Physical Simulation Experiments Research Articles

A Multicomponent Thermal Fluid Numerical Simulation Method considering Formation Damage

Multicomponent thermal fluid huff and puff is an innovative heavy oil development technology for heavy oil reservoirs, which has been widely used in offshore oilfields in China and has proved to be a promising method for enhancing oil recovery. Components of multicomponent thermal fluids contain many components, including carbon dioxide, nitrogen, and steam. Under high temperature and high pressure conditions, the complex physical and chemical reactions between multicomponent thermal fluids and reservoir rocks occur, which damage the pore structure and permeability of core. In this paper, the authors set up a reservoir damage experimental device, tested the formation permeability before and after the injection of multiple-component thermal fluids, and obtained the formation damage model. The multicomponent thermal fluid formation damage model is embedded in the component control equation, the finite difference method is used to discretize the control equation, and a new multielement thermal fluid numerical simulator is established. The physical simulation experiment of multicomponent thermal fluid huff and puff is carried out by using the actual sand-packed model. By comparing the experimental results with the numerical simulation results, it is proved that the new numerical simulation model considering formation damage proposed in this paper is accurate and reliable.

Microscope dynamic characterization of oil charging in tight sandstone using a physical simulation experiment

Physical processes of oil charging in tight sandstone were simulated and analyzed using oil displacement water in sandstone micro-visualization models. Microscope dynamic characterizations of oil charging were obtained, and factors controlling the oil charging process in tight sandstones were elucidated in combination with thin section analysis, scanning electron microscopy (SEM) and rate-controlled porosimetry (RCP). Results indicate that three types of residual water exist in tight sandstone reservoirs: water-in-oil droplets; corner residual water; and connect-pore residual water. The charging rate of oil varied in the direction of migration, and uniform oil-water interfaces were not recorded during oil charging. The dynamic process of oil charging was classified as: (i) fingerlike and (ii) netlike. During fingerlike oil charging processes, the frontal movement formed obvious dominant paths, and the residual water area was large. During netlike oil charging processes, oil migrated through multiple channels forming a network of paths, having high terminal oil saturation. Due to the narrow pore-throat, oil charging characteristics of tight sandstones are not sensitive to variations of pore-throat radii; charging characteristics depend on the effective storage space and connectivity of the pore-throat. Connectivity of the dissolution pore-throat was found to be good, and the effective storage space of dissolution combined pores was large. Our results, therefore, indicate that oil charging of tight sandstone is controlled by pore-throat structures formed by dissolution.

Formation conditions and evolution of fractures in multiple tight rocks: Implications for unconventional reservoir exploitation

Physical simulation experiments of rock fracturing can effectively simulate the extension of artificial fractures within different lithology and interbedded rocks. Previous studies have focused on the conditions of artificial fracture initiation and propagation, while few studies have been conducted on the evolution and influencing factors of fractures in reservoir rocks. In this study, fracture evolution simulation was performed using a self-developed physical fracturing simulation device and a real-time acoustic emission fracture monitoring system. Results show the presence of four main fracture patterns within the selected lithologies and their combinations, including simple shear, simple, network, and X-shear fracture patterns. The variation trend of the principal stress difference and fracture pressure, as well as the values of the network, X-shear, simple, and simple shear fracture patterns all increased successively. The values of the network and X-shear fracture patterns were smallest, while the fracture pressure and principal stress difference were less than 65 and 40 MPa, respectively. Furthermore, the trends of the brittle mineral content and brittleness index were opposite.The interlaminar modulus difference mainly controls the cracks extending at the interface of the interlayer, and is conducive to the extension of cracks at values less than 3 GPa. Furthermore, the tendency of network, X-shear, simple, and simple shear fracture patterns to gradually simplify implies that the fracturing treatment effect and fracturing performance may have sequentially deteriorated. This study may provide a reference for the determination of reservoir fracturing ability and fracturing reconstruction design in unconventional reservoir development.

