CN102720486B - Device for testing shale gas fracture network diversion capacity and working method of device - Google Patents

Abstract

The invention relates to a device for testing the diversion capacity of a shale gas fracture network, which includes a rectangular diversion chamber, a gas flow meter, a differential pressure gauge and a displacement meter; the diversion chamber includes a side wall, and a The upper piston and the lower piston, the diversion cavity enclosed by the side wall, the upper piston and the lower piston, the upper cover plate is installed on the upper piston, the lower cover plate is installed under the lower piston, in the diversion cavity, and Marbles simulating shale cracks are arranged between the upper piston and the lower piston. The present invention fills the gap that the conductance capacity of shale gas fracture network cannot be measured by experimental means, and can measure the conduction capacity under different fracture network models; the diversion chamber described in the present invention is different from the traditional API standard diversion chamber : The end of the traditional API standard diversion chamber is arc-shaped, while the end of the diversion chamber of the present invention is square, and its volume is 6 times that of the traditional API standard diversion chamber, which can conduct research on the diversion capacity of complex fracture networks.

Description

A device for testing the conductivity of shale gas fracture network and its working method

technical field

The invention relates to a device for testing the conductivity of a shale gas fracture network and a working method thereof, belonging to the technical field of oil and gas field development.

Background technique

my country's traditional oil and gas fields have entered the mid-to-late stage of development, and their production capacity has declined significantly. Therefore, it is imperative to find new alternative energy sources. Shale gas is one of the important replacement resources for conventional oil and gas resources. As an emerging unconventional energy source, shale gas has huge reserves and plays an important role in alleviating the pressure on energy supply, developing a low-carbon economy, and adjusting and optimizing the energy structure. Compared with conventional natural gas, shale gas development has the advantages of long mining life, long production cycle, and stable production capacity. In recent years, the state has paid special attention to the development of shale gas, and has given important support in terms of policies and funds. Therefore, it is of great significance to strengthen the research on shale gas exploitation technology to maintain economic development and alleviate energy pressure.

Shale reservoirs have low natural pressure and low permeability (less than 0.001×10 ^-3 μm2), usually have no natural production capacity, and often require fracturing measures to be effectively exploited. Shale gas fracturing usually uses slick water or clear water to carry proppant into the formation in a high-displacement, low-viscosity method to achieve the function of communicating natural fractures and forming a complex fracture network (fracture network) in the formation. The fundamental starting point of shale gas fracturing design is how to form an effective network of fractures. Whether shale gas can be produced effectively depends largely on the size of the interlaced network fractures formed by fracturing fractures and the opening of induced natural fractures during the fracturing process. The conductivity of the fracture network directly affects the performance of shale gas wells. production index. Therefore, it is of great significance to study the conductivity of the fracture network in shale gas reservoirs to improve the stimulation effect of fracturing.

The traditional hydraulic fracturing method uses high-viscosity fracturing fluid to carry the proppant into the formation, forming a sand-filled fracture with high conductivity in the formation. For the conductivity of a fracture filled with proppant, fracture conductivity can be used The technique of evaluating the conductivity of the acid-etched fractures formed by acidification measures is relatively mature, and the research method for the conductivity of the acid-etched fractures formed by the acidification measures is also relatively mature, and a systematic theory and rating system have been formed. The above two traditional fracture conductivity evaluation methods evaluate a single fracture in the formation, and the fracture network is a fracture system formed in the formation that communicates with each other, has a complex shape, varies in width, and criss-cross, so the traditional The evaluation method is directly applied to the fracture network formed by shale gas fracturing.

At present, the conductivity of the fracture network formed by shale gas fracturing is mostly described qualitatively, and there is a lack of suitable experimental equipment and methods for quantitative analysis. Lu Zhanguo and others carried out experimental research on the seepage characteristics in the orthogonal fracture network, and studied the influence of the seepage characteristics and model structure on the permeability in the orthogonal fracture network model, and established orthogonal fracture network models with different structures by using marble and stainless steel gaskets , and studied the seepage characteristics of water phase and oil-water two-phase through physical simulation. But its research object is fractured reservoir, and the influence of fracture network on the seepage velocity of liquid phase is considered. The results of some existing theoretical methods for evaluating the conductivity of fracture networks cannot be verified by experiments, and their accuracy cannot be guaranteed. The network fractures formed by shale gas fracturing are often filled with proppant. There are currently no experimental equipment and methods for quantitative research on this complex network of sand-filled fractures. The backwardness of evaluation methods has affected the progress of shale gas fracturing technology and the efficient development of shale oil and gas reservoirs.

