CN110361158B - Simulation method and device for stripping and migration of cement reservoir sand in depressurization process - Google Patents
Simulation method and device for stripping and migration of cement reservoir sand in depressurization process Download PDFInfo
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Abstract
The invention discloses a simulation method and a device for sand stripping migration of a hydrate reservoir in a depressurization process, wherein the simulation device comprises a reservoir simulation module, a supply module, a pressure control module, a temperature control module and a recovery module, the reservoir simulation module is used for filling loose sediments, generating a hydrate reservoir and observing a sand stripping starting process, and the reservoir simulation module comprises a microscopic visual module, a pure radial flow reservoir simulation module and a non-radial flow reservoir simulation module; according to the method, the influences of different streamline forms and hydrate distribution rules on the starting and migration processes of the hydrate reservoir sand grains are considered, the hydrate reservoir under the conditions of different hydrate saturation degrees and different hydrate distribution modes is prepared through the reservoir, the hydrate is ensured to be in an undecomposed state in a subsequent sand production mechanism analysis experiment, the sand critical pressure drop condition and the sand production form evolution rule are discussed, and the technical support is provided for the prediction of the sand production rule of the actual exploitation well.
Description
Technical Field
The invention belongs to the field of marine natural gas hydrate development, and particularly relates to a visual simulation method and system for simulating a sand spalling and sand migration microscopic process in a hydrate depressurization exploitation process under different flow field conditions.
Background
With the success of trial production of the sea natural gas hydrate in China for the first time, the evaluation simulation of sand production and influence factors thereof in the sea natural gas hydrate production process quickly becomes a domestic research hotspot. The current focus is mainly to answer the production rule of reservoir sand in the depressurization process by means of numerical simulation or experimental simulation. Due to the lack of field actual sand production test data, experimental simulation becomes a main means for analyzing the sand production mechanism of natural gas hydrate exploitation and predicting the sand production rule. The Qingdao oceanic geology research institute (patent publication No. CN 106950153A; CN106353069A), China oceanic petroleum group Limited company (patent publication No. CN108316913A), China Petroleum university (Huadong) (patent publication No. CN106680435A), China academy of sciences mechanics research institute (patent publication No. CN104950074A) and other units respectively provide a sand production rule simulation experiment system and an experiment method in the hydrate decomposition and production process aiming at different hydrate exploitation working conditions, the key points of the methods are that the rules between the hydrate exploitation, gas production and water production process and the sand production process are considered, and the peeling and migration processes of the sand in a reservoir in the hydrate exploitation process cannot be described from the aspect of micro-mechanism.
Actually, the sand production process in the natural gas hydrate exploitation process is closely related to weakening of the mechanical properties of the reservoir, and the sand production mechanism of the hydrate reservoir is closely related to evolution of the mechanical properties of the reservoir. Therefore, the Qingdao oceanic geological research institute (patent publication No. CN107121359A) considers the coupling relation between the hydrate exploitation sand and the mechanical property, and provides a hydrate sand yield-shear strength combined detection method based on the triaxial mechanical basic test principle. However, the method explains the influence of the sand production process on mechanical properties from a macroscopic view, and has certain help on the peeling mechanism of hydrate reservoir sand grains, but still cannot verify the relationship between the hydrate decomposition process and the sand start migration from a microscopic scale. In order to solve the above problems, patent publication No. CN109254137A attempts to apply X-CT technology to reveal the effect of the sand production process of hydrate reservoirs on the reservoir pores.
The beneficial exploration provides a foundation for the research of the exploitation and sand production process and the sand production mechanism of the hydrate, but the research is mostly carried out under the one-dimensional condition, namely the influence of a reservoir flow field on the reservoir sand stripping and the starting migration process is not considered, and the visual simulation is difficult to realize.
In summary, from the perspective of the simulation research of sand production of natural gas hydrate, the following problems still exist:
(1) at present, the characteristics of heavy rules, light mechanisms, heavy sand production results and the behavior of light sand in a reservoir exist, so that researches on aspects of stripping, starting migration, migration patterns and the like of sand in a stratum need to be enhanced;
(2) although some existing schemes recognize that the reservoir sand production mechanism should be explained from a micro scale, the influence of hydrate decomposition on the sand particle spalling and migration process cannot be discussed from a visualization perspective;
(3) the influence of a special reservoir streamline form on the migration of hydrate reservoir sand grains is not considered, and complex mining modes such as sand grain stripping and starting form description of a special seepage area around a hydraulic slotting gap cannot be met.
Therefore, based on the above problems, it is desirable to provide an indoor simulation method and system capable of discussing the sand stripping, start migration and migration patterns of a hydrate reservoir based on a visualization means, so as to fully consider the influence of the hydrate decomposition rate and the decomposition process on the sand stripping and start migration, and consider different near-well formation seepage laws, thereby providing technical support for exploring the sand production law difference caused by factors such as hydrate decomposition, reservoir flow field and the like.