Structural Characteristics Analysis of Overlying Rocks and Prevention Measures with a Long‐Wall Face Passing Across Abandoned Roadways: A Case Study

In order to study the occurrence mechanism of advanced coal pillar instability failure and support crushing accidents during a long‐wall face passing across abandoned roadways period, the Panel LW3101 in Shenghua Colliery was taken as a typical engineering background. By means of in situ investigation, physical simulation experiment, theoretical analysis, in situ tests, and relevant monitoring methods, the occurrence mechanism and prevention measures are studied. The results show that the bearing stress in advanced coal pillar is accumulated larger and larger with the width of advanced coal pillar gradually decreasing, and meanwhile, the key stratum in overlying strata would also be sliding instability under some minimum critical width condition; the sudden failure of advanced coal pillar which leads to a sharp increase of bending moment is the key factor that induces fracture of the main roof in front of long‐wall face, and the advanced fracture of the main roof can be prevented by changing the stress state of the advanced coal pillar from a two‐dimensional state to a three‐dimensional state; the method of backfilling abandoned roadway is used to improve the stability of advanced coal pillar and the corresponding monitoring results verify that this method is effective. The research conclusions provide a theoretical foundation and new guidance for preventing advanced coal pillar instability failure and support crushing accidents under a long‐wall face passing across abandoned roadways condition.

Boundary distribution of top-coal limit-equilibrium zone in fully mechanized caving in steeply dipping coal seams

In fully mechanized caving mining, the earlier the top coal enters the limit-equilibrium zone, the easier it is for leakage to be induced in front of the support. As the dip angle of the seam increases, the leakage of the top coal in front of the support drastically reduces the stability of the stope support–surrounding rock system. In this study, theoretical analysis, a physical simulation experiment, a numerical simulation, and field measurements were performed to consider the influence of the coal seam dip effect on the gradual deterioration of top coal for the first time, and quantitative characterization of the limit equilibrium boundary of top coal was realized based on analysis of the continuous damage medium mechanics. The results show that the two boundaries exhibit a consistent, asymmetric ‘double arch’ distribution along the incline. The top coal in the inclined upper-middle region of the working face is the first to enter the limit-equilibrium state, whereas the inclined upper and lower regions lag behind. The initial and final boundaries of the limit-equilibrium zone are distributed from 1.24 to 3.04 m and from 0.19 to −1.95 m in front of the coal wall, respectively. The distribution of the limit-equilibrium zone boundary was verified by the leakage times of the top coal in the working face. These results could provide reference information for evaluating stope support–surrounding rock systems in fully mechanized caving mining with steeply dipping coal seams.

The Influence of Interlayer on the Expansion of Steam Chamber of Oil Sand SAGD Development

The steam-assisted gravity drainage (SAGD) technology is currently a more effective frontier technology for the exploitation of heavy oil, and it has a better development effect than other exploitation methods. The formation and expansion of the steam chamber is the key to SAGD technology, and the interlayer is an important influencing factor. Therefore, it is of great significance to study the influence of the interlayer on the expansion of the steam chamber and the effect of SAGD development during the oil sand SAGD development process. In order to study the influence of the interlayer on the expansion of the steam chamber during the oil sand SAGD development process, a double-horizontal well SAGD physical experiment simulation experiment was carried out using the experimental device of the thermal recovery physical simulation system. The influence of interlayer on the expansion law of the steam chamber during the SAGD development of dual horizontal wells is studied. Studies have shown that the interlayer inhibits the longitudinal development of the steam chamber, and the steam chamber is forced to expand laterally along the interlayer to form a steam chamber similar to an inverted triangle. The steam chamber is fully developed in the area below the interlayer, but the steam chamber cannot break through the interlayer.

Theoretical Study on Quantitative Characterization of Interlayer Interference in Multi-Layer Commingled Production

X oilfield is a typical layered reservoir with a large vertical span and many oil-bearing formations. There are significant differences in reservoir types and fluid properties among various formations. The interlayer interference is severe in the development process. At present, the interlayer interference research based on dynamic monitoring data cannot meet development adjustment needs. Combined with the field test results, through the indoor physical simulation experiment method, dynamic inversion method, and reservoir engineering method, this paper analyzes the main control factors and interference mechanism of interlayer interference, studies the variation law of interference coefficient, improves and forms the quantitative characteristic Theory of interlayer interference in multi-layer commingled production, and provides theoretical guidance for the total adjustment of the middle strata division in the oilfield.

