Patent Publication Number: US-2023141812-A1

Title: Dynamic crack leaking stoppage evaluation experiment device and experiment method

Description:
FIELD OF THE INVENTION 
     The present disclosure relates to the technical field of petroleum engineering, in particular to a dynamic crack leaking stoppage evaluation experiment device and an experiment method thereof. 
     BACKGROUND OF THE INVENTION 
     In the field of petroleum engineering, well leakage has always been a world-class problem that has plagued domestic and international petroleum exploration and development and has not been completely resolved so far. Most of well drilling processes have different extents of leakage. Severe well leakage would cause drop of borehole pressure, affect normal well drilling, cause instability of well walls, and induce formation fluids to flow into the wellbore and result in well blowout. It has been indicated according to field experience that a success rate of leaking stoppage is less than 30%. 
     At present, a large number of researchers have studied on different types of leakage problems, and have proposed various materials of leaking stoppage agents and have evaluated leaking stoppage effects of these leaking stoppage agents. However, existing devices and methods for evaluating leaking stoppage agent materials can only perform qualitative evaluation and analysis on cracks with fixed fracture sizes, but in actual well drilling processes where most of cracks are initially in a closed state, only upon the action of pressure difference of well drilling fluid, can the cracks expand gradually, and then can the leaking stoppage materials in the well drilling fluid enter the cracks and apply bridging-plugging on the cracks. In addition, existing crack leaking stoppage evaluation devices are incapable of monitoring leaking stoppage speed and determining leaking stoppage location in real time, so that they can neither evaluate performance of leaking stoppage materials, leaking stoppage effect, proportioning relationship among leaking stoppage agent materials, and lamination ability of a leaking stoppage layer, nor monitor and evaluate the leaking stoppage speed, the leaking stoppage effect and the leaking stoppage location in real time. 
     SUMMARY OF THE INVENTION 
     In view of the above problems, an objective of the present disclosure is to provide a dynamic crack leaking stoppage evaluation experiment device and an experiment method thereof, so as to solve the problem that the existing crack leaking stoppage evaluation device fails to conduct experiments due to incapable of simulating dynamic changes of morphology of a mud shale crack. 
     The present disclosure provides a dynamic crack leaking stoppage evaluation experiment device, which includes a crack simulation experiment instrument, a fluid reservoir tank, a recycle pool, a hydraulic pump, a hand pump, a fluid weighting electronic balance, an inlet pressure gauge, an outlet pressure gauge, a first back pressure back valve, and a second back pressure valve; an upper part of the crack simulation instrument is provided with a fluid inlet and a fluid outlet, and a bottom of the crack simulation instrument is provided with a fluid seepage port; a fluid outlet of the fluid reservoir tank is communicated with a fluid inlet of the hydraulic pump through a pipeline, and a fluid outlet of the hydraulic pump is communicated with a fluid inlet of the crack simulation instrument through an input pipeline; the inlet pressure gauge is provided on the input pipeline; a fluid outlet of the crack simulation experiment instrument is connected to upright an upper part of the recycle pool through an output pipeline, and a fluid outlet end of the output pipeline is provided with the first back pressure valve; the outlet pressure gauge is provided on the output pipeline; the fluid seepage port is provided with a drain pipe, and the second back pressure valve is provided on the drain pipe; the fluid weighing electronic balance is provided with a fluid weighing container which is arranged upright below an outlet of the drain pipe; the hand pump is communicated with an air inlet provided on a side wall of a cylinder body; when the hand pump supplies a pressure to a annular space formed between a rubber sleeve and the cylinder body, due to deformability of the rubber sleeve, the pressure input by the hand pump can smoothly transfer to a rock-mass sample to enable a radial pressure to be applied on the rock-mass sample. 
     Preferably, the crack simulation experiment instrument includes the cylinder body, an upper cover, a lower cover, an upper plug, a lower plug, an indenter, and the rubber sleeve; the upper cover and the lower cover are arranged at top and bottom ends of the cylinder body, respectively, the upper plug and the lower plug are arranged inside the cylinder body and closely attached to the upper cover and the lower cover, respectively; the upper plug, the lower plug and the cylinder body jointly enclose an accommodating cavity, a geometric size of which can properly accommodate the rock-mass sample; a fluid inlet and a fluid outlet are provided on both sides of the upper cover, respectively, a fluid inlet channel slot is provided between the fluid inlet and the accommodating cavity, and the fluid inlet channel slot sequentially passes through, from outside to inside, the upper cover and the upper plug that are on the side close to the fluid inlet; a fluid outlet channel slot is provided between the fluid outlet and the accommodating cavity, and the fluid outlet channel slot sequentially passes through, from inside to outside, the upper plug and the upper cover that are on the side close to the fluid outlet; a junction slot is provided between the fluid inlet channel slot and the fluid outlet channel slot of the upper plug, and the junction slot is communicated with the accommodating cavity. 
