shale oil and gas reservoir provided by an embodiment of the present invention;

2 is a schematic diagram of the proppant provided in the embodiment of the present invention before the experiment in the diversion chamber;

3 is a schematic diagram of the proppant provided in the embodiment of the present invention after the experiment in the diversion chamber;

FIG. 4 is a corresponding relationship diagram between the closing pressure and the change of the pore volume of the proppant provided by the embodiment of the present invention;

FIG. 5 is a fitting curve diagram of the corresponding relationship between the closing pressure and the change of the pore volume of the proppant provided by the embodiment of the present invention.

Detailed ways

In order to make the purposes, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments These are some embodiments of the present invention, but not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

It should be noted that when an element is referred to as being "fixed to" or "disposed on" another element, it can be directly on the other element or indirectly on the other element. When an element is referred to as being "connected to" another element, it can be directly connected to the other element or indirectly connected to the other element.

It is to be understood that the terms "length", "width", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top" , "bottom", "inside", "outside", etc. indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, which are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying the indicated device. Or elements must have a particular orientation, be constructed and operate in a particular orientation, and therefore should not be construed as limiting the invention.

In addition, the terms "first" and "second" are only used for descriptive purposes, and should not be construed as indicating or implying relative importance or implying the number of indicated technical features. Thus, a feature defined as "first" or "second" may expressly or implicitly include one or more of that feature. In the description of the present invention, "plurality" and "several" mean two or more, unless otherwise expressly and specifically defined.

At present, the existing shale oil and gas reservoirs have the characteristics of low porosity and low permeability. If fracturing is not implemented to form a fracture network zone and provide sufficient flow channels for shale oil and gas, industrial production and recovery will not be obtained. The current shale oil and gas production technologies mainly include horizontal well multi-stage and multi-cluster fracturing technology, slick water ultra-large volume fracturing and simultaneous fracturing technology. These effective stimulation technologies can greatly improve the production of shale oil and gas wells. Rock oil and gas reservoirs are different from traditional low-permeability oil and gas reservoirs. In traditional tight reservoirs, a single main fracture is formed through hydraulic fracturing. The main purpose is to increase the length of the main fracture and the fracture conductivity, and to increase the contact area between the fracture and the reservoir. , to increase the production of oil and gas wells. The matrix fractures in shale oil and gas reservoirs are extremely low, reaching the Nadaxi level and basically impermeable. Therefore, only forming a single main fracture has limited stimulation effect. However, shale oil and gas reservoirs generally have well-developed bedding and natural fractures, and the core is brittle. Through large-scale hydraulic fracturing, a network of fractures can be formed, which can connect the bedding and natural fractures, and effectively increase the fracture and the reservoir. The contact area allows the oil flow to pass through the matrix to the fracture and then to the bottom of the well, thereby effectively improving the production of oil and gas reservoirs. By fracturing the shale oil and gas reservoir into the fracture network, the reservoir is called the shale oil and gas reservoir reformation volume, and the shale oil and gas in the reformed volume can be effectively exploited in the shale gas reservoir bedding and microfracture development degree, brittleness The degree of fracturing, the scale of fracturing and the fracturing process jointly determine the size of the fracturing stimulation volume and the complexity of the fractures. The larger the stimulation volume and the more complex the fractures, the better the fracturing stimulation effect. After the fracture is formed under the action of high-pressure fluid, the well is shut in for a period of time to wait for the formation pressure to redistribute, and then the well is opened and released. In the blowout stage, as the fluid flows back from the fracture to the bottom of the well, the pressure in the fracture will gradually decrease, and the width, length and height of the fracture will also decrease with the decrease in pressure, but under the support of proppant Cracks with a certain width, length and height are formed. In the numerical simulation software, the design of hydraulic fractures needs to input the fracture length, fracture width and fracture height. The conventional fracture compressibility is limited to the change of fracture volume with pressure, which cannot be directly applied to numerical simulation. Therefore, it is urgent to design an experimental method. to determine the extent of fracture closure to guide numerical simulations.

In order to express the relationship between the shrinkage value of the fracture body and the pressure drop value of the formation, the concept of fracture closure coefficient is introduced. In order to be suitable for numerical simulation calculation, it is convenient to evaluate the degree of fracture closure after pressure reduction. The so-called fracture closure coefficient refers to the reduction value of the fracture width per unit fracture width when the pressure decreases by unit pressure, namely:

The formula of the fracture closure coefficient is:

In the formula, C _f —— the closure coefficient of the fracture, Mpa ^-1

W _f ——the width of the initial crack, m

Δp——fracture pressure change, Mpa

_Δpe ——the effective pressure change in the seam, Mpa

ΔW _p ——the shrinkage value of the crack width when the crack pressure decreases, m.

The embodiment of the present invention provides a simulation experiment method for the fracture closure coefficient of shale oil and gas reservoirs. Through the diversion experiment, the distance between two diversion plates, the length of the diversion chamber and the height of the diversion chamber are used to determine the The initial simulated fracture width, simulated fracture length, and simulated fracture height are characterized, so that the obtained closure coefficient can be used in the numerical simulation of shale oil and gas reservoirs.

