CN111693455A - Drilling fluid mud cake generation test method - Google Patents

Abstract

The invention relates to a test method for drilling mud cake generation. The method includes: placing an oil separator on the outer periphery of the test rock sample, and filling the annulus between the oil separator and the test rock sample with filler; forming a confining pressure oil between the confining pressure cylinder and the oil separator accommodating cavity; one end of the test rock sample is fixed, and the other end is loaded with axial stress to a preset value; by injecting oil into the confining pressure oil accommodating cavity, the oil separator can form an internal and external pressure difference; The peripheral wall of the cylinder is subjected to radial stress to a preset value to simulate the horizontal in-situ stress of the formation at different depths; the drilling fluid is injected into the drilling fluid holding cavity formed by the internal annulus of the test rock sample and the stress is applied to the set stress value; The environment of the test rock sample is heated to a preset temperature; the process of forming the mud cake of the drilling fluid is observed or recorded. The invention can better restore the process of the drilling fluid filtrating to generate mud cake during the drilling process, and can provide a powerful theoretical basis for exploring the problem of wellbore instability.

Description

A kind of test method for drilling mud cake generation

technical field

The invention relates to the technical field of oil and gas well drilling engineering, in particular to a wellbore simulation mechanism and system for a drilling fluid mud cake generation test.

Background technique

During the drilling process, due to the penetration of the well wall, the drilling fluid will be filtrated, and the filtrate will enter the formation. In the process of drilling fluid filtration, a certain thickness of mud cake is formed on the surface of the well wall due to the accumulation of solid particles in the drilling fluid. The mud cake of the drilling fluid plays an extremely important role in controlling the filtration of the drilling fluid and maintaining the stability and lubrication of the well wall. effect. After a filter cake is formed on the wellbore, the permeability decreases, preventing or slowing down the further intrusion of drilling fluid into the formation. During the drilling process, the filtrate loss of the drilling fluid is inevitable, and the filter cake can be formed to protect the well wall through the filtration loss. Therefore, the formation of mud cake is of great significance to prevent the water phase in drilling fluid from invading the formation and maintain the stability of the wellbore.

The fluid loss of the drilling fluid is closely related to the permeability of the formation. The medium and deep hard brittle mud shale matrix in the Bozhong area has extremely low permeability, and there are near-horizontal bedding in the mud shale. Numerous micro-fractures provide drilling fluids. The water phase in the drilling fluid enters the formation through micro-fractures as seepage channels. The seepage of the drilling fluid may cause the drilling fluid to form a mud cake on the well wall, thereby preventing the seepage of the drilling fluid and preventing the water phase in the drilling fluid. Entering the formation causes hydration of the shale formation, leading to complex accidents such as wellbore instability. In recent years, in the face of the needs of exploration and development of oil and gas resources at home and abroad, the stratum conditions encountered have become more and more complex, and the problem of shale wellbore instability has become more and more complicated. The evaluation lacks in-depth understanding, and there is currently no experimental device and method for effectively simulating the real formation mudcake state.

During the drilling process, the mechanism of wellbore instability in hard and brittle mud shale has always been a hotly debated aspect in academics. Therefore, it is necessary to carry out laboratory tests to provide support for comprehensive theoretical analysis and numerical simulation research, especially to reveal hard and brittle mud shale wells. The mechanism of wall instability provides technical support for safe and rapid drilling.

SUMMARY OF THE INVENTION

The present invention aims to provide a mud cake generation test method for drilling fluid, so as to simulate the formation of mud cake in the drilling process and then evaluate the mud cake, thereby providing a reliable theoretical basis for the drilling process of deep fracture hard and brittle mud shale .