     Preferably, the crack simulation experiment instrument is equipped with a dynamic crack simulation mechanism which includes a rock-mass sample, a fixed plate, two seam plates, multiple sets of springs, and a sealing rubber sleeve; the rock-mass sample is provided with a hollow groove inside, and an upper part of the hollow groove is communicated with a fluid inlet channel of the dynamic crack simulation mechanism; the fixing plate is fixed on a side wall and a bottom of the hollow groove; the two seam plates are arranged symmetrically with respect to a center line of the hollow groove, bottom ends of the two seam plates are both pivotally connected to the fixing plate arranged at the bottom of the hollow groove, and top ends of the two seam plates both touch a top surface of the hollow groove; when the two seam plates are in a closed state, the top ends of the two seam plates splice with each other to form an inverted corner; the sealing rubber sleeve is laid on outer surfaces of the seam plates; the sealing rubber sleeve extends, from bottom to top, from the bottom ends of the seam plates to contact points between the top ends of the seam plates and the top surface of the hollow groove, so as to enable complete sealing of the seam plates from the rock-mass sample; center lines of the fluid inlet channel slot and the fluid outlet channel slot are located on one same line, and a line connecting the fluid inlet channel slot and the fluid outlet channel slot is communicated with the junction slot in a cross-shape pattern; the fluid seepage port is provided at the bottom of the lower cover, a fluid seepage channel is provided between the fluid seepage port and the accommodating cavity, and the fluid seepage channel sequentially penetrates middle parts of the lower plug and the lower cover; several sets of springs are arranged between the seam plates and the fixing plate arranged at the side wall of the hollow groove, each set of springs includes two springs located at an identical height, and ends of each spring are respectively fixed on the sealing rubber sleeve and the fixed plate; one of the seam plates is provided with a plurality of pressure measuring points at intervals, and each pressure measuring point is provided with a pressure sensor which extends to outside through a wire and is provided with a pressure sensor connector; after leaking stoppage slurry enters the hollow groove of the rock-mass sample from the fluid inlet channel of the dynamic crack simulation mechanism, the leaking stoppage slurry enters the inverted corner at the top ends of the two seam plates and expands the two seam plates apart from each other to rotate to both sides around the fixed plate, so as to dynamically simulate an aperture-gap cracking process. 
     Preferably, the rubber sleeve is provided at an inner wall of the cylinder body and at connections between the cylinder body and the upper plug, the lower plug, the rubber sleeve divides the cylinder body into two closed spaces, that are, respectively, an annular space formed between the rubber sleeve and the cylinder body and a space enclosed by the rubber sleeve, the upper plug and the lower plug; the side wall of the cylinder body is provided with an air inlet which is communicated with the annular space formed between the rubber sleeve and the cylinder body. 
     The present disclosure further discloses an experiment method for obtaining crack dynamic changes of a crack plugged with fluid medium, which adopts the above-mentioned dynamic crack leaking stoppage evaluation experiment device and includes steps of: 
     Step A, assembling a crack simulation instrument; 
     Step A1, assembling the rock-mass sample, the fixed plate, the two seam plates, the multiple sets of springs, and the sealing rubber sleeve into a dynamic crack simulation mechanism; 
     Step A2, installing the lower plug, the dynamic crack simulation mechanism, and the upper plug within the rubber sleeve in sequence to assemble them into the crack simulation instrument; and 
     Step A3, turning the upper cover and the lower cover to make the rock-mass sample generate an axial stress; 
     Step B, sealing the accommodating cavity, and setting valve values of the first back pressure valve and the second back pressure valve and a flow rate of the hydraulic pump; 
     Step C, plugging a crack with clean water or leaking stoppage slurry to obtain dynamic change process of the crack; and 
     Step D, evaluating dynamic crack leaking stoppage effect, 
     wherein evaluation on the dynamic crack leaking stoppage effect includes quantitative evaluation on leaking stoppage location and dynamic pressure bearing capacity of the leaking stoppage slurry under scouring action of the leaking stoppage slurry, evaluation on an effect of fluid rheological parameters on stability of the second leaking stoppage layer after circulating fluid is replaced in the subsequent well drilling process, and evaluation an effect of hydraulic parameters of the leaking stoppage slurry on the stability of the second leaking stoppage layer. 
     Further, plugging a crack with clean water to obtain dynamic change process of the crack specifically includes steps of: 
     Step C11, activating the hydraulic pump so that clean water enters, via the fluid inlet, the crack simulation experiment instrument successively through the fluid reservoir tank, the hydraulic pump, and the input pipeline in sequence, wherein a portion of the clean water enters the crack by passing through the fluid inlet channel slot, the junction slot, and the fluid inlet channel and the inverted corner of the crack simulation mechanism, and then reaches the second back pressure valve by passing through the fluid seepage channel and the fluid seepage port; and wherein the other portion of the clean water reaches the first back pressure valve by passing through the fluid outlet channel slot, the fluid outlet and the output pipeline; 
     Step C12, forming, by the injected clean water, a hydraulic pressure gradually at the fluid inlet channel and the inverted corner; and 
     Step C13, expanding, when the hydraulic pressure exceeds an elastic force of the springs, the two seam plates apart from each other gradually, wherein as the hydraulic pressure at the fluid inlet channel and the inverted corner increases, an opening degree of the crack formed by expanding the two seam plates increases gradually until the hydraulic pressure exceeds a pressure value of 1.5 MPa set for the second back pressure valve, then the opening degree of the crack formed by the two seam plates changes no longer. 