Referring to FIG. 1, FIG. 1 is a schematic flowchart of a simulation experiment method for a fracture closure coefficient of a shale oil and gas reservoir provided by an embodiment of the present invention, and the detailed steps are as follows:

Step 101: Place the two guide plates in the guide chamber, weigh the proppant of preset quality, spread the proppant evenly between the two guide plates, and obtain the proppant through the fracture conductivity test experiment The corresponding relationship between the closing pressure of the proppant and the change in the pore volume of the proppant.

Specifically, this step includes:

Connect the diversion chamber to the pipeline of the fracture conductivity testing device, place a sealed measuring cylinder at the liquid outlet, and place the measuring cylinder on the balance;

Turn on the gas tank switch of the fracture conductivity test device, so that the liquid passes through the pipeline through the flow diversion chamber and finally reaches the measuring cylinder;

When the liquid flows into the graduated cylinder stably, close the gas tank and clear the balance;

Set the closing pressure increase value, record the closing pressure and the mass of water in the balance cylinder every second, and set the fracture conductivity test device to close when the closing pressure reaches the preset limit. The mass of water is the volume of water, and the volume of water is Characterize the change in the pore volume of the proppant;

The corresponding relationship between the closing pressure and the change in the pore volume of the proppant was recorded.

In this embodiment, the fracture conductivity testing device includes: 1. A linear flow guiding chamber (radial flow guiding chamber) conforming to API standards; the test area is 67.3 cm ² , and rock can be added to the upper and lower ends of the proppant Die with removal tool. 2. Core holder, circulation holder 3. Hydraulic press and pressure compensation system; 4. Linear displacement sensor; 5. Test liquid displacement system, including displacement pump and liquid storage container; 6. Differential pressure gauge, pressure Sensor; 7. Back pressure regulating system; 8. Balance; 9. Heating and temperature control system; 10. Vacuum system; 11. Automatic control system; 12. Data acquisition and processing system. Through the high-pressure nitrogen in the nitrogen bottle, the liquid in the storage tank is pressed into the guide chamber, and the liquid flows through the intermediate pipeline, the guide chamber, and reaches the measuring cylinder on the balance.

In this embodiment, the length of the guiding chamber is 17.7 cm, and the width of the guiding chamber is 3.8 cm. The guide plate of the guide chamber is an iron plate.

In a specific embodiment of the present invention, the preset limit value is 70Mpa.

In a specific embodiment of the present invention, the closed pressure boost value is 5 MPa.

Specifically, the iron plate is placed in the diversion chamber for testing the conductivity of the fracture, and the proppant of the same quality is taken, and the proppant is spread evenly between the iron plates. as shown in picture 2.

Place the diversion chamber in the fracture conductivity test device, connect the diversion chamber to the pipeline, place it in a well-sealed measuring cylinder at the liquid outlet, and place the measuring cylinder on the balance. Turn on the gas tank switch, so that the liquid flows through the pipeline to the guide chamber and finally reaches the graduated cylinder. When the liquid flows into the graduated cylinder stably, close the gas tank and clear the balance.

Set the closing pressure increase value (the closing pressure boost value can be 5MPA), record the closing pressure and the quality of the balance every second, and set the closing pressure to 70Mpa to close the instrument. After the experiment, the proppant distribution in the diversion chamber is shown in Figure 3.

Step 102 : For the corresponding relationship between the closing pressure and the change in the pore volume of the proppant, a linear function is used to obtain a fitted straight line, and the slope of the fitted straight line is determined as the pore compression coefficient of the proppant.

In this embodiment, the slope of the fitted line is the ratio of the change in the pore volume of the proppant to the closing pressure.

It can be expressed by the following formula:

In the formula, ΔV _w — is the change in the pore volume of the proppant, cm ³ , and Δp — is the closing pressure, MPa.

Specifically, the data of the corresponding relationship between the closing pressure and the change in the pore volume of the proppant are derived, and a curve between the closing pressure and the volume is obtained by conversion, as shown in Figure 4, and the slope of the straight line obtained by fitting a linear function is shown in Figure 5. The slope is the pore compressibility of the proppant.

Step 103: Obtain the fracture closure coefficient of the proppant according to the pore compressibility coefficient, the initial distance between the two guide plates, and the length of the guide chamber and the height of the guide chamber.

Specifically, according to the pore compression coefficient, the initial distance between the two guide plates, and the length of the guide chamber and the height of the guide chamber, the fracture closure coefficient of the proppant is obtained, and the formula is:

in,

In the formula, C _f —— is the closure coefficient of the crack, Mpa ^-1 ;

B _f —pore compressibility;

ΔV _w —— is the change of the pore volume of the proppant in cm ³ , Δp —— is the closing pressure MPa;

a—characterizes the length of the simulated crack, the length of the diversion chamber, cm;

b—characterizes the height of the simulated fracture, which is the width of the diversion chamber, cm;

c—characterizes the width of the initial simulated crack, which is the initial distance between the two guide plates of the guide chamber, cm.