The present invention proposes a test method for drilling mud cake generation, the method comprising:

The oil separator is placed around the outer periphery of the test rock sample, and the annulus between the oil separator and the test rock sample is filled with fillers;

A confining oil accommodating cavity is formed between the confining pressure cylinder and the oil separator;

One end of the test rock sample is fixed, and the other end is loaded with axial stress to a preset value to simulate the vertical stress of the formation at different depths;

By injecting oil into the confining pressure oil accommodating cavity, the oil separator sleeve forms an internal and external pressure difference;

By applying radial stress to a preset value to the peripheral wall of the confining pressure cylinder to simulate the horizontal in-situ stress of the formation at different depths;

injecting drilling fluid into the drilling fluid accommodating cavity formed in the inner annulus of the test rock sample and applying stress to the set stress value;

heating the environment of the test rock sample to a preset temperature;

Observe or record the formation process of the mud cake of the drilling fluid.

According to an embodiment of the present invention, the compressive strength of the filler is greater than or equal to 60 MPa.

According to an embodiment of the present invention, the shape of the filler is spherical, and the filler is solid ceramsite.

According to an embodiment of the present invention, the size of the far field formation permeability is changed by changing the particle size of the filler.

According to an embodiment of the present invention, the drilling fluid stress in the drilling fluid accommodating cavity is controlled by an overflow control valve.

According to an embodiment of the present invention, the environment of the test rock sample is heated to a preset temperature by arranging a heating ring on the outer wall of the confining pressure cylinder.

According to an embodiment of the present invention, the top of the test rock sample is sealed with the oil separator, and the bottom of the test rock sample is sealed with the oil separator; the confining pressure oil accommodating cavity is in the A closed space is formed outside the grease trap.

According to an embodiment of the present invention, the test is controlled by monitoring the radial pressure inside the confining oil accommodating cavity and the axial pressure below the outside, and monitoring the temperature outside the upper end of the test rock sample. .

According to an embodiment of the present invention, oil is injected into the confining pressure accommodating cavity through a confining pressure oil pump, and the confining pressure oil pump and the confining pressure accommodating cavity form a circulation route for monitoring the confining pressure accommodating cavity Check whether the cavity is full of surrounding oil.

According to an embodiment of the present invention, the overflow valve is used to control the liquid column pressure of the drilling fluid.

The technical solution of the present invention can be used as a simulation test of the interaction between drilling fluid and formation, and can better restore the process of mud cake formation on the wellbore during the drilling process. The mud cake formed by the invention can be used to evaluate the characteristics of drilling fluid in formation wall-building performance, can better evaluate the plugging effect of the drilling fluid, and provides a solution for exploring the problem of wellbore instability caused by the interaction between the drilling fluid and the formation. solid theoretical foundation.

Description of drawings

1 is a schematic diagram of the overall structure of a drilling fluid mud cake quality test device according to an embodiment of the present invention;

2 is a schematic structural diagram of a wellbore simulation mechanism according to an embodiment of the present invention;

Fig. 3 is a top view of the wellbore simulation mechanism according to an embodiment of the present invention;

Reference number:

A Wellbore simulation mechanism, B temperature and pressure control device, C drilling fluid operation device, 1 support, 2 confining pressure cylinders, 3 axial loading plungers, 4 oil separators, 5 test rock samples, 6 ceramsites, 7 accommodating cavities , 8 sealing gaskets, 9 sealing gaskets, 10 pressure sensors, 11 pressure sensors, 12 pressure sensors, 13 confining pressure chambers, 15 axial loading bases, 16 axial loading piston pumps, 17 radial loading pistons Pump, 18 overflow control valve, 19 confining pressure oil pump, 20 drilling fluid piston pump, 21 flow control valve, 22 flow control valve, 23 flow control valve, 24 flow control valve, 25 temperature sensor, 26 control system, 27 confining pressure accommodating cavity base, 28 temperature loader, 29 bottom fixing piece, 30 top fixing piece, 31 pressure gauge, 32 flow control valve, 33 inner wall of confining pressure cylinder, 34 annular space.

Detailed ways

The preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings, so as to more clearly understand the objects, features and advantages of the present invention. It should be understood that the embodiments shown in the accompanying drawings are not intended to limit the scope of the present invention, but are only intended to illustrate the essential spirit of the technical solutions of the present invention.