     Further, plugging a crack with leaking stoppage slurry to obtain dynamic change process of the crack specifically includes steps of: 
     Step C21, filling the reservoir tank with leaking stoppage slurry; 
     Step C22, activating the hydraulic pump so that the leaking stoppage slurry in the reservoir tank enters, via the fluid inlet, the crack simulation instrument through the hydraulic pump and the input pipeline, wherein a portion of the leaking stoppage slurry enters the crack by passing through the fluid inlet channel slot, the junction slot, and the fluid inlet channel slot and the inverted corner of the crack simulation mechanism, and then reaches the second back pressure valve by passing through the fluid seepage channel and the seepage port; and wherein the other portion of the leaking stoppage slurry reaches the first back pressure valve by passing through the fluid outlet channel slot, the fluid outlet and the output pipeline; 
     Step C23, accumulating the leaking stoppage slurry gradually within the inverted corner to form a hydraulic pressure; 
     Step C24, expanding, when the hydraulic pressure at the inverted corner exceeds an elastic force of the springs, the two seam plates apart from each other gradually, wherein as the hydraulic pressure inside the crack simulation mechanism increases, an opening degree of a crack formed by expanding the two seam plates increases gradually until the hydraulic pressure exceeds a pressure value of 1.5 MPa set for the second back pressure valve, then the opening degree of the crack formed by the two seam plates changes no longer; at the same time, particles in the leaking stoppage slurry form a leaking stoppage layer in a channel of the crack; 
     Step C25, injecting the leaking stoppage slurry continuously into the fluid inlet channel and the inverted corner to form a hydraulic pressure which increases gradually, wherein under the action of the hydraulic pressure, the two seam plates are further expanded apart, so that the leaking stoppage layer is damaged or a location of the leaking stoppage layer is transferred, and a second leaking stoppage layer is newly formed; and 
     Step C26, recording change of a pressure value of the pressure sensor as a function of time, and recording, when it is observed that the pressure value of the pressure sensor changes suddenly, a position of a pressure measurement point on the seam plate that corresponds to the pressure sensor to determine leaking stoppage location of the leaking stoppage slurry in the crack. 
     Further, the quantitative evaluation on leaking stoppage location and dynamic pressure bearing capacity of the leaking stoppage slurry under scouring action of the leaking stoppage slurry is implemented after plugging the crack with the leaking stoppage slurry to obtain dynamic change process of the crack, and specifically includes steps of: 
     Step X1, adjusting, after a stable second leaking stoppage layer is formed, a pressure value of the first back pressure valve to be equal to a value of the inlet pressure gauge; 
     Step X2, leading the excess leaking stoppage slurry into the recycle pool through the first back pressure valve, so that the leaking stoppage slurry inside the fluid inlet channel and the inverted corner of the crack simulation mechanism forms a dynamic flow which causes continuous scour flow onto the leaking stoppage layer until the second leaking stoppage layer is damaged; 
     Step X3, subjecting the second leaking stoppage layer to damage gradually, so that the value of the inlet pressure gauge is varied and a width of the crack decreases; 
     Step X4, stopping, once a pressure at the fluid inlet channel and the inverted corner of the crack simulation mechanism is lower than the pressure value of the first back pressure valve, the leaking stoppage slurry dynamic flowing, plugging the crack once again, and then repeating the Steps X2 to X3; and 
     Step X5, recording change of the pressure value of the pressure sensor as a function of time, and recording, when it is observed that the pressure value of the pressure sensor changes suddenly, a position of a pressure measurement point on a seam plate that corresponds to the pressure sensor to determine leaking stoppage location of the leaking stoppage slurry in the crack. 
     Further, the evaluation on an effect of fluid rheological parameters on stability of the second leaking stoppage layer after circulating fluid is replaced in the subsequent well drilling process is implemented after plugging the crack with the leaking stoppage slurry to obtain dynamic change process of the crack, and specifically includes a step of: 
     Step Y, stopping, after a stable second leaking stoppage layer is formed, the hydraulic pump, and replacing the leaking stoppage slurry with clean water, water-based well drilling fluid or oil-based well drilling fluid, and adjusting the pressure value of the first back pressure valve to be equal to a value of the inlet pressure gauge that is before stopping the pump. 