Effects of oil viscosity on waterflooding: A case study of high water-cut sandstone oilfield in Kazakhstan

AbstractAfter a sandstone oilfield enters the high water-cut period, the viscosity of crude oil has an important influence on remaining oil distribution and waterflooding characteristics under the same factors of, e.g., reservoir quality and development methods. Based on a comprehensive interpretation of the waterflooded layers in new oil wells, physical simulation experiments, and reservoir numerical simulations, we analyzed the waterflooding laws of a high water-cut sandstone reservoir with different oil viscosities in Kazakhstan under the same oil production speed, and we clarified the remaining oil potential of reservoirs with different viscosities and proposed corresponding development measures. The results show that low-viscosity oil reservoirs (1 mPa s) have uniform waterflooding, thick streamlines, small waterflooding areas, and low overall waterflooding degrees because of their homogeneous oil–water viscosities. However, within waterflooded areas, the reservoirs have high oil displacement efficiencies and high waterflooding degrees, and the remaining oil is mainly concentrated in the unwaterflooded areas; therefore, the initial production and water cut in new oil wells vary significantly. High-viscosity oil reservoirs (200 mPa s) have severe waterflooding fingering, large waterflooding areas, and high overall waterflooded degrees because of their high oil–water mobility ratios. However, within waterflooded areas, the reservoirs have low oil displacement efficiencies and low waterflooding degrees, and the remaining oil is mainly concentrated in both the waterflooded areas and the unwaterflooded areas; therefore, the differences in the initial production and water cut of new oil wells are small. Moderate-viscosity oil reservoirs (20 mPa s) are characterized by remaining oil distributions that are somewhere in between those of the former two reservoirs. Therefore, in the high water-cut period, as the viscosity of crude oil increases, the efficiency of waterflooding gradually deteriorates and the remaining oil potential increases. In the later development, it is suggested to implement the local well pattern thickening in the remaining oil enrichment area for reservoirs with low viscosity, whereas a gradual overall well pattern thickening strategy is recommended for whole reservoirs with moderate and high viscosity. The findings of this study can aid better understanding of waterflooding law and the remaining oil potential of reservoirs with different viscosities and proposed corresponding development measures. The research results have important guidance and reference significance for the secondary development of high water-cut sandstone oilfields.

Experimental study on the diffusion characteristics of polyurethane grout in a fracture

Although polyurethane grouting has been widely used in fractured rock masses, the understanding of polyurethane diffusion characteristics still needs to be enhanced significantly. To analyse the diffusion mechanism of the polyurethane grout in the fracture, physical simulation experiments were conducted using a self-designed device. Additionally, the influence of grouting quantity on the grout diffusion distance and pressure distribution was investigated. The results indicated that the diffusion radius and pressure field increased with the increase in grouting quantity. Furthermore, the pressure growth rate and grout diffusion rate during the early self-expansion stage is directly proportional to the amount of polyurethane grout injected. However, the change in grout pressure is not synchronised with that of the diffusion radius. Hence, a hysteresis effect was observed for the pressure field change. Additionally, the grout pressure, which was not distributed evenly, decreased along the diffusion radius as it moved away from the grout hole. Furthermore, we derived the relationship between maximum diffusion radius and grouting quantity. Therefore, this study provides a better understanding of the diffusion law of polyurethane grouting in fractured rock masses.

Experimental Study on the Cyclic Steam Stimulation Assisted by Flue Gas Under Shallow Heavy-Oil Reservoir Conditions: Optimization of the Steam-Flue Gas Ratio