The present invention conducts laboratory tests to reveal the instability mechanism of oil well walls, especially hard and brittle mud shale well walls, provides support for theoretical analysis and numerical simulation comprehensive research, and further provides technical support for safe and rapid drilling.

As shown in FIG. 1 , the system on which the test method of the present invention is based is mainly composed of a wellbore simulation mechanism A, a temperature and pressure control device B, and a drilling fluid operation device C.

For the test, a test rock sample 5 is prepared, and the inner hole of the test rock sample 5 forms a drilling fluid accommodating cavity 7 .

Among them, as shown in Figure 2, in order to simulate the topography of the oil well and the loss-taking process as realistically as possible, the wellbore simulation mechanism A proposed by the present invention mainly includes:

The stratum simulating filler 6 can be coaxially arranged outside the test rock sample 5 to simulate the far-field stratum. Considering the simulating stratum conditions of the filler, the compressive strength of the filler is preferably greater than or equal to 60MPa. Carrying out, the shape of the filler is preferably spherical, as the material for simulating the formation filler, such as solid ceramsite and the like.

The oil separator 4 can be coaxially arranged on the outermost side of the test rock sample 5 and the formation simulating packing, and is used to isolate the oil in the periphery from the wellbore mechanism. sample and top and bottom mounts.

The top fixing member 30 can be a spacer, and the top fixing member can be coaxially arranged on the top of the test rock sample 5; of course, the structure is not limited in this way.

The bottom fixing member 29 can be a block-type base, and the bottom fixing member is coaxially arranged at the bottom of the test rock sample for fixing the test rock sample;

The top gasket 9 can be arranged between the top block 30 and the test rock sample 5;

The bottom gasket 8 can be arranged between the bottom fixing member 29 and the test rock sample 5 .

Both the top gasket 9 and the bottom gasket 8 are provided with through holes in the center so as to communicate with the inner passages of the upper and lower fixing members.

The top gasket 9 and the bottom gasket 8 are used to seal the top and bottom of the test rock sample to prevent drilling fluid leakage.

Of course, the above components are not all necessary settings, and can be changed as needed.

The temperature and pressure control device B mainly includes:

The confining pressure cylinder 2 is arranged on the periphery of the wellbore simulation mechanism, and a confining pressure accommodating cavity is formed between the confining pressure cylinder and the wellbore simulating mechanism, so that oil can be injected into the confining pressure accommodating cavity to be compatible with the wellbore simulation mechanism. The pressure in the wellbore simulation mechanism forms a pressure differential for the simulation of drilling fluid injection;

The temperature loader 28 can be set as a heating ring, and the heating ring 28 is set on the outer circumference of the confining pressure cylinder 2 to heat the wellbore simulation mechanism as a whole (the heat can be conducted through the oil in the confining pressure accommodating cavity 13 ). ); of course, the heating device is not limited in this way;

Axially loaded plunger pump 16, the axially loaded plunger pump 16 is arranged at the bottom of the confining pressure cylinder 2 to load axial stress on the wellbore simulation mechanism;

The confining pressure oil pump 19, the confining pressure oil pump 19 can be connected to the confining pressure accommodating cavity 13 formed inside the confining pressure cylinder 2 at the upper and lower positions of the confining pressure cylinder 2 through the flow pipeline, and can be injected into the micro-pressure cavity 13 Oil, the flow line can be provided with flow control valves 21, 22, 23, 24;

The radially loaded plunger pump 17 is connected to the inner wall 33 of the confining pressure cylinder through a pressurized pipeline, and is used to apply radial stress to the wellbore simulation mechanism by squeezing the cylinder wall.

The axial loading plunger 3 is abutted on the top of the confining pressure cylinder 2 and is used for connecting and fixing with the bracket 1 so as to load axial stress.