     Further, the evaluation on an effect of hydraulic parameters on stability of the leaking stoppage slurry of the second leaking stoppage layer is implemented after plugging the crack with the leaking stoppage slurry to obtain dynamic change process of the crack, and specifically includes steps of: 
     Step Z1, adjusting, after a stable second leaking stoppage layer is formed, the pressure value of the first back pressure valve to be equal to a value of the inlet pressure gauge, and leading the excess leaking stoppage slurry into the recycle pool through the first back pressure valve so that the leakage leaking stoppage slurry inside the fluid inlet channel and the inverted corner of the crack simulation mechanism form a dynamic flow; 
     Step Z2, increasing a flow rate of the hydraulic pump to 3 L/min and keeping for 1 h; 
     Step Z3, increasing the flow rate of the hydraulic pump to 4 L/min and still keeping for 1 h; 
     Step Z4, increasing the flow rate of the hydraulic pump with an increment of 1 L/min per hour until the leakage stoppage layer is damaged; 
     Step Z5, recoding change of the pressure value of the pressure sensor as an function of time, and recording, when it is observed that the pressure value of the pressure sensor changes suddenly, a position of a pressure measurement point on a seam plate that corresponds to the pressure sensor to determine leaking stoppage location of the leaking stoppage slurry in the crack; and 
     Step Z6, plotting a curve regarding a relationship between the pressure value of the pressure measuring point on the seam plate and the flow rate. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a schematic diagram of a structure of a dynamic crack leaking stoppage evaluation experiment device according to Embodiment 1 of the present disclosure; 
         FIG.  2    is a cross-sectional view of a dynamic crack simulation mechanism provided in a crack simulation experiment instrument according to Embodiment 1 of the present disclosure; 
         FIG.  3    is a top view of the crack simulation experiment instrument according to Embodiment 1 of the present disclosure; 
         FIG.  4    is a front view of the crack simulation experiment instrument according to Embodiment 1 of the present disclosure; 
         FIG.  5    is a cross-sectional view along A-A in  FIG.  4   ; 
         FIG.  6    is a side view of the crack simulation experiment instrument according to Embodiment 1 of the present disclosure; 
         FIG.  7    is a cross-sectional view along B-B in  FIG.  6   ; 
         FIG.  8    is a longitudinal cross-sectional view of the dynamic crack simulation mechanism according to Embodiment 1 of the present disclosure; 
         FIG.  9    is a longitudinal cross-sectional view of inside of a hollow groove of the dynamic crack simulation mechanism according to Embodiment 1 of the present disclosure; and 
         FIG.  10    is a schematic diagram of the crack simulation experiment instrument installed on a fixing device according to Embodiment 1 of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     The following embodiments are used to illustrate the present disclosure, but are not intent to limit the protection scope of the present disclosure. 
     Embodiment 1 
     Provided in Embodiment 1 is a dynamic crack leaking stoppage evaluation experiment device, a structure of which is described in detail below. 
     Referring to  FIG.  1   , the experiment device includes a crack simulation experiment instrument  1 , a crack simulation experiment instrument fixing device  2 , a fluid reservoir tank  3 , a recycle pool  4 , a hydraulic pump  5 , a hand pump  6 , a fluid weighting electronic balance  7 , an inlet pressure gauge  8 , an outlet pressure gauge  9 , a first back pressure valve  10 , and a second back pressure valve  400 . 
     A fluid outlet of the fluid reservoir tank  3  is communicated with a fluid inlet of the hydraulic pump  5  through a pipeline, and a fluid outlet of the hydraulic pump  5  is communicated with a fluid inlet  31  of the crack simulation instrument  1  through an input pipeline  310 ; 
     The inlet pressure gauge  8  is provided on the input pipeline  310 ; 
     A fluid outlet  32  of the crack simulation experiment instrument  1  is connected to upright an upper part of the recycle pool  4  through an output pipeline  320 , and a fluid outlet of the output pipeline  320  is provided with the first back pressure valve  10 ; 
     The outlet pressure gauge  9  is provided on the output pipeline  320 ; 
     A drain pipe is provided in a fluid seepage port  36 , and the second back pressure valve  400  is provided on the drain pipe; 
     The fluid weighing electronic balance  7  is provided with a fluid weighing container which is arranged upright below an outlet of the drain pipe. The fluid weighing electronic balance  7  is configured to collect and weigh the fluid that enters the drain pipe from the fluid seepage port  36  and then flows out of the outlet of the drain pipe; 
     The hand pump  6  is communicated with an air inlet  38  provided on a side wall of a cylinder body  21 . 
     When the hand pump  6  supplies a pressure to a annular space formed between a rubber sleeve  27  and the cylinder body  21 , due to deformability of the rubber sleeve  27 , the pressure input by the hand pump  6  can smoothly transfer to a rock-mass sample  11  to enable a radial pressure to be applied on the rock-mass sample  11 . 
     Referring to  FIGS.  2  to  7   , the crack simulation experiment instrument  1  includes the cylinder body  21 , an upper cover  22 , a lower cover  23 , an upper plug  24 , a lower plug  25 , an indenter  26 , the rubber sleeve  27  and a sealing ring  28 . 
     The upper cover  22  and the lower cover  23  are arranged at top and bottom ends of the cylinder body  21 , respectively. The upper plug  24  and the lower plug  25  are arranged inside the cylinder body  21  and closely attached to the upper cover  22  and the lower cover  23 , respectively. The upper plug  24 , the lower plug  25  and the cylinder body  21  jointly enclose an accommodating cavity  20 , a geometric size of which can properly accommodate the rock-mass sample  11 , and a dynamic crack simulation mechanism is installed inside the accommodating cavity  20 . 