Normally, the recovery effect of a heavy-oil reservoir gradually deteriorates after multiple rounds of cyclic steam stimulation (CSS). However, the injection of flue gas can effectively increase the utilization degree of steam heat energy, which improves the recovery effect. In this paper, an experimental method for CSS using an energy storage container was established. Based on this method, a one-dimensional core physical simulation experiment for CSS under different flue gas ratios was performed. During the experiment, the changes in temperature field, oil production rate, increase in backpressure, and oil recovery factors were tested. In addition, differences in these data under different injection steam-flue gas ratios were compared. The results show that the flue gas provides a channel of fluids in porous media for steam, which is conducive to the heat transfer of steam to the deeper part of the sandpack. The sandpack has a higher temperature in each cycle than the CSS. The core temperature of each round of flue-gas-assisted CSS is higher than that of the CSS. The final oil recovery factors of flue-gas-assisted CSS using different steam-flue gas ratios are 22.2, 26.7, 30.8, 24.4, and 21.6%, while that of CSS is only 17.2%. According to the experiment, it is concluded that the best steam-flue gas ratio to optimize the flue-gas-assisted CSS is 1:10. With the combined effect of three factors (the temperature field of the sandpack, energizing effect of the flue gas, and degree of oil during recovery), the flue-gas-assisted CSS using the steam-flue gas ratio of 1:10 maximizes the steam heat transfer, increases the energy of return discharge, replenishes formation energy, and improves the oil recovery factor. Through the experiment, the research results provide theoretical guidance for improving the effectiveness of the CSS of heavy-oil reservoirs.

Geometric Model for Physical Simulation System of Coal and Gas Outburst

The physical simulation system is an important means to study the mechanism of coal and gas outburst. The small- and medium-sized coal and gas outbursts account for the largest proportion in China. So, the paper focuses on small- and medium-sized coal and gas outbursts based on key physical rules and their statistical characteristics. According to the geometric parameters statistical data of more than 100 caverns, the proportion of outburst caverns whose depth is less than 5 m is 80%, and whose depth is more than 6 m is 13%. The ratio of depth and cavern outlet’s diameter is 2.58–7.31. There are statistical relationship of 2 times between coal’s and cavern’s volume, and between gas emission volume per ton and gas content in seam. Then, the cavern of coal and gas outburst is simplified as an ellipsoid, and the shape of cavern outlet is simplified as a circle. The cavern’s and the prototype’s geometrical parameters of small and medium coal and gas outbursts were deduced. The depth of cavern is 5 m, width is 4 m, and diameter of cavern outlet is 0.68–1.94 m. The depth of coal and outburst prototype is 12.3 m, width is 6.5 m, and diameter of cavern outlet is 0.68 m. In order to guarantee the movement similarity, according to the relationships among statistical data of outburst coal particle’s size, cavern outlet’s size, and height of tunnel, the minimum cavern outlet’s size was calculated. Select 10 times the coal particle’s size (5 mm) as the smallest size. Then, maximum geometric similarity ratio of coal and gas outburst was deduced, and it is 13.6. The minimum geometrical parameters of coal and outburst similar model were obtained. Its depth is 0.9 m, width is 0.48 m, and diameter of cavern outlet is 50 mm. According to the results, the physical simulation system was developed. The results provide support to carry out physical simulation experiment of coal and gas outburst.

Study on the Mechanism and Control of Rock Burst of Coal Pillar under Complex Conditions

In order to explore the mechanism of coal pillar rock burst in the overlying coal body area, taking W1123 working face of Kuangou Coal Mine as the engineering background, the full mining stage of W1123 is simulated by FLAC3D. It is found that the high stress concentration area has appeared on both sides of the coal pillar when W1123 does not start mining. With the advance of the working face, the high stress concentration area forms X-shaped overlap. There is an obvious difference in the stress state between the coal pillar under the solid coal and the coal pillar under the gob in W1123. The concrete manifestation is that the vertical stress of the coal pillar below the solid coal is greater than the vertical stress of the coal pillar below the gob. The position of the obvious increase of the stress of the coal pillar in the lower part of the solid coal is ahead of the advancing position of the working face, and the position of the obvious increase of the stress of the lower coal pillar in the gob lags behind the advancing position of the working face. At the same time, in order to accurately reflect the true stress environment of coal pillars, the author conducted a physical similarity simulation experiment in the laboratory to study the local mining process of the W1123 working face, and it is found that under the condition of extremely thick and hard roof, the roof will be formed in the gob, the mechanical model of roof hinged structurer is constructed and analyzed, and the results show that the horizontal thrust of roof structure increases with the increase of rotation angle. With the development of mining activities, the self-stable state of the high stress balance in the coal pillar is easily broken by the impact energy formed by the sudden collapse of the key strata. Therefore, the rock burst of coal pillar in the overlying coal body area is the result of both static load and dynamic load. In view of the actual situation of the Kuangou Coal Mine, the treatment measures of rock burst are put forward from the point of view of the coal body and rock mass.