Contents of the invention

Aiming at the above technical deficiencies, the present invention provides a device for testing the conductivity of a shale gas fracture network to simulate and measure the conductivity of a fracture network produced by fracturing a shale reservoir.

The present invention also provides a working method of the above device.

Technical scheme of the present invention is as follows:

A device for testing the conductivity of a shale gas fracture network, which includes a rectangular diversion chamber, a gas flow meter, a differential pressure gauge and a displacement meter; the diversion chamber includes a side wall, an upper piston and a The lower piston, the diversion cavity enclosed by the side wall, the upper piston and the lower piston, an upper cover plate is installed on the upper piston, and a lower cover plate is installed under the lower piston, in the diversion cavity and in the Marbles simulating shale cracks are arranged between the upper piston and the lower piston, and rubber rings are respectively arranged on the upper edge and the lower edge of the side wall; the purpose of the rubber rings is to seal the diversion chamber;

An air inlet and an air outlet are respectively provided on the side walls of the left and right ends of the diversion chamber, the air inlet is connected to the gas source through a pipeline, and a gas flow meter is arranged on the pipeline;

The diversion chamber is installed on the press, and a displacement meter a and a displacement meter b are arranged at the left and right ends of the diversion chamber and between the upper cover and the lower cover; the press The pressure provided for the diversion chamber is used to simulate the closure pressure of fractures in the formation; when the press pressurizes the diversion chamber, the displacement meter displays the effective fracture width of the fracture network in the diversion chamber in real time, and records Effective fracture width of the fracture network at each closure pressure.

An inlet pressure detection port and an air outlet pressure detection port are arranged on the side wall of the front end of the diversion chamber, and a differential pressure gauge is arranged between the inlet pressure detection port and the outlet pressure detection port.

Preferably, according to the present invention, the marble is covered with a proppant anti-flow net. The proppant anti-flow net is used to prevent the proppant from flowing out from the simulated shale fracture network.

Preferably according to the present invention, the gas source is bottled nitrogen.

Preferably, according to the present invention, the upper cover plate and the lower cover plate are both steel plates.

Preferably according to the present invention, the device for testing the conductivity of the shale gas fracture network also includes a data acquisition and control system and a computer, and the gas flow meter, differential pressure meter, displacement meter a and displacement meter b pass through the The above data acquisition and control system is connected with the computer.

Preferably according to the present invention, the marble for simulating shale cracks is prepared from a whole block of marble according to the following processing method:

(1) Select a monolithic marble with a length of 178 mm, a width of 37 mm, and a thickness ranging from 0.4 mm to 1.5 mm, and the wettability of the monolithic marble is the same as that of the shale to be simulated;

(2) According to the size of the shale fracture network to be simulated, the whole block of marble described in step (1) is cut horizontally and vertically, and then loaded into the diversion chamber.

A method for testing the conductivity of a shale gas fracture network by using the above-mentioned device, comprising the following steps:

(1) Add proppant to the diversion chamber according to a certain sand concentration to realize the effective fracture width of different fracture networks. The total amount of proppant added divided by the cross-sectional area of the diversion chamber is the initial effective fracture width of the fracture network;

(2) Open the data acquisition and control system;

(3) Start the press, set the pressure of the press, and apply pressure to the guide chamber, and the applied pressure range is 0-100MPa;

(4) Open the air source to ventilate the guide chamber, and start the experiment after the differential pressure gauge remains stable;

(5) Turn on the computer, and transmit the collected gas flow Q, differential pressure data ΔP and displacement data h to the computer through the data acquisition and control system;

(6) The computer calculates the effective fracture width and the simulated shale gas fracture network conductivity k _f w _f under constant pressure based on the gas flow Q, pressure difference data ΔP and displacement data h collected in real time into formula ①