     Referring to  FIG.  8   , the dynamic crack simulation mechanism can dynamically simulate morphology change of a mud shale crack, and includes a rock-mass sample  11 , a fixed plate  12 , two seam plates  13 , multiple sets of springs  14 , and a sealing rubber sleeve  15 . 
     In this case, the rock-mass sample  11  is a mud shale sample in which a hollow groove  16  is provided inside, and an upper part of the hollow groove  16  is communicated with a fluid inlet channel  17  of the dynamic crack simulation mechanism; 
     The fixing plate  12  is fixed on the side wall and a bottom of the hollow groove  16 ; 
     The two seam plates  13  are arranged symmetrically with respect to the center line of the hollow groove  16 . Bottom ends of the two seam plates  13  are both pivotally connected to the fixing plate  12  arranged at the bottom of the hollow groove  16 , and top ends of the two seam plates  13  both touch a top surface of the hollow groove  16 . When the two seam plates  13  are in a closed state, the top ends of the two seam plates  13  splice with each other to just form an inverted corner  18 ; 
     The sealing rubber sleeve  15  is laid on outer surfaces of the seam plates  13 . The sealing rubber sleeve  15  extends, from bottom to top, from the bottom ends of the seam plates  13  to contact points between the top ends of the seam plates  13  and the top surface of the hollow groove  16 , so as to enable complete sealing of the seam plates  13  from the rock-mass sample  11 ; 
     Several sets of springs  14  are arranged between the seam plates  13  and the fixing plate  12  arranged at the side wall of the hollow groove  16 . Each set of springs  14  includes two springs  14  located at the same height. Ends of each spring  14  are respectively fixed on the sealing rubber sleeve  15  and the fixed plate  12 . A difficulty level that an aperture-gap cracks can be simulated by adjusting an elastic coefficient of the springs  14 . 
     After leaking stoppage slurry enters the hollow groove  16  of the rock-mass sample  11  from the fluid inlet channel  17  of the dynamic crack simulation mechanism, the leaking stoppage slurry enters the inverted corner  18  at the top ends of the two seam plates  13  and expands the two seam plates  13  apart from each other to rotate to both sides around the fixed plate  12 , so as to dynamically simulate an aperture-gap cracking process. 
     As a specific implementation, the several sets of springs  14  are arranged symmetrically about the center line of the hollow groove  16 . 
     Referring to  FIG.  9   , in order to enable real-time determination of leaking stoppage location and leaking stoppage speed, one of the seam plates  13  is provided with a plurality of pressure measuring points at intervals, each pressure measuring point is provided with a pressure sensor  19  which extends to the outside through a wire and is provided with a pressure sensor connector. 
     Preferably, the number of pressure measuring points is  4  to  6 . 
     Referring back to  FIGS.  2  to  7   , a fluid inlet  31  and a fluid outlet  32  are, respectively, provided on both sides of the upper cover  22 . A fluid inlet channel slot  33  is provided between the fluid inlet  31  and the accommodating cavity  20 , and the fluid inlet channel slot  33  sequentially passes through, from outside to inside, the upper cover  22  and the upper plug  24  that are on the side close to the fluid inlet  31 . A fluid outlet channel slot  34  is provided between the fluid outlet  32  and the accommodating cavity  20 , and the fluid outlet channel slot  34  sequentially passes through, from inside to outside, the upper plug  24  and the upper cover  22  that are on the side close to the fluid outlet  32 . A junction slot  35  is provided between the fluid inlet channel slot  33  and the fluid outlet channel slot  34  of the upper plug  24 , and the junction slot  35  is communicated with the accommodating cavity  20 . 
     Further, the fluid seepage port  36  is provided at a bottom of the lower cover  23 . A fluid seepage channel  37  is provided between the fluid seepage port  36  and the accommodating cavity  20 , and the fluid seepage channel  37  sequentially penetrates middle parts of the lower plug  25  and the lower cover  23 . 
     Further, the center lines of the fluid inlet channel slot  33  and the fluid outlet channel slot  34  are located on the same line, and a line connecting the fluid inlet channel slot  33  and the fluid outlet channel slot  34  is communicated with the junction slot  35  in a cross-shape pattern. 
     In order to ensure sealing performance of the accommodating cavity  20 , a sealing ring  28  is provided between an upper part of the cylinder body  21  and the upper cover  22 . 
     In order to further improve the sealing performance of the accommodating cavity  20 , a rubber sleeve  27  is provided at inner wall of the cylinder body  21  and at connections between the cylinder body  21  and the upper plug  24 , the lower plug  25 . The rubber sleeve  27  divides the cylinder body  21  into two closed spaces, that are, respectively, an annular space formed between the rubber sleeve  27  and the cylinder body  21  and a space enclosed by the rubber sleeve  27 , the upper plug  24  and the lower plug  25 . In this case, the upper plug  24  and the lower plug  25  are both rubber plugs. 