The confining pressure cylinder base 27 is arranged on the upper end of the axial loading plunger pump 16 , the confining pressure cylinder base 27 is provided with a flow pipeline inside, and can be connected to the wellbore simulation mechanism through the axial loading base 15 Pass;

The axial loading base 15 can be arranged on the upper part of the confining cylinder base 27 .

The confining pressure cylinder can be designed with a cover on the top, a communication port on the cover, and an open bottom with a base, or a bottom on the bottom of itself, and the structure can be appropriately changed.

The bracket 1 can be used to support the entire temperature and pressure control device.

Of course, the above components are not all necessary settings, and can be changed as required.

The drilling fluid operation device C may include:

The drilling fluid pump 20 communicates with the drilling fluid accommodating cavity 7 through a flow line;

An overflow control valve 18, the overflow control valve 18 is arranged at the tail of the flow line connected to the drilling fluid pump 20, that is, downstream of the wellbore simulation mechanism, so as to control the pressure in the oil trap;

Flow control valve 32, the flow control valve 32 is arranged on the flow line between the drilling fluid pump 20 and the drilling fluid accommodating cavity 7;

The pressure gauge 31, the flow control valve 31 is arranged on the flow line between the drilling fluid pump 20 and the drilling fluid accommodating cavity 7.

Of course, the above components are not all necessary settings, and can be changed as needed.

The above system may further include a data collection mechanism, and the data collection mechanism may include:

a pressure sensor 10, the pressure sensor 10 can be arranged at the entrance of the drilling fluid accommodating cavity in the wellbore simulation mechanism, and is used for monitoring the pressure in the wellbore of the wellbore simulation mechanism;

a pressure sensor 11, the pressure sensor 11 can be arranged inside the confining pressure cylinder to monitor the magnitude of the applied radial stress;

a pressure sensor 12, the pressure sensor 12 can be arranged outside the axial loading base 15 for monitoring the magnitude of the applied axial stress;

a temperature sensor 25, the temperature sensor is arranged outside the wellbore simulation mechanism, and is used for monitoring the temperature of the wellbore simulation mechanism;

The pressure difference between the pressure sensor 10 and the pressure sensor 11 is the pressure difference of the filtration of drilling fluid.

The top fixing member 30 and the bottom fixing member 29 can be fixed on both ends of the test rock sample 5 by insulating heat shrinkable sleeves.

In the present invention, the permeability of the far field formation can be changed by changing the particle size of the filler of the simulated formation.

During the test, when the pressure gauge 31 shows an increase in pressure, the flow control valve 32 can be closed, the pressure control valve 25 can be opened, and the drilling fluid pressure in the drilling fluid accommodating chamber 7 can be applied through the pressure line.

The flow control valves 21, 22, 23, and 24 can be used to control the confining pressure oil to enter the confining pressure accommodating cavity. When the confining pressure accommodating cavity is full of confining pressure oil, the flow control valve 24 should be closed first. The remaining flow control valves 21, 22, 23 are closed again.

In the above solution, the pressure control of the present invention forms a quasi-triaxial pressure control system, the quasi-triaxial pressure control system includes: an axial pressure control system and a radial pressure control system, and the axial pressure control system mainly involves the axial pressure control system. Loading plunger pump 16 and confining pressure cylinder base 27 ; the radial pressure control system mainly involves confining pressure oil pump 19 , confining pressure cylinder 2 , radially loading plunger pump 17 and confining pressure cylinder base 27 .

Specifically, according to an embodiment of the present invention, when the above-mentioned system is used to perform the drilling fluid mud cake generation test, the following operations are mainly performed:

First, the test rock sample 5 is fixed with the outer edge insulating heat shrinkable sleeve (ie, the oil separator) 4, and an annular space is formed between the test rock sample 5 and the outer edge insulating heat shrinkable sleeve (ie the oil separator) 4, The outer edge insulating heat shrinkable sleeve 4 and the annular space of the test rock sample 5 are filled with ceramsite, and the test rock sample 5 is fixed by the top fixing member 30 and the bottom fixing member 29, and placed on the axial loading base 16 ;