Disclosure of Invention
The invention provides a simulation method and a simulation system for stripping and migration of sand in a hydrate reservoir in a depressurization process, aims to overcome the defects in the prior art, explores a control mechanism of hydrate reservoir sand production caused by factors such as hydrate decomposition and reservoir flow field by using a visual means, and provides technical support for predicting the sand production rule of an actual production well.
The invention is realized by adopting the following technical scheme:
a simulation method for stripping and migration of cement reservoir sand in a depressurization process comprises the following steps:
(1) selecting a streamline model:
determining a streamline form according to the actual natural gas hydrate reservoir conditions, and selecting a corresponding streamline model, wherein the streamline model comprises a pure radial flow simulation model and a non-radial flow model, and the non-radial flow model comprises a pure linear flow simulation model, a linear gradient pressure drop simulation model, a power function pressure drop gradient simulation model and a negative exponential pressure drop gradient simulation model;
(2) preparing a hydrate simulated reservoir:
installing the streamline model selected in the step (1) into a simulation device for stripping and transferring the cement sand of the hydrate reservoir in the depressurization process, controlling the temperature and pressure conditions, and injecting water and gas into the simulation device to generate hydrate; based on an image segmentation technology, performing threshold segmentation on a sediment section image shot by a microscopic visual module to quantitatively represent the distribution rule of the saturation of the hydrate;
the simulation device for the sand stripping migration of the hydrate reservoir in the depressurization process comprises a reservoir simulation module, a supply module, a pressure control module, a temperature control module and a recovery module, wherein the reservoir simulation module, the supply module, the pressure control module and the recovery module are all arranged in the temperature control module, the supply module, the pressure control module and the recovery module are all connected with the reservoir simulation module, the reservoir simulation module is used for filling loose sediments, generating a hydrate reservoir and observing the starting process of hydrate decomposition and sand stripping, the simulation device comprises a microscopic visual module, a pure radial flow reservoir simulation module and a non-radial flow reservoir simulation module, visual windows are arranged on the pure radial flow reservoir simulation module and the non-radial flow reservoir simulation module, and the microscopic visual module and the visual windows are arranged oppositely;
(3) setting and simulating a pressure reduction process:
controlling the inlet pressure of the reservoir simulation module to be constant, and controlling and adjusting the outlet pressure of the reservoir simulation module to keep the inlet and outlet pressure difference of the reservoir simulation module constant all the time; a supply module is combined to inject a gas-liquid mixture with the same temperature as the internal temperature of the reservoir simulation module, so that the injection rate can maintain the inlet pressure of the model to be stable;
(4) sand start critical depressurization simulation:
changing the pressure difference between the inlet and the outlet of the reservoir simulation module in the step (3), observing the sand grain starting migration conditions at different positions under the fixed hydrate saturation and the fixed hydrate distribution condition, and observing the critical pressure difference of the sand grain starting migration in different hydrate saturation areas by adopting a mode of gradually increasing the pressure difference between the inlet and the outlet of the model so as to establish the relation between the hydrate saturation and the critical pressure drop of the sand grain starting migration;
(5) and (3) sand production type evolution of a hydrate reservoir:
after the silt particle is observed to start to move in the step (4), continuously maintaining constant pressure drop at the inlet and the outlet, and ensuring that the silt particle which starts to move is output and collected; observing the evolution rules of a sand grain migration path and a migration channel in real time based on a microscopic visual module to determine the formation sand production state under the conditions of constant production pressure drop and certain hydrate saturation distribution;
(6) controlling the sand production of the hydrate reservoir by the streamline form:
and (5) after the steps (1) to (5) are completed, replacing the streamline model, repeating the steps (2) to (5), and verifying the mesoscopic sand mechanism of the hydrate reservoir under the limited condition of other streamline models.
Further, in the step (3), in the setting and simulation process of the depressurization flow, it is ensured that absolute pressure values of an outlet and an inlet of the reservoir simulation module are both higher than the hydrate phase equilibrium pressure, and it is ensured that the formed hydrate is in an undecomposed state.
The invention also provides a simulation device for the sand stripping and migration of the hydrate reservoir in the depressurization process, which comprises a reservoir simulation module, a supply module, a pressure control module, a temperature control module and a recovery module, wherein the reservoir simulation module, the supply module, the pressure control module and the recovery module are all arranged in the temperature control module;
the reservoir simulation module is used for filling loose sediments, generating a hydrate reservoir and observing the starting processes of hydrate decomposition and sand spallation, and comprises a microscopic visual module, a pure radial flow reservoir simulation module and a non-radial flow reservoir simulation module, wherein visual windows are arranged on the pure radial flow reservoir simulation module and the non-radial flow reservoir simulation module, and the microscopic visual module and the visual windows are arranged oppositely; a pure radial flow simulation model is arranged in the pure radial flow reservoir simulation module, and a pure linear flow simulation model, a linear gradient pressure drop simulation model, a power function pressure drop gradient simulation model or a negative exponential pressure drop gradient simulation model is arranged in the non-radial flow reservoir simulation module.