     Further, an indenter  26  is provided on the upper cover  22  in a threaded connection. Specifically, the upper cover  22  is provided with a groove, inner wall of the groove is provided with inner thread, and the indenter  26  is provided with outer thread. In the process of tightly screwing the indenter  26  onto the groove of the upper cover  22 , the indenter  26  acts on the upper plug to exert a force to the rock-mass sample  11 , so as to enable change of an axial stress to the rock-mass sample  11 . 
     Further, the cylinder body  21  is provided with through holes for arranging pressure sensor connectors of the pressure sensors  19  in a penetrating manner. A wire connecting a pressure sensor  19  and a pressure sensor connector is arranged to pass through a rubber plug which is provided in a through hole in a sealed manner. 
     Referring to  FIG.  10   , the crack simulation experiment instrument fixing device  2  includes a base  40 , a support rod  41 , a steel collar  43  and a screwing knob  42 . In this case, the support rod  41  is fixed on the base  40 . An outer shape of the crack simulation experiment instrument  1  is a cylinder. The steel collar  43  includes a ring part and a rod part, and the ring part of the steel collar  43  is sleeved on the outside of the crack simulation instrument  1 . The screwing knob  42  includes a fixedly connected screw part and a knob part, and outer wall of the screw part of the screwing knob  42  is provided with outer thread. A top end of the support rod  41  is provided with a hinge ring, and top side wall of the support rod  41  is provided with an inner threaded hole. The rod part of the steel collar  43  is hinged to the support rod  41 . The screw part of the screwing knob  42  is arranged inside the threaded hole on the top side wall of the support rod  41  and is fixedly connected to the rod part of the steel collar  43 . Tightening of the screwing knob  42  can implement adjustment and fixing of an angle of the crack simulation experiment instrument  1 . 
     Embodiment 2 
     Provided in Embodiment 2 is an experiment method for obtaining crack dynamic changes of a crack plugged with fluid medium, in which the dynamic crack leaking stoppage evaluation experiment device of Embodiment 1 is used and a method for obtaining the dynamic change process of a crack by plugging the crack with clean water or leaking stoppage slurry to promote dynamic changes of the crack is used. The experiment method specifically includes the following steps A to D: 
     Step A, assembling a crack simulation instrument  1 , which includes the following Steps A1 to A3: 
     Step A1, the rock-mass sample  11 , the fixed plate  12 , the two seam plates  13 , the multiple sets of springs  14 , and the sealing rubber sleeve  15  are assembled into a dynamic crack simulation mechanism; 
     Step A2, the lower plug  25 , the dynamic crack simulation mechanism, and the upper plug  24  are installed within the rubber sleeve  27  in sequence to assemble a crack simulation instrument  1 ; and 
     Step A3, the upper cover  22  and the lower cover  23  are turned to make the rock-mass sample  11  generate an axial stress; 
     Step B, sealing the accommodating cavity  20 , and setting valve values of the first back pressure valve  10  and the second back pressure valve  400  and a flow rate of the hydraulic pump  5 , which includes the following Steps B1 to B2: 
     Step B1, the hand pump  6  is activated to inject gas into an air inlet  38  on the side wall of the cylinder body  21  until a confining pressure of 10 MPa is formed within an annular space formed between the cylinder body  21  and the rubber sleeve  27 , so that sealing of the accommodating cavity  20  enclosed by the rock-mass sample  11 , the upper plug  24  and the lower plug  25  is formed; and 
     Step B2, a valve value of the first back pressure valve  10  is set to 4.5 MPa, a valve value of the second back pressure valve  400  is set to 1.5 MPa, and a flow rate of the hydraulic pump  5  is set to 2 L/min; 
     Step C, plugging a crack with clean water or leaking stoppage slurry to obtain dynamic change process of the crack; 
     In this case, said plugging a crack with clean water to obtain dynamic change process of the crack specifically includes the following steps C11 to C13: 
     Step C11, the hydraulic pump  5  is activated so that clean water enters, via the fluid inlet  31 , the crack simulation experiment instrument  1  successively through the fluid reservoir tank  3 , the hydraulic pump  5 , and the input pipeline  310  in sequence. A portion of the clean water enters the crack by passing through the fluid inlet channel slot  33 , the junction slot  35 , and the fluid inlet channel  17  and the inverted corner  18  of the crack simulation mechanism, and then reaches the second back pressure valve  400  by passing through the fluid seepage channel  37  and the fluid seepage port  36 . The other portion of the clean water reaches the first back pressure valve  10  by passing through the fluid outlet channel slot  34 , the fluid outlet  32  and the output pipeline  320 ; 
     Step C12, the injected clean water gradually forms a hydraulic pressure at the fluid inlet channel  17  and the inverted corner  18 ; and 
     Step C13, when the hydraulic pressure exceeds an elastic force of the springs  14 , the two seam plates  13  are gradually expanded apart from each other. As the hydraulic pressure at the fluid inlet channel  17  and the inverted corner  18  increases, an opening degree of a crack formed by expanding the two seam plates  13  increases gradually until the hydraulic pressure exceeds a pressure value of 1.5 MPa set for the second back pressure valve  400 , then the opening degree of the crack formed by the two seam plates  13  would not change any longer. 