Then, the pressure sensor 11 and the pressure sensor 12 are arranged on the inner side of the confining pressure cylinder 2 and the outer side of the axial loading base 15, respectively, while a temperature sensor 25 is arranged on the outer side of the top fixing member 30 of the wellbore simulation mechanism , and connect all the pressure sensors 11, pressure sensors (2 and temperature sensors 25 with the temperature and pressure control system 26 through data lines;

Then, the confining pressure cylinder 2 is lowered to the confining pressure cylinder base 27, and a confining pressure oil accommodating cavity 13 is formed between the confining pressure cylinder 2 and the wellbore simulation mechanism, which is used to store the confining pressure oil and is convenient for applying radial stress ;

After that, the confining oil pump 19 is injected into the confining oil accommodating chamber 13 through the flow line, and the flow control valve 21, the flow control valve 22, the flow Control valve 23 and flow control valve 24 to control the oil pressure in the confining oil accommodating chamber;

After that, the axial loading plunger pump 16 in the temperature and pressure control system is turned on, and the axial stress is applied to the wellbore simulation mechanism to a preset value through the axial loading plunger pump 16 to simulate the formation in Vertical stress at different depths, turn on the radially loaded plunger pump 17 in the temperature and pressure control system, and apply radial stress to the confining pressure cylinder 2 to a preset value through the radially loaded plunger pump 17 In order to simulate the horizontal in-situ stress of the formation at different depths, while the radial stress is loaded by the radial loading plunger pump, the drilling fluid piston pump 20 is used to drill into the inner annulus of the test rock sample. The drilling fluid is injected into the fluid holding chamber 7 and stress is applied to the stress set by the overflow control valve 32, and the heating ring 28 is opened at the same time to heat the wellbore simulation mechanism to a preset temperature;

After that, the control system 26 collects the test data measured by the pressure sensor 11, the pressure sensor 12 and the temperature sensor 25 in real time;

Afterwards, after the drilling fluid operation system circulates the drilling fluid for a period of time, the test equipment is dismantled, the test rock sample is taken out to observe the inner annular well wall of the test rock sample, and the test data is saved.

Optionally, the method further includes the steps of: closing the temperature and pressure control mechanism, decompressing the confining pressure accommodating chamber 2, the drilling fluid operating system, and the axial and radial loading respectively, and disassembling and evaluating the hard and brittle mud sheets. The test device for the mud cake quality of rock formation drilling fluid recovers the pressure sensor and the temperature sensor, and discards the outer edge insulating heat shrinkable sleeve and the ceramsite together.

Optionally, the above steps are repeated to measure the quality of drilling fluid and mud cake in hard and brittle mud shale formations under different drilling fluid types, densities, well depths, formation conditions, and temperatures and their changing laws.

Optionally, the drilling fluid is configured according to field data in the test preparation stage.

Optionally, a pressure gauge is installed on the flow line of the drilling fluid operation system to monitor pressure changes of the drilling fluid operation system.

Optionally, in the wellbore simulation mechanism, the diameter of the top and bottom fixing pieces should be the same as the diameter of the outer insulating heat shrinkable sleeve, and the top fixing piece and the bottom fixing piece should form a ring with the same size as the test rock sample. null.

Optionally, the wellbore simulation mechanism is sealed with an insulating gasket on the top of the test rock sample to prevent the drilling fluid from seeping into the ceramsite formation from the upper part, so as to ensure that the drilling fluid forms radial filtration in the wellbore.

Optionally, the wellbore simulation mechanism is sealed with an insulating gasket at the bottom of the test rock sample to prevent the penetration of drilling fluid.

Optionally, the confining pressure cylinder is fixedly supported by a bracket and a confining pressure cylinder base.

Optionally, four flow control valves are provided on the flow line connecting the confining pressure oil pump and the confining pressure cylinder to control the flow switch of the confining pressure oil pump.

Optionally, the drilling fluid pump and the confining pressure oil pump control flow and circulation through a flow control valve.