$k_f{w}_f=\frac{\mathrm{Q\μ\ΔL}}{\mathrm{A\ΔP}}$ ①

w _f in formula ①—the effective fracture width, which is the ratio of the total volume of the actual fractures in the simulated fracture network to the cross-sectional area of the diversion chamber, k _f —the permeability of the simulated shale fracture network; Q -The flow rate of gas flowing through the diversion chamber, which is read by the gas flow meter; μ—the viscosity of _N at normal temperature; ΔL—the length of the diversion chamber; Multiply the effective fracture width of the simulated shale fracture marble fracture network; ΔP—the pressure difference of the gas flowing through the diversion chamber, which is read by the differential pressure gauge;

(7) Change the pressure of the press, and repeat steps (3) to (6); the purpose of this step is to test simulated shale gas fractures under different closure pressures of fractures in the formation under the same initial effective fracture width Network diversion capability;

(8) Change the amount of proppant added or sanding concentration, and repeat steps (1) to (7); the purpose of this step is to test the simulation page under different closure pressures of fractures in the formation under different initial effective fracture widths Conductivity of rock-gas fracture network.

Beneficial effects of the present invention:

1. The present invention fills up the gap that the conductivity of the shale gas fracture network cannot be measured by experimental means, and can measure the conductivity under different fracture network models; the diversion chamber described in the present invention is different from the traditional API standard guide Flow chamber: The end of the traditional API standard diversion chamber is arc-shaped, but the end of the diversion chamber of the present invention is square, its volume is 6 times that of the traditional API standard diversion chamber, and it can realize the diversion capacity of complex crack networks Research;

2. The present invention proposes the use of marble slabs to simulate shale, which overcomes the difficulties and high costs of on-site shale coring, and greatly reduces the difficulty and cost of experiments;

3. The present invention can assemble the model of various crack networks through the free cutting of marble, and increase the manual adjustment of the experiment;

4. The structure of the device described in the present invention is simple and easy to operate, and the experimental method provided is practical, and the conductivity of the fracture network of the shale gas reservoir has been successfully measured.

Description of drawings

Fig. 1 is a schematic structural view of a device for testing the conductivity of a shale gas fracture network according to the present invention;

Fig. 2 is a schematic structural view of the diversion chamber of the present invention;

Fig. 3 is the structural representation of the marble of simulating shale fracture network of the present invention;

In Fig. 1-3, 1, gas source; 2, gas flow meter; 3, displacement meter a; 4, displacement meter b, 5, differential pressure meter; 6, data acquisition and control system; 7, computer; 8, Press; 9. Diversion chamber; 10. Propant anti-flow net; 11. Upper cover plate; 12. Lower cover plate; 13. Upper piston; 14. Lower piston; 15. Marble for simulating shale cracks; 16. Inlet pressure detection port; 17, air outlet pressure detection port; 18, air inlet; 19, air outlet; 20, apron; 21, proppant; 22, crack;

Detailed ways

The present invention will be described in detail below in conjunction with the embodiments and the accompanying drawings, but is not limited thereto.

Embodiment 1,

A device for testing the conductivity of a shale gas fracture network, which includes a rectangular diversion chamber 9, a gas flow meter 2, a differential pressure gauge 5, a displacement meter a, and a displacement meter b; the diversion chamber 9 includes side walls, The diversion chamber is provided with an upper piston 13 and a lower piston 14, and the side wall, the upper piston 13 and the lower piston 14 are closed to form a diversion chamber, an upper cover plate 11 is installed on the upper piston 13, and a lower piston 14 is installed. There is a lower cover plate 12, a marble 15 for simulating shale cracks is arranged in the diversion cavity and between the upper piston 13 and the lower piston 14, and glue is arranged on the upper edge and the lower edge of the side wall respectively. Circle 20;

An air inlet 18 and an air outlet 19 are respectively provided on the side walls of the left and right ends of the diversion chamber 9. The air inlet 18 is connected to the gas source 1 through a pipeline, and a gas flow meter 2 is arranged on the pipeline. ;

The diversion chamber 9 is installed on the press 8, and a displacement meter a and a displacement meter b are arranged at the left and right ends of the diversion chamber 9 and between the upper cover plate 11 and the lower cover plate 12; The press 8 provides pressure for the diversion chamber 9 to simulate the closing pressure of the fracture in the formation; when the press 8 pressurizes the diversion chamber 9, the displacement meter displays the diversion in real time Indoor fracture network effective fracture width, respectively record the effective fracture width of the fracture network under each closure pressure.