Further, the reservoir simulation module comprises an upper valve shell, a lower valve shell, a visual window, a mixed fluid inlet, a mixed fluid outlet, a reservoir sediment filling groove, a confining pressure cavity, an inlet diversion groove and an outlet diversion groove, wherein the inlet diversion groove is arranged at the mixed fluid inlet end, and the outlet diversion groove is arranged at the mixed fluid outlet end; the upper valve shell and the lower valve shell are connected through fastening bolts, and the visual window is arranged in the center of the upper valve shell; the lower valve shell is provided with a groove with the same diameter as the visual window on the upper valve shell, the reservoir sediment filling groove is arranged in the groove and matched with the groove, different streamline models are arranged in the reservoir sediment filling groove, and the structure of the reservoir sediment filling groove is matched with the structure of the streamline models.
Further, for the non-radial flow reservoir simulation module, the streamline model arranged in the reservoir sediment filling groove comprises: the device comprises a pure linear flow simulation model, a linear gradient pressure drop model, a power function pressure drop gradient model and a negative exponential pressure drop gradient model, wherein a mixed fluid inlet and a mixed fluid outlet are oppositely arranged on the side surface of a reservoir simulation module.
Further, for the pure radial flow reservoir stratum simulation module, the pure radial flow reservoir stratum sediment filling groove is integrally disc-shaped, the pure radial flow inlet diversion groove is arranged along the outer edge of the pure radial flow reservoir stratum sediment filling groove, and the mixed fluid outlet is positioned in the center of the lower valve shell.
Furthermore, pressure-resistant glass is arranged above the inlet diversion trench and the outlet flow collecting trench, the outer edge of the pressure-resistant glass is sealed with the upper valve shell through a sliding sealing ring, a confining pressure cavity is arranged above the pressure-resistant glass and is connected with a confining pressure inlet and outlet on the side wall of the upper valve shell, and the upper part of the confining pressure cavity is fixedly matched with the upper valve shell through a visual window.
Further, the supply module comprises a gas supply module, a liquid supply module and a gas-liquid mixing module, the gas supply module and the liquid supply module are connected with the inlet end of the gas-liquid mixing module, and the outlet end of the gas-liquid mixing module is connected with the reservoir simulation module.
Furthermore, the recovery module comprises a first control recovery system and a second control recovery system, the first control recovery system is connected with an outlet of the non-radial flow reservoir simulation module, and the second control recovery system is connected with an outlet of the pure radial flow reservoir simulation module.
Furthermore, the pressure control module comprises an inlet pressure control pump, a first outlet pressure control pump and a second outlet pressure control pump, the first outlet pressure control pump is connected with the first control recovery system, and the second outlet pressure control pump is connected with the second control recovery system.
Compared with the prior art, the invention has the advantages and positive effects that:
(1) considering the influence of different streamline forms on the starting and migration processes of hydrate reservoir sand grains, designing a corresponding reservoir simulation module structure and a corresponding simulation method process, and directly providing support for the design of the reservoir modification leading edge form by research results;
(2) by controlling different hydrate saturation degrees and different hydrate distribution modes in the reservoir preparation process, the hydrate is ensured to be in a stable state in a subsequent sand production mechanism analysis experiment, and the influence of the hydrate decomposition process on the sand production mechanism analysis result is eliminated, so that the sand production pattern and the evolution thereof of the reservoir can be more accurately reflected;
(3) when the hydrate reservoir is prepared, a microscopic image segmentation technology is utilized, the method is applied to the partitioning of the migration pattern of hydrate reservoir sand grains and the distribution of hydrate saturation, and the visual simulation of hydrate sand grain microscopic starting migration is realized;
according to the scheme, the influences of the hydrate decomposition rate and the stripping and the starting migration of the sediment in the decomposition process are fully considered, different near-well stratum seepage rules are considered, and technical support is provided for exploring the difference of sand production rules caused by factors such as hydrate decomposition and reservoir flow field.
Drawings
FIG. 1 is a schematic view of a simulation apparatus for a mesoscopic process of the flaking and migration of hydrate sand and sand in example 1 of the present invention;
FIG. 2 is a schematic cross-sectional structural diagram of a pure radial flow reservoir simulation module according to example 1 of the present invention;
FIG. 3 is a schematic diagram of different etching structures inside a sediment filling tank according to embodiment 1 of the present invention;
FIG. 4 is a schematic flow chart of a simulation method of the silt peeling and migration microscopic process according to embodiment 2 of the present invention;
wherein: 1. a gas supply module; 2. a liquid supply module; 3. a gas-liquid mixing module; 4. an inlet pressure control pump; 5. a microscopic visualization module; 6-1, a non-radial inflow inlet guide groove; 6-2, a pure radial inflow inlet guide groove; 7-1, filling a non-radial flow reservoir sediment filling groove; 7-1-1, pure linear flow simulation model; 7-1-2, a linear gradient pressure drop flow simulation model; 7-1-3, power function pressure drop gradient simulation model; 7-1-4, a negative exponential pressure drop gradient simulation model; 7-2, filling a pure radial flow reservoir sediment filling groove; 8-1, a non-radial outflow port collecting groove; 8-2, a pure radial outflow port collecting groove; 9-1, a non-radial flow reservoir simulation module; 9-2, a pure radial flow reservoir simulation module; 9-2-1, an upper petal shell; 9-2-2, lower valve shell; 9-2-3, a mixed fluid inlet; 9-2-4, a confining pressure inlet and outlet; 9-2-5, sealing between the reservoir simulation module body and the confining pressure isolation layer; 9-2-6, a visual window; 9-2-7, enclosing a pressure cavity; 9-2-8 parts of pressure-resistant glass; 9-2-9, fastening bolts; 9-2-10, a mixed fluid outlet; 10-1, a first control recovery system; 10-2, a second control recovery system; 11-1, a first outlet pressure control pump; 11-2, a second outlet pressure control pump; 12-1, a first confining pressure control pump; 12-2, a second confining pressure control pump; 13. a temperature control module; F1-F19 and a valve.