Substituting formula (3) into formula (2), the following formula can be obtained:

相当于公式(1)中的ΔW_p。In formula (4), c is equivalent to W _f in formula (1), ΔP is the closing pressure change, which is equivalent to the fracture pressure change in formula (1),

Equivalent to ΔW _p in formula (1).

It should be noted that the proppant in the embodiment of the present invention can be one of the following:

Quartz sand, metal aluminum balls, walnut shells, glass beads, plastic balls, steel balls, ceramsite and resin-coated sand.

It can be seen from the above description that two guide plates are placed in the guide chamber, the proppant of preset quality is weighed, and the proppant is evenly spread between the two guide plates. Through the fracture conductivity test experiment, Obtain the corresponding relationship between the closing pressure of the proppant and the change in the pore volume of the proppant; for the corresponding relationship between the closing pressure and the change in the pore volume of the proppant, a linear function is used to obtain a fitted straight line, and the slope of the fitted straight line is determined as the proppant The pore compressibility coefficient of the proppant; the fracture closure coefficient of the proppant is obtained according to the pore compressibility coefficient, the initial distance between the two guide plates, and the length and height of the guide chamber. The closure coefficient in the embodiment of the present invention can be directly applied to the numerical simulation of shale oil and gas reservoirs.

The embodiments or implementations in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments, and the same and similar parts between the various embodiments may be referred to each other.

In the description of this specification, reference to the terms "one embodiment," "some embodiments," "exemplary embodiment," "example," "specific example," or "some examples", etc., is meant to incorporate the embodiments A particular feature, structure, material, or characteristic described or exemplified is included in at least one embodiment or example of the present invention. In this specification, schematic representations of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the particular features, structures, materials or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, but not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: The technical solutions described in the foregoing embodiments can still be modified, or some or all of the technical features thereof can be equivalently replaced; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the technical solutions of the embodiments of the present invention. scope.

Claims (7)

1. A simulation experiment method for shale oil and gas reservoir fracture closure coefficient is characterized by comprising the following steps:

placing the two guide plates into a guide chamber, weighing a proppant with preset mass, uniformly and flatly paving the proppant between the two guide plates, and obtaining a corresponding relation between the closing pressure of the proppant and the pore volume change of the proppant through a crack conductivity test experiment;

adopting linear function fitting to obtain a fitting straight line for the corresponding relation between the closing pressure and the pore volume variation of the proppant, and determining the slope of the fitting straight line as the pore compression coefficient of the proppant;

and obtaining the fracture closure coefficient of the proppant according to the pore compression coefficient, the initial distance between the two guide plates, the length of the guide chamber and the height of the guide chamber.

2. The method of claim 1, wherein the obtaining the corresponding relationship between the closing pressure of the proppant and the pore volume change of the proppant through a fracture conductivity test experiment comprises:

connecting the flow guide chamber into a pipeline of the crack flow guide capacity testing device, placing a sealed measuring cylinder at the liquid outlet, and placing the measuring cylinder on a balance;

opening a gas tank switch of the crack flow conductivity testing device, so that the liquid finally reaches the measuring cylinder through the pipeline in the flow conductivity chamber;

closing the gas tank when the liquid stably flows into the measuring cylinder, and resetting the balance;

setting a closing pressure increase value, recording closing pressure and the mass of water in a balance measuring cylinder per second, and closing the crack flow conductivity testing device when the closing pressure reaches a preset limit value, wherein the mass of the water is the volume of the water, and the volume of the water represents the pore volume variation of the proppant;

and recording the corresponding relation between the obtained closing pressure and the pore volume change of the proppant.

3. The method of claim 1, wherein the fracture closure coefficient of the proppant is obtained from the pore compressibility, the initial distance between two baffles, and the length and height of the baffle compartment by the formula:

wherein,

in the formula, C_fThe closure factor of the crack, Mpa^-1；

B_f-a pore compressibility;

ΔV_w-as proppant pore volume change, cm³Δ p — is the closing pressure variation, MPa;

a, representing the length of the simulated crack, which is the length of the diversion chamber, cm;

b, representing the height of the simulated crack, wherein the height is the width of the diversion chamber in cm;

c, representing the initial simulated crack width, which is the initial distance, cm, between the two guide plates of the guide chamber.

4. A method according to any of claims 1-3, characterized in that the length of the diversion chamber is 17.7cm and the width of the diversion chamber is 3.8 cm.

5. Method according to claim 2, characterized in that said preset limit is 70 MPa.

6. A method according to any of claims 2-3, characterized in that the closing pressure boost value is 5 MPa.

7. The method of any one of claims 1-3, wherein the proppant is one of:

quartz sand, metal aluminum balls, walnut shells, glass beads, plastic balls, steel balls, ceramsite and resin coated sand.

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