An inlet pressure detection port 16 and an outlet pressure detection port 17 are arranged on the side wall of the front end of the diversion chamber, and a differential pressure gauge 5 is arranged between the inlet pressure detection port 16 and the outlet pressure detection port 17 .

The marble 15 for simulating shale cracks is prepared by the following processing method from a whole block of marble:

(1) Select a monolithic marble with a length of 178 mm, a width of 37 mm, and a thickness ranging from 0.4 mm to 1.5 mm, and the wettability of the monolithic marble is the same as that of the shale to be simulated;

(2) According to the size of the shale fracture network to be simulated, the whole block of marble described in step (1) is cut horizontally and vertically, and then loaded into the diversion chamber 9 .

Embodiment 2,

As shown in Figure 1-3.

A device for testing the conductivity of a shale gas fracture network as described in Example 1, the difference is that the device for testing the conductivity of a shale gas fracture network also includes a data acquisition and control system and a computer, the The gas flow meter, differential pressure meter, displacement meter a and displacement meter b are respectively connected to the computer through the data acquisition and control system.

The outside of the marble is covered with a proppant anti-flow net 10 . The gas source 1 is bottled nitrogen. Both the upper cover plate 11 and the lower cover plate 12 are steel plates.

Embodiment 3,

A method for testing the conductivity of a shale gas fracture network using the device described in Example 2, comprising the following steps:

A method for testing the conductivity of a shale gas fracture network by using the above-mentioned device, comprising the following steps:

(1) Add proppant to the diversion chamber according to a certain sand concentration to realize the effective fracture width of different fracture networks. The total amount of proppant added divided by the cross-sectional area of the diversion chamber is the initial effective fracture width of the fracture network;

(2) Open the data acquisition and control system;

(3) Start the press, set the pressure of the press, and apply pressure to the guide chamber, and the applied pressure range is 0-100MPa;

(4) Open the air source to ventilate the guide chamber, and start the experiment after the differential pressure gauge remains stable;

(5) Turn on the computer, and transmit the collected gas flow Q, differential pressure data ΔP and displacement data h to the computer through the data acquisition and control system;

(6) The computer calculates the effective fracture width and the simulated shale gas fracture network conductivity k _f w _f under constant pressure based on the gas flow Q, pressure difference data ΔP and displacement data h collected in real time into formula ①

$k_f{w}_f=\frac{\mathrm{Q\μ\ΔL}}{\mathrm{A\ΔP}}$ ①

w _f in formula ①—the effective fracture width, which is the ratio of the total volume of the actual fractures in the simulated fracture network to the cross-sectional area of the diversion chamber, k _f —the permeability of the simulated shale fracture network; Q -the flow rate of gas flowing through the diversion chamber, which is read by the gas flow meter; μ—the viscosity of _N at normal temperature; ΔL—the length of the diversion chamber; Multiply the effective fracture width of the simulated shale fracture marble fracture network; ΔP—the pressure difference of the gas flowing through the diversion chamber, which is read by the differential pressure gauge;

(7) change the pressure of described press, repeat steps (3)～(6);

(8) Change the amount of proppant added or the sanding concentration, and repeat steps (1) to (7);

Carry out the above steps (1) to (8), respectively record the initial effective fracture width size of the simulated shale gas fracture network, and the closure pressure value of the fracture in the press simulation layer, and calculate the corresponding simulation page according to the measured data according to formula ① The conductivity k _f w _f of the rock-gas fracture network is shown in Table 1:

Table 1:

Simulated shale fractures and marble cracks under different initial effective fracture widths (1.2mm, 1.6mm and 2.0mm) and different formation pressures

The drainage capacity of the seam network

Claims (5)