Detailed Description
In order that the above objects and advantages of the present invention may be more clearly understood, particular embodiments of the invention will be described in detail below with reference to the accompanying drawings:
embodiment 1, a simulation apparatus for stripping and transporting hydrate reservoir sands in a depressurization process, taking a hydrate depressurization production process as an example, as shown in fig. 1, the simulation apparatus includes a reservoir simulation module (9-1,9-2), a supply module (1,2,3), a pressure control module (4,11-1,11-2,12-1,12-2), a temperature control module 13, and a recovery module (10-1,10-2), the reservoir simulation module (9-1,9-2), the supply module (1,2,3), the pressure control module (4,11-1,11-2,12-1,12-2), and the recovery module (10-1,10-2) are all disposed in the temperature control module 13, the temperature control module 13 is mainly used for cooling the simulation apparatus, maintaining temperature conditions required for hydrate reservoir simulation;
with continuing reference to fig. 1, the reservoir simulation module is used for filling loose sediments, generating a hydrate reservoir and observing the starting process of hydrate decomposition and sand spallation, and is a core module of the system, and comprises a microscopic visual module 5, a pure radial flow reservoir simulation module 9-2 and a non-radial flow reservoir simulation module 9-1, wherein visual windows are arranged on the pure radial flow reservoir simulation module 9-2 and the non-radial flow reservoir simulation module 9-1, and the microscopic visual module 5 is arranged opposite to the visual windows;
the supply module comprises a gas supply module 1, a liquid supply module 2 and a gas-liquid mixing module 3, the gas supply module 1 and the liquid supply module 2 are connected with the inlet end of the gas-liquid mixing module 3, and the outlet end of the gas-liquid mixing module 3 is connected with the reservoir simulation module and used for supplying high-pressure gas and water to the reservoir simulation module;
the recovery module is mainly used for recovering gas-liquid solids produced by the reservoir simulation module and comprises a first control recovery system 10-1 and a second control recovery system 10-2, the first control recovery system 10-1 is connected with an outlet of the non-radial flow reservoir simulation module 9-1, and the second control recovery system 10-2 is connected with an outlet of the pure radial flow reservoir simulation module 9-2;
the pressure control module comprises an inlet pressure control pump 4, a first outlet pressure control pump 11-1, a second outlet pressure control pump 11-2, a first confining pressure control pump 12-1 and a second confining pressure control pump 12-2, wherein the first outlet pressure control pump 11-1 is connected with a first control recovery system 10-1, the second outlet pressure control pump 11-2 is connected with a second control recovery system 10-2, and the pressure control module is mainly used for controlling the inlet pressure, the outlet pressure and the system pressure of the reservoir simulation module. The first confining pressure control pump 12-1 and the second confining pressure control pump 12-2 are respectively connected with confining pressure cavity outlets on the non-radial flow reservoir simulation module 9-1 and the pure radial flow reservoir simulation module 9-2, and control the confining pressure of sediment filled in the reservoir simulation module.
The reservoir simulation module in the embodiment comprises an upper valve shell, a lower valve shell, a visual window, a mixed fluid inlet, a mixed fluid outlet, a reservoir sediment filling groove, a confining pressure cavity, an inlet diversion trench, an outlet diversion trench and the like; the upper valve shell and the lower valve shell are connected through fastening bolts, the visual window is arranged in the center of the upper valve shell, and the window of the visual window can cover the range of all reservoir sediment filling grooves; the lower valve shell is provided with a groove with the same diameter as the visual window on the upper valve shell, the reservoir sediment filling groove is positioned in the groove, the outer edge of the reservoir sediment filling groove is matched with the lower valve shell groove, a streamline model arranged in the reservoir sediment filling groove is designed according to different simulated streamline types, the streamline model is a sediment filling groove with different shapes formed based on the technologies such as 3D printing and the like, is an existing mature technology, the outer edge of the streamline model is consistent with the inner wall of the filling groove, and the inner edge of the streamline model is designed according to the streamline form to be simulated, and mainly comprises a pure linear flow simulation model 7-1-1, a linear gradient pressure drop flow simulation model 7-1-2, a power function pressure drop gradient simulation model 7-1-3, a negative exponential pressure drop gradient simulation model 7-1-4 and the like.