     Through these above steps, control of the opening degree of the two seam plates  13  can be achieved by configuring a pressure value of the second back pressure valve  400 , so as to enable a dynamic crack simulation process. 
     In addition, said plugging a crack with leaking stoppage slurry to obtain dynamic change process of the crack specifically includes the following steps C21 to C26: 
     Step C21, the reservoir tank  3  is filled with leaking stoppage slurry; 
     Step C22, the hydraulic pump  5  is activated, so that the leaking stoppage slurry in the reservoir tank  3  enters, via the fluid inlet  31 , the crack simulation instrument  1  through the hydraulic pump  5  and the input pipeline  310 . A portion of the leaking stoppage slurry enters a crack by passing through the fluid inlet channel slot  33 , the junction slot  35 , and the fluid inlet channel  17  and the inverted corner  18  of the crack simulation mechanism, and then reaches the second back pressure valve  400  by passing through the fluid seepage channel  37  and the seepage port  36 . The other portion of the leaking stoppage slurry reaches the first back pressure valve  10  by passing through the fluid outlet channel slot  34 , the fluid outlet  32  and the output pipeline  320 ; 
     Step C23, the leaking stoppage slurry gradually accumulates within the inverted corner  18  to form a hydraulic pressure; 
     Step C24, when the hydraulic pressure at the inverted corner  18  exceeds an elastic force of the springs  14 , the two seam plates  13  are gradually expanded apart from each other. As the hydraulic pressure inside the crack simulation mechanism increases, an opening degree of the crack expanded by the two seam plates  13  gradually increases until the hydraulic pressure exceeds a pressure value of 1.5 MPa set for the second back pressure valve  400 , then the opening degree of the crack formed by the two seam plates  13  would not change any longer; at the same time, particles in the leaking stoppage slurry form a leaking stoppage layer  200  in a channel of the crack; 
     Step C25, the leaking stoppage slurry is continuously injected into the fluid inlet channel  17  and the inverted corner  18  to form a hydraulic pressure, and the hydraulic pressure increases gradually. Under the action of the hydraulic pressure, the two seam plates  13  are further expanded apart, so that the leaking stoppage layer  200  is damaged or a location of the leaking stoppage layer  200  is transferred, and a second leaking stoppage layer is newly formed; and 
     Step C26, change of a pressure value of the pressure sensor  19  is recorded as a function of time, when it is observed that the pressure value of the pressure sensor  19  changes suddenly, and a position of a pressure measurement point on the seam plate  13  that corresponds to the pressure sensor  19  is recorded to determine leaking stoppage location of the leaking stoppage slurry in the crack. 
     The foregoing steps are mainly used to simulate a leaking stoppage process in case of a dynamic crack and evaluate a variation range of the opening degree of the crack plugged by the leaking stoppage material. Leaking stoppage ability of the leaking stoppage material working on the dynamic crack can be quantitatively evaluated by means of a relationship of the pressure value of each pressure measurement point varying as a function of time. 
     Step D, evaluating dynamic crack leaking stoppage effect. 
     Evaluation on the dynamic crack leaking stoppage effect includes quantitative evaluation on leaking stoppage location and dynamic pressure bearing capacity of the leaking stoppage slurry under scouring action of the leaking stoppage slurry, evaluation on an effect of fluid rheological parameters on stability of the second leaking stoppage layer after circulating fluid is replaced in the subsequent well drilling process, and evaluation on an effect of hydraulic parameters of the leaking stoppage slurry on the stability of the second leaking stoppage layer. 
     In this case, the quantitative evaluation on leaking stoppage location and dynamic pressure bearing capacity of the leaking stoppage slurry under scouring action of the leaking stoppage slurry is implemented after plugging the crack with the leaking stoppage slurry to obtain dynamic change process of the crack, and specifically includes the following steps X1 to X5: 
     Step X1, after a stable second leaking stoppage layer is formed, a pressure value of the first back pressure valve  10  is adjusted to be equal to a value of the inlet pressure gauge  8 ; 
     Step X2, the excess leaking stoppage slurry will enter the waste fluid pool  4  (the recycle pool) through the first back pressure valve  10 , so that the leaking stoppage slurry inside the fluid inlet channel  17  and the inverted corner  18  of the crack simulation mechanism forms a dynamic flow, which will cause continuous scour flow onto the leaking stoppage layer  200  until the second leaking stoppage layer is damaged; 
     Step X3, the second leaking stoppage layer is gradually damaged, so that the value of the inlet pressure gauge  8  is varied and a width of the crack decreases; 
     Step X4, once a pressure at the fluid inlet channel  17  and the inverted corner  18  of the crack simulation mechanism is lower than the pressure value of the first back pressure valve  10 , the leaking stoppage slurry stops dynamic flowing and plugs the crack once again, and the steps X2 to X3 are repeated then; and 
     Step X5, change of a pressure value of the pressure sensor  19  is recorded as a function of time, when it is observed that the pressure value of the pressure sensor  19  changes suddenly, a position of a pressure measurement point on the seam plate  13  that corresponds to the pressure sensor  19  is recorded to determine leaking stoppage location of the leaking stoppage slurry in the crack. 