It should be noted that the above steps are not all necessary settings, and the sequence is not limited by this, and can be adjusted according to actual operations.

Example

As shown in Figure 1, the simulation test device for evaluating the mud cake quality of the hard and brittle mud shale formation provided by the present invention is mainly composed of a wellbore simulation mechanism, a temperature and pressure control device and a drilling fluid operation device.

As shown in Figures 2 and 3, the wellbore simulation structure includes: an insulating heat-shrinkable sleeve 4 coaxial with the test rock sample 5, a ceramsite 6 filled in the annular space between the test rock sample 5 and the coaxial heat-shrinkable sleeve 4, and the test rock The sealing gaskets 9 and 8 at the top and bottom of the sample, the top fixing member 30 and the bottom fixing member 29 are used to fix the test rock sample 5. A drilling fluid accommodating cavity 7 is formed in the inner hole of the test rock sample 5, and the accommodating cavity is communicated with the drilling fluid passages in the upper and lower fixing members to accommodate the drilling fluid. An annular space 34 is provided inside the bottom fixing member 29 .

The temperature and pressure control mechanism includes: a confining pressure cylinder 2, a confining pressure accommodating cavity 13 is formed in the confining pressure cylinder 2, an axial loading plunger 3, a confining pressure accommodating cavity base 27, an axial loading base 15, and an axial loading plunger Pump 16 , radial pressure loading plunger pump 17 , confining pressure oil pump 19 , flow control valve 21 , flow control valve 22 , flow control valve 23 , flow control valve 24 , temperature loader 28 . The bracket 1 can provide support and installation positioning for the upper and lower loading plungers and plunger pumps. The axial loading plunger 3 and the axial loading base 15 respectively contact the wellbore simulation mechanism at the upper and lower ends of the test rock sample 5 .

The confining pressure accommodating cavity 13 is filled with confining pressure oil, and the flow control valve 23 and the flow control valve 24 ensure that the flow quality in the confining pressure accommodating cavity remains unchanged, and the radial pressure plunger pump 17 applies pressure to the test rock sample. Stress to simulate formation horizontal stress. Vertical stress is applied to the test rock sample by an axial pressure plunger pump 16 .

As shown in FIG. 1 , the drilling fluid operation device includes: a drilling fluid piston pump 20 , an overflow control valve 18 , a flow control valve 32 , and a pressure gauge 31 .

The drilling fluid is injected into the drilling fluid accommodation cavity 7 in the inner hole of the test rock sample through the drilling fluid pump 20, and the drilling fluid column pressure is applied through the drilling fluid pump 20 to form a pressure difference between the wellbore and the formation.

Preferably, the device further includes a data control system, and the data control system includes: a pressure sensor and a temperature sensor. The pressure sensor includes an axial pressure sensor and a radial pressure sensor, which are respectively arranged at the base of the confining pressure cylinder and the inside of the confining pressure accommodating cavity; the temperature sensor is connected to the outside of the top cushion block through a pipeline. Through the data control system, the axial loading stress, radial loading stress and loading temperature are precisely controlled to achieve the effect of simulating the formation.

Preferably, the formation simulation mechanism adopts the addition of ceramsite to the outside of the test rock sample to form a high-permeability formation for storing drilling fluid filtrate.

Preferably, the wellbore simulation mechanism is sealed with an insulating gasket at the top of the test rock sample to prevent the drilling fluid from leaking from the upper part and ensure that the drilling fluid forms radial filtration in the wellbore.

Preferably, the wellbore simulation mechanism is sealed with an insulating gasket at the bottom of the test rock sample to prevent the leakage of drilling fluid from the bottom and ensure that the drilling fluid forms radial filtration in the wellbore.

Preferably, the confining pressure oil pump forms a cycle with the confining pressure accommodating cavity to monitor whether the confining pressure accommodating cavity is full of confining pressure oil.