The four streamline models are for a non-radial flow reservoir simulation module 9-1, a mixed fluid inlet and a mixed fluid outlet are oppositely arranged on the side surface of the reservoir simulation module, the shape of the inner edge of a corresponding reservoir sediment filling groove corresponds to the outer edge of the streamline model, for a pure linear flow simulation model 7-1-1, the length of an injection end splitter box is the same as that of an outflow end splitter box, the outline of the inner edge of the filling box is of a standard rectangular structure, and for a linear gradient pressure drop model 7-1-2, the distance between the boundaries of the two sides of the inner edge of the model is linearly reduced from the injection end splitter box to the outflow end splitter box; similarly, for the power function pressure drop gradient model 7-1-3 and the negative exponent pressure drop gradient model 7-1-4, it is assumed that the flow pressure drop around the wellbore or around the modified fracture of the modified formation conforms to the power function form and the negative exponent form, the inner edge side boundary of the power function pressure drop gradient model is the power function, and the inner edge side boundary of the negative exponent pressure drop gradient model is the exponent function.
In the streamline model with different streamline forms, the diversion trench is arranged at the mixed fluid inlet end to ensure that the fluid uniformly enters the sediment section, the diversion trench is communicated with the mixed fluid inlet of the reservoir simulation module, the flow collecting trench is arranged at the mixed fluid outlet end, and the flow collecting trench is communicated with the mixed fluid outlet end of the reservoir simulation module.
For the pure radial flow reservoir simulation module, the structure is similar to that of a non-radial flow reservoir simulation module, and as shown in FIG. 2, the pure radial flow reservoir simulation module comprises an upper valve shell 9-2-1, a lower valve shell 9-2-2, a visible window 9-2-6, a mixed fluid inlet 9-2-3, a mixed fluid outlet 9-2-10, a pure radial flow reservoir sediment filling groove 7-2, a confining pressure cavity 9-2-7, a pure radial flow inlet diversion groove 6-2 and a pure radial flow outlet diversion groove 8-2; the upper valve shell 9-2-1 and the lower valve shell 9-2-2 are connected through a fastening bolt 9-2-9, and the visual window 9-2-6 is arranged in the center of the upper valve shell 9-2-1; the lower valve shell 9-2-2 is provided with a groove with the same diameter as the visual window on the upper valve shell 9-2-1, the pure radial flow reservoir sediment filling groove 7-2 is positioned in the groove, and the outer edge of the pure radial flow reservoir sediment filling groove 7-2 is matched with the groove of the lower valve shell. The difference from the non-radial flow reservoir simulation module 9-1 is that: the integral of a sediment filling groove designed in the sediment filling groove is in a disc shape, an inlet diversion groove 6-2 is arranged along the outer circumference of the disc shape, and a mixed fluid outlet 9-2-10 is positioned at the central position of a lower valve shell, so that the design mainly considers that the positions of an inlet and an outlet of a pure radial flow model and the pure linear flow simulation model, the linear gradient pressure drop model, the power function pressure drop gradient model and the negative exponent pressure drop gradient model are different, and cannot be mutually installed with the pure linear flow simulation model, the linear gradient pressure drop model, the power function pressure drop gradient model or the negative exponent pressure drop gradient model, so that two reservoir simulation modules are slightly modified.
In addition, pressure-resistant glass 9-2-8 is further installed above the sediment filling model, the flow guide groove and the flow collecting groove in different streamline forms, the outer edge of the pressure-resistant glass 9-2-8 is sealed with a shoulder on the upper valve shell through a sliding sealing ring 9-2-5, a confining pressure cavity 9-2-7 is arranged above the pressure-resistant glass, and the confining pressure cavity 9-2-7 is connected with a confining pressure inlet and outlet 9-2-4 in the side wall of the upper valve shell; the upper part of the confining pressure cavity 9-2-7 is fixedly matched with the upper valve shell body and is provided with a transparent visual window 9-2-6.
Example 2, when implemented, the following basic principles are considered:
(1) under the condition of the same stratum seepage rate, the change of the microscopic stress balance condition of the particles can be caused by the difference of the convergence degree of the streamline. Thus, the amount of sand production from the near-well formation is affected by the flow field around the wellbore or fracture at the same outlet flow rate (production). Therefore, by controlling the flow boundary of the model, simulation of the sand start migration process under different streamline conditions can be realized;
(2) the saturation difference of the hydrate influences the cementation degree of the sand particles at different positions, and the uneven distribution of the hydrate in a reservoir stratum is one of the main factors for controlling the unevenness of sand production positions in the stratum. Under the condition of the same flow velocity (production pressure difference), the sand grain starting migration critical flow velocities at different positions are different, and the relation between the sequence of the sand grain starting migration positions and the hydrate distribution in a hydrate reservoir can be observed by using a microscope system, so that the influence of the hydrate saturation on the sand grain starting migration critical flow velocity of the reservoir can be defined;
(3) hydrate saturation distribution may be a major factor affecting hydrate reservoir sand patterns (pore liquefaction, wormhole, continuous collapse). And observing the hydrate saturation distribution, the sand grain migration path under a certain flow rate condition and the migration rate in a visual field range through a high-power microscope to obtain the microcosmic coupling relation between the hydrate distribution and the sand production form.