1. test a device for shale gas checking seam network flow conductivity, it is characterized in that, it comprises rectangular guiding room, gas flowmeter, differential manometer and displacement meter; Described diversion chamber comprises sidewall, in diversion chamber, is provided with upper piston and lower piston, described sidewall, upper piston and lower piston close surround diversion cavity, upper cover plate is installed on upper piston, under lower piston, lower cover is installed, in diversion cavity and between described upper piston and lower piston, be provided with the marble in simulation shale crack, be respectively arranged with cushion rubber at the top edge of described sidewall and lower limb;

The sidewall at the two ends, left and right of diversion chamber is respectively arranged with air inlet port and gas outlet, and described air inlet port is connected with source of the gas by pipeline, and described pipeline is provided with gas flowmeter;

Described diversion chamber is arranged on press, is provided with displacement meter a and displacement meter b at the two ends, left and right of diversion chamber between described upper cover plate and lower cover;

The sidewall of the front end of diversion chamber is provided with admission pressure and detects mouth and outlet pressure detection mouth, admission pressure detects between mouth and outlet pressure detection mouth and is provided with differential manometer; Cover in described marble outside and be provided with the anti-drift net of proppant; The device of described test shale gas checking seam network flow conductivity also comprises acquisition and control system and computer, and described gas flowmeter, differential manometer, displacement meter a are connected with computer respectively by described acquisition and control system with displacement meter b.

2. a kind of device testing shale gas checking seam network flow conductivity according to claim 1, it is characterized in that, described source of the gas is bottled nitrogen.

3. a kind of device testing shale gas checking seam network flow conductivity according to claim 1, it is characterized in that, described upper cover plate and lower cover are steel plate.

4. a kind of device testing shale gas checking seam network flow conductivity according to claim 1, it is characterized in that, the marble in described simulation shale crack is prepared according to following processing method by monoblock marble:

(1) choose the monoblock marble that length is 178mm, width is 37mm, thickness range is 0.4mm ~ 1.5mm, described monoblock marble wetability is identical with the shale that will simulate;

(2) according to the shale fracture network size that will simulate, the monoblock marble described in step (1) is carried out transverse cuts and longitudinally cutting, then load in diversion chamber.

5. utilize a method for device to test shale gas fracture network flow conductivity as claimed in claim 1, it is characterized in that, it is as follows that it comprises step:

(1) add proppant by certain sanding concentration to water conservancy diversion indoor, the effective seam realizing different fracture network is wide, and the initial effectively seam that the proppant total amount added is fracture network divided by the cross-sectional area of diversion chamber is wide;

(2) acquisition and control system is opened;

(3) start press, set the pressure of described press, exert pressure to diversion chamber, the scope of exerting pressure is 0-100MPa;

(4) open source of the gas to the indoor ventilation of water conservancy diversion, after described differential manometer maintenance is stable, starts experiment;

(5) open computer, by acquisition and control system, the gas flow Q collected, pressure difference data Δ P and displacement data h are transferred in computer;

(6) computer according to Real-time Collection to gas flow Q, pressure difference data Δ P and displacement data h bring formula into and 1. calculate simulation shale gas fracture network flow conductivity k under the wide and fixation pressure of effectively seam _fw _f

$k_f{w}_f=\frac{\mathrm{Q\μ\ΔL}}{\mathrm{A\ΔP}}$ ①

Formula 1. in w _f-effectively seam is wide, and described effective seam is wide is the ratio of the cumulative volume in actual crack and the cross-sectional area of diversion chamber in simulation fracture network, k _fthe permeability of-simulation shale fracture network; Q-gas flow, through the flow of diversion chamber, is read by gas flowmeter; N under μ-normal temperature ₂viscosity; The length of Δ L-diversion chamber; The flow section area of A-marble blocks: be multiplied by simulation shale crack marble fracture network by the width of diversion chamber and effectively stitch wide trying to achieve; Δ P-gas flow, through the pressure reduction of diversion chamber, is read by described differential manometer;

(7) change the pressure of described press, repeat step (3) ~ (6);

(8) change the amount or the sanding concentration that add proppant, repeat step (1) ~ (7).