     By analyzing a relationship of the pressure value of each pressure measurement point varying as a function of time, the relationship is used to perform quantitative evaluation on the leaking stoppage location and the dynamic pressure bearing capacity of the leaking stoppage slurry working on the dynamic crack under an impact of scouring action of the leaking stoppage slurry. 
     The evaluation on an effect of fluid rheological parameters on stability of the second leaking stoppage layer after circulating fluid is replaced in the subsequent well drilling process is implemented after plugging the crack with the leaking stoppage slurry to obtain dynamic change process of the crack, and specifically includes: 
     Step Y, after a stable second leaking stoppage layer is formed, the hydraulic pump  5  is stopped, the leaking stoppage slurry is replaced with clean water, water-based well drilling fluid or oil-based well drilling fluid, and the pressure value of the first back pressure valve  10  is adjusted to be equal to a value of the inlet pressure gauge  8  that is before stopping the pump. 
     This approach is used to simulate a viscosity of circulating fluid, and carries out study on an effect on stability of the second leaking stoppage layer inside the dynamic crack, which is mainly used to evaluate the effect of rheological parameters, such as the viscosity of the fluid, on the stability of the second leaking stoppage layer after the circulating fluid is replaced in the subsequent well drilling process. 
     The evaluation on an effect of hydraulic parameters on stability of the leaking stoppage slurry of the second leaking stoppage layer is implemented after plugging the crack with the leaking stoppage slurry to obtain dynamic change process of the crack, and specifically includes: 
     Step Z1, after a stable second leaking stoppage layer is formed, the pressure value of the first back pressure valve  10  is adjusted to be equal to a value of the inlet pressure gauge  8 , the excess leaking stoppage slurry will enter the waste fluid pool  4  through the first back pressure valve  10 , so that the leakage leaking stoppage slurry inside the fluid inlet channel  17  and the inverted corner  18  of the crack simulation mechanism form a dynamic flow; 
     Step Z2, a flow rate of the hydraulic pump  5  is increased to 3 L/min and is kept for 1 h; 
     Step Z3, the flow rate of the hydraulic pump  5  is increased to 4 L/min, and is still kept for 1 h; 
     Step Z4, the flow rate of the hydraulic pump  5  is increased with an increment of 1 L/min per hour until the leakage stoppage layer  200  is damaged; 
     Step Z5, change of the pressure value of the pressure sensor  19  is recoded as an function of time, when it is observed that the pressure value of the pressure sensor  19  changes suddenly, a position of a pressure measurement point on the seam plate  13  that corresponds to the pressure sensor  19  is recorded to determine leaking stoppage location of the leaking stoppage slurry in the crack; and 
     Step Z6, a curve is plotted regarding a relationship between the pressure value of the pressure measuring point on the seam plate  13  and the flow rate. 
     This approach is mainly used to evaluate the effect of hydraulic parameters of the leaking stoppage slurry on stability of the second leaking stoppage layer, wherein the hydraulic parameters include flow rate, displacement, etc. 
     Although the present disclosure has been described in detail with general descriptions and specific embodiments above, it is apparent to those skilled in the art that some modifications or improvements can be implemented on the basis of the present disclosure. Therefore, all these modifications or improvements implemented without departing from the spirit of the present disclosure fall into the scope of the present disclosure. 
     INDUSTRIAL APPLICATION 
     The present disclosure has the following advantages by adopting the foregoing technical solutions: in the dynamic crack leaking stoppage evaluation experiment device and the experiment method thereof disclosed by the present disclosure, when leaking stoppage slurry enters the hollow groove of a rock-mass sample from the fluid inlet channel of the dynamic crack simulation mechanism, the leaking stoppage slurry enters the inverted corners at the top ends of the two seam plates, and the two seam plates are expanded apart from each other to rotate to both sides around the fixed plate, thereby dynamically simulating an aperture-gap cracking process. At the same time, the leaking stoppage slurry enters the crack to plug the crack and form a leaking stoppage layer, as a result which a pressure at entrance of the crack increases, the seam plates would be further expanded apart under the action of the increased pressure, and a second leaking stoppage layer is formed, thereby implementing a dynamic crack leaking stoppage experiment. The dynamic crack leaking stoppage evaluation experiment device disclosed by the present disclosure can simulate a dynamic change process of a crack from a closed sate to an open state, and the experiment method can be applied to study on a variation range of the width of the crack that have been subjected to self-adaptive leaking stoppage with various combinations of leaking stoppage materials and under different increments, and it can also be applied to quantitatively study on effecting patterns of rheological parameters and hydraulic parameters of well drilling fluid on stability of a leaking stoppage layer in the dynamic crack, so that enabled is not only simulation of leaking stoppage process of a dynamic crack, but also real-time monitoring and evaluation on leaking stoppage effect and leaking stoppage location inside the dynamic crack.