Based on the above basic test principle, corresponding to the visual simulation apparatus for mud stripping and migration mesoscopic process in the hydrate depressurization mining process described in embodiment 1, this embodiment provides a visual simulation method for mud stripping and migration mesoscopic process in the hydrate depressurization mining process, as shown in fig. 4, including:
(1) selecting a streamline model: selecting a pure linear flow simulation model, a linear gradient pressure drop simulation model, a power function pressure drop gradient simulation model, a negative exponential pressure drop gradient simulation model or a pure radial flow simulation model according to the flowing form around the well or the fracture possibly occurring in the actual natural gas hydrate exploitation well, filling actual sediments in the corresponding streamline model, and installing an instrument;
(2) preparing a hydrate simulated reservoir: installing simulation models with different streamline forms into the simulation device for stripping and transferring the cement sand of the hydrate reservoir in the depressurization process, controlling the temperature and pressure conditions and injecting water gas into the simulation device to generate hydrate; based on an image segmentation technology, performing threshold segmentation on a sediment section image shot by a microscopic visual module, and quantitatively representing the distribution rule of the hydrate saturation;
(3) and (3) pressure reduction process simulation: controlling the inlet pressure of the reservoir simulation module to be constant, and controlling and adjusting the outlet pressure of the reservoir simulation module to keep the pressure difference between the inlet and the outlet of the reservoir simulation module constant all the time; a supply module is combined, and a gas-liquid mixture with the same internal temperature as the reservoir simulation module is injected into the reservoir simulation module; the injection rate is based on the fact that the pressure at the inlet of the model can be maintained to be stable;
it should be noted that, in step (3), it is necessary to ensure that the hydrate formed is in an undecomposed state, and since the main purpose of the sand stripping and migration process described in this embodiment is to explore the influence of the flow pattern and hydrate saturation distribution of the hydrate reservoir on the sand stripping and migration initiation and sand production pattern, so as to explore the micro-scale sand production mechanism of the hydrate reservoir. If the hydrate is in a dynamic decomposition state in the sand grain starting migration process, the fact that the starting migration of the sand grains is caused by the hydrate decomposition or the hydrate distribution and streamline influence cannot be verified, only the hydrate reservoir sand production rule can be finally obtained, and the explanation of the hydrate sand production mechanism cannot be completely explained.
(4) Sand start critical pressure drop simulation: changing the pressure difference between the inlet and the outlet of the model in the step (3), observing the sand grain starting migration conditions at different positions under the fixed hydrate saturation and hydrate distribution conditions, and observing the critical pressure difference of sand grain starting migration in different hydrate saturation areas by adopting a mode of gradually increasing the pressure of the inlet and the outlet of the model in a stepped mode so as to establish the relationship between the hydrate saturation and the critical pressure drop of sand grain starting migration; (5) and (3) sand production type evolution of a hydrate reservoir: after the silt particle is observed to start to move in the step (4), continuously maintaining constant pressure drop at the inlet and the outlet, and ensuring that the silt particle which starts to move is output and collected; observing the evolution rules of a sand grain migration path and a migration channel in real time based on a microscopic visual module, thereby determining the formation sand production state under the conditions of constant production pressure drop and certain hydrate saturation distribution;
it is particularly emphasized that the absolute value of the outlet pressure of the model is always kept larger than the phase equilibrium pressure of the hydrate in the simulation process of the step (4) so as to eliminate the influence of the weakening of the sediment cementation caused by the decomposition of the hydrate on the starting migration process of the sand grains. Therefore, the present embodiment realizes the simulation of the sand start critical "pressure drop" and the evolution of the sand production pattern by controlling the pressure difference at the inlet and the outlet. This is consistent with the reality of an actual natural gas hydrate producing reservoir: in the actual natural gas hydrate exploitation process, the main factor influencing the formation sand production condition is also due to the pressure difference formed by the formation pressure and the wellbore pressure, and is not the absolute pressure value of the formation.
(6) Controlling the sand production of the hydrate reservoir by the streamline form: and (5) after the steps (1) to (5) are completed, replacing the streamline simulation model, repeating the steps (2) to (5), and verifying the mesoscopic sand mechanism of the hydrate reservoir under other streamline limit conditions.
In a word, the visual simulation device and method for the mud sand stripping and migration process in the hydrate depressurization exploitation process, which are provided by the scheme of the invention, can observe the influence of different streamline forms on the sand start and migration processes, and realize the visual observation of the sand production forms of hydrate reservoirs under different hydrate saturation degrees and distribution conditions and the evolution rules of the sand production forms; the influence of the hydrate saturation and the distribution thereof on the critical flow velocity condition of silt sand starting migration is effectively simulated and evaluated, so that the control mechanism of hydrate reservoir sand production caused by factors such as hydrate decomposition, reservoir flow field and the like is explored by a visual means, and technical support is provided for the prediction of the sand production rule of an actual production well.