Preferably, the wellbore is isolated from the outside world, and the drilling fluid pump cannot form a circulation with the wellbore, and overflows through the overflow valve to control the pressure of the drilling fluid column, and form an internal and external pressure difference with the confining pressure accommodating cavity, which is the drilling fluid Fluid loss provides pressure conditions.

Preferably, the axial pressure control system and the radial pressure control system are fixed by a bracket and a base.

It should be noted that, in this document, relational terms such as "first" and "second" etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply these There is no such actual relationship or sequence between entities or operations. Moreover, the terms "comprising", "comprising" or any other variation thereof are intended to encompass a non-exclusive inclusion such that a process, method, article or device that includes a list of elements includes not only those elements, but also includes not explicitly listed or other elements inherent to such a process, method, article or apparatus. Without further limitation, an element qualified by the phrase "comprising a..." does not preclude the presence of additional identical elements in a process, method, article or apparatus that includes the element.

The above-mentioned embodiments are only used to illustrate the present invention, and the various parts and devices of the embodiments can be changed to some extent, and each embodiment can be combined or deleted as required, and not all components in the accompanying drawings are necessary. However, the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to these embodiments described herein, and all equivalent transformations and improvements based on the technical solutions of the present invention should not be excluded from the protection scope of the present invention.

Claims (10)

1. A drilling fluid mud cake generation test method is characterized by comprising the following steps:

placing an oil separation sleeve on the outer periphery of a test rock sample, and filling filler in an annular space between the oil separation sleeve and the test rock sample;

a confining pressure oil accommodating cavity is formed between the confining pressure cylinder and the oil separating sleeve;

fixing one end of the test rock sample, and loading axial stress to a preset value to simulate vertical stress of the stratum at different depths;

oil liquid is injected into the confining pressure oil containing cavity to enable the oil separation sleeve to form internal and external pressure difference;

applying radial stress to the peripheral wall of the confining pressure cylinder to a preset value to simulate horizontal ground stress of the stratum at different depths;

injecting drilling fluid into a drilling fluid containing cavity formed by the annular space inside the test rock sample and applying stress to a set stress value;

heating the environment of the test rock sample to a preset temperature;

observing or recording the process of the formation of the mud cake of the drilling fluid.

2. The drilling fluid mud cake formation test method of claim 1, wherein the compressive strength of the filler is greater than or equal to 60 MPa.

3. The drilling fluid mud cake formation test method of claim 1 or 2, wherein the filler is spherical and solid ceramsite.

4. The drilling fluid mud cake formation test method of claim 1 or 2, wherein the magnitude of far field formation permeability is varied by varying the particle size of the filler.

5. The drilling fluid mud cake formation test method of claim 1 or 2, wherein drilling fluid stress in the drilling fluid containment chamber is controlled by an overflow control valve.

6. The drilling fluid mud cake formation test method as claimed in claim 1 or 2, wherein the environment of the test rock sample is heated to a preset temperature by arranging a heating ring on the outer wall of the confining pressure cylinder.

7. The drilling fluid mud cake formation test method of claim 1 or 2, wherein the top of the test rock sample is sealed to the oil jacket and the bottom of the test rock sample is sealed to the oil jacket; the confining pressure oil accommodating cavity forms a closed space outside the oil separation sleeve.

8. A drilling fluid mud cake formation test method as claimed in claim 1 or 2, wherein the test is controlled by monitoring the radial pressure above the inside of the containment oil chamber and the axial pressure below the outside of the containment oil chamber, and by monitoring the temperature outside the upper end of the test rock sample.

9. The drilling fluid mud cake generation test method according to claim 1 or 2, wherein oil is injected into the confining pressure accommodating cavity through a confining pressure oil pump, and the confining pressure oil pump and the confining pressure accommodating cavity form a circulation path for monitoring whether the confining pressure accommodating cavity is filled with the confining pressure oil or not.

10. A drilling fluid mud cake formation test method according to claim 1 or 2, characterized in that overflow is performed through an overflow valve for controlling the fluid column pressure of the drilling fluid.

Images