Multifield Coupled Dynamics of Power Supply Arc Based on Image 3D Reconstruction Mathematical Model

During the conversion process of the short-circuit arc to the submerged power supply arc, because the short-circuit arc diameter is much larger than the submerged power supply arc, the specific position of the submerged power supply arc cannot be determined, and the initial position of the submerged power supply arc has a certain randomness. The purpose of this paper is to try to use the binocular stereo vision method to reconstruct the submerged arc image in three dimensions, obtain the moving image of the arc, obtain more comprehensive information than the two-dimensional image, and multi-field coupling dynamics of the power supply arc. In this paper, the multi-field coupling effects of electromagnetic force, thermal buoyancy, wind load and air resistance of the submerged arc of the half-wavelength transmission line are considered comprehensively, and the chain arc model is incorporated into the force equation and motion model of the submerged arc. By deeply analyzing the formation and motion mechanism of the arc root, the arc root model of the submerged power arc is established, and the optimal selection method of the current element length is proposed. The physical simulation experiment of the half-wavelength submerged arc is carried out, and the simulation results are compared with the experimental results to verify the effectiveness of the simulation model. By comparing the trajectory and self-extinguishing time of different submerged currents, wind speeds and winds to the submerged power supply arc, the effects of wind load, thermal buoyancy and electromagnetic force on the arc are analyzed, which indicates that the built arc model can effectively account for the wind load. The influence of submarine power arc motion and self-extinguishing characteristics. The results show that the submarine power arc image is acquired by constructing a binocular stereo vision system, and the obtained submersible arc image is reconstructed three-dimensionally. The three-dimensional image of the arc is obtained and compared with the actual image. The result shows that the three-dimensional reconstruction The result is effective, and the exploration study provides a new method for further obtaining the multiple variations of the true arc length of the arc with the arcing time.

Large physical simulation and optimum parameter determination of stimulated reservoir volume (SRV) of a tight reservoir in E’nan

Studies have demonstrated that the real hydrofracturing in fractured reservoirs will not all form symmetrical fracturing in classical theory; however, they will rather form a complex fracture network. The changes in geostress because of the existence of natural fractures are an important reason for this phenomenon. At present, there are systematic theories and methods for examining the extension of hydraulic fractures after intersecting with natural fractures. Moreover, there is little or no quantitative research on specific parameters reported in the literature. However, the results are not applicable to actual field exploitation. Based on previous studies, this study proposes an improved model for hydraulic fractures after intersecting with natural fractures. Using the Honghe 92 well area in E’nan reservoir as the test case, the intersection chart of the block was drawn to analyze the extended model of hydraulic fracture. In this study, the true triaxial physical simulation experiment is reported and a comparison was made to demonstrate the correctness of the intersection chart. The fracturing simulation of Honghe 92 well area in E’nan reservoir was conducted to optimize the construction parameters and construction suggestions were put forward for the well area. The research results provide a theoretical basis and parameter guidance for the actual exploitation design of the oilfield. Furthermore, the results obtained will be helpful in improving the effect of SRV and increase oilfield productivity.

Physical simulation experiment on porosity evolution and controlling factors of Miocene reservoir in Ledong-Lingshui Depression, Qiongdongnan Basin, South China Sea

Considering the high-temperature and overpressure in Miocene reservoirs of Ledong-Lingshui Depression, physical simulation experiments and other methods were adopted to identify the effect of overpressure on reservoir quality and the controlling factors of high-quality reservoir in porosity evolution process. In this paper, the temperature-pressure fields were divided into high-temperature normal-pressure (HTNP) zone, high-temperature overpressure (HTOP) zone, and high-temperature high-overpressure (HTHO) zone. The research findings are as follows: (1) The overpressure has a certain protective effect on primary pores. The visible porosity obtained from overpressure compaction simulation experiment is much higher than that obtained from normal compaction simulation experiment in the same diagenetic stage. The differences of visible porosity between normal compaction and overpressure compaction and high overpressure compaction can reach 1.55% and 6.74% respectively. (2) The organic acid dissolution contributes greatly