The above description is only a preferred embodiment of the present invention, and not intended to limit the present invention in other forms, and any person skilled in the art may apply the above modifications or changes to the equivalent embodiments with equivalent changes, without departing from the technical spirit of the present invention, and any simple modification, equivalent change and change made to the above embodiments according to the technical spirit of the present invention still belong to the protection scope of the technical spirit of the present invention.
Claims (9)
1. The simulation method for the sand stripping migration of the hydrate reservoir during the depressurization process is characterized by comprising the following steps of:
(1) selecting a streamline model:
determining a streamline form according to the actual natural gas hydrate reservoir conditions, and selecting a corresponding streamline model, wherein the streamline model comprises a pure radial flow simulation model and a non-radial flow model, and the non-radial flow model comprises a pure linear flow simulation model, a linear gradient pressure drop simulation model, a power function pressure drop gradient simulation model and a negative exponential pressure drop gradient simulation model;
(2) preparing a hydrate simulated reservoir:
installing the streamline model selected in the step (1) into a simulation device for stripping and transferring the cement sand of the hydrate reservoir in the depressurization process, controlling the temperature and pressure conditions, and injecting water and gas into the simulation device to generate hydrate; based on an image segmentation technology, performing threshold segmentation on a sediment section image shot by a microscopic visual module to quantitatively represent the distribution rule of the saturation of the hydrate;
the simulation device for the sand stripping migration of the hydrate reservoir in the depressurization process comprises a reservoir simulation module, a supply module, a pressure control module, a temperature control module and a recovery module, wherein the reservoir simulation module, the supply module, the pressure control module and the recovery module are all arranged in the temperature control module, the supply module, the pressure control module and the recovery module are all connected with the reservoir simulation module, the reservoir simulation module is used for filling loose sediments, generating a hydrate reservoir and observing the starting process of hydrate decomposition and sand stripping, the simulation device comprises a microscopic visual module, a pure radial flow reservoir simulation module and a non-radial flow reservoir simulation module, visual windows are arranged on the pure radial flow reservoir simulation module and the non-radial flow reservoir simulation module, and the microscopic visual module and the visual windows are arranged oppositely;
(3) setting and simulating a pressure reduction process:
controlling the inlet pressure of the reservoir simulation module to be constant, and controlling and adjusting the outlet pressure of the reservoir simulation module to keep the inlet and outlet pressure difference of the reservoir simulation module constant all the time; a supply module is combined to inject a gas-liquid mixture with the same temperature as the internal temperature of the reservoir simulation module, so that the injection rate can maintain the inlet pressure of the model to be stable;
(4) sand start critical depressurization simulation:
changing the pressure difference between the inlet and the outlet of the reservoir simulation module in the step (3), observing the sand grain starting migration conditions at different positions under the fixed hydrate saturation and the fixed hydrate distribution condition, and observing the critical pressure difference of the sand grain starting migration in different hydrate saturation areas by adopting a mode of gradually increasing the pressure difference between the inlet and the outlet of the model so as to establish the relation between the hydrate saturation and the critical pressure drop of the sand grain starting migration;
(5) and (3) sand production type evolution of a hydrate reservoir:
after the silt particle is observed to start to move in the step (4), continuously maintaining constant pressure drop at the inlet and the outlet, and ensuring that the silt particle which starts to move is output and collected; observing the evolution rules of a sand grain migration path and a migration channel in real time based on a microscopic visual module to determine the formation sand production state under the conditions of constant production pressure drop and certain hydrate saturation distribution;
(6) controlling the sand production of the hydrate reservoir by the streamline form:
and (5) after the steps (1) to (5) are completed, replacing the streamline model, repeating the steps (2) to (5), and verifying the mesoscopic sand mechanism of the hydrate reservoir under the limited condition of other streamline models.
2. The simulation method of the sand stripping migration of the hydrate reservoir in the depressurization process according to claim 1, wherein: in the step (3), in the setting and simulation process of the depressurization flow, the absolute pressure values of the outlet and the inlet of the reservoir simulation module are both higher than the phase equilibrium pressure of the hydrate, and the formed hydrate is ensured to be in an undecomposed state.
3. The utility model provides a simulation device that hydrate reservoir silt sand stripped and moved in depressurization process which characterized in that: the device comprises a reservoir simulation module, a supply module, a pressure control module, a temperature control module and a recovery module, wherein the reservoir simulation module, the supply module, the pressure control module and the recovery module are all arranged in the temperature control module, the temperature control module is used for maintaining the temperature condition required by hydrate reservoir simulation, the supply module is used for supplying high-pressure gas and water to the reservoir simulation module, the pressure control module is used for controlling the inlet pressure, the outlet pressure and the system pressure of the reservoir simulation module, and the recovery module is used for recovering gas-liquid solids produced by the reservoir simulation module;
the reservoir simulation module is used for filling loose sediments, generating a hydrate reservoir and observing the starting processes of hydrate decomposition and sand spallation, and comprises a microscopic visual module, a pure radial flow reservoir simulation module and a non-radial flow reservoir simulation module, wherein visual windows are arranged on the pure radial flow reservoir simulation module and the non-radial flow reservoir simulation module, and the microscopic visual module and the visual windows are arranged oppositely; a pure radial flow simulation model is arranged in the pure radial flow reservoir simulation module, and a pure linear flow simulation model, a linear gradient pressure drop simulation model, a power function pressure drop gradient simulation model or a negative exponential pressure drop gradient simulation model is arranged in the non-radial flow reservoir simulation module;
the reservoir simulation module comprises an upper valve shell, a lower valve shell, a visual window, a mixed fluid inlet, a mixed fluid outlet, a reservoir sediment filling groove, a confining pressure cavity, an inlet diversion groove and an outlet flow collection groove, wherein the inlet diversion groove is arranged at the mixed fluid inlet end, and the outlet flow collection groove is arranged at the mixed fluid outlet end; the upper valve shell and the lower valve shell are connected through fastening bolts, and the visual window is arranged in the center of the upper valve shell; the lower valve shell is provided with a groove with the same diameter as the visual window on the upper valve shell, the reservoir sediment filling groove is arranged in the groove and matched with the groove, different streamline models are arranged in the reservoir sediment filling groove, and the structure of the reservoir sediment filling groove is matched with the structure of the streamline models.
4. The simulation device for stripping and migration of cement reservoir sands in the depressurization process according to claim 3, wherein: for the non-radial flow reservoir simulation module, a pure linear flow simulation model, a linear gradient pressure drop model, a power function pressure drop gradient model or a negative exponential pressure drop gradient model are arranged in a reservoir deposit filling groove, and a mixed fluid inlet and a mixed fluid outlet are oppositely arranged on the side face of the reservoir simulation module.
5. The simulation device for stripping and migration of cement reservoir sands in the depressurization process according to claim 3, wherein: for the pure radial flow reservoir stratum simulation module, the pure radial flow reservoir stratum sediment filling groove is integrally disc-shaped, the pure radial flow inflow guide groove is arranged along the outer edge of the pure radial flow reservoir stratum sediment filling groove, and the mixed fluid outlet is positioned in the center of the lower valve shell.
6. The simulation device for stripping and migration of cement reservoir sands in the depressurization process according to claim 4 or 5, wherein: pressure-resistant glass is arranged above the inlet diversion trench and the outlet flow collecting trench, the outer edge of the pressure-resistant glass is sealed with the upper valve shell through a sliding seal ring, a confining pressure cavity is arranged above the pressure-resistant glass, the confining pressure cavity is connected with a confining pressure inlet and outlet on the side wall of the upper valve shell, and the upper part of the confining pressure cavity is fixedly matched with the upper valve shell through a visual window.
7. The simulation device for stripping and migration of cement reservoir sands in the depressurization process according to claim 3, wherein: the supply module comprises a gas supply module, a liquid supply module and a gas-liquid mixing module, the gas supply module and the liquid supply module are connected with the inlet end of the gas-liquid mixing module, and the outlet end of the gas-liquid mixing module is connected with the reservoir simulation module.
8. The simulation device for stripping and migration of cement reservoir sands in the depressurization process according to claim 3, wherein: the recovery module comprises a first control recovery system and a second control recovery system, the first control recovery system is connected with an outlet of the non-radial flow reservoir simulation module, and the second control recovery system is connected with an outlet of the pure radial flow reservoir simulation module.
9. The simulation device for stripping and migration of cement reservoir sands in the depressurization process according to claim 3, wherein: the pressure control module comprises an inlet pressure control pump, a first outlet pressure control pump and a second outlet pressure control pump, the first outlet pressure control pump is connected with the first control recovery system, and the second outlet pressure control pump is connected with the second control recovery system.
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| CN111691881B (en) * | 2020-07-03 | 2023-12-22 | 中国石油大学(北京) | Device and method for simulating thermal settlement of hydrate-containing stratum |
| CN112014293A (en) * | 2020-09-07 | 2020-12-01 | 中国石油大学(华东) | Method and device for representing hydrate reservoir seepage capability |
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| CN112630407A (en) * | 2020-12-09 | 2021-04-09 | 同济大学 | Microcosmic visual simulation experiment device and method for seepage and sand production of hydrate reservoir |
| CN114961661A (en) * | 2021-02-19 | 2022-08-30 | 中国石油天然气集团有限公司 | Sea natural gas hydrate exploitation reservoir sand migration experimental device and experimental method |
| CN114059974A (en) * | 2021-11-17 | 2022-02-18 | 北京大学 | Sand prevention method, device and experimental method for sea area hydrate reservoir radial well composite liquid-solid phase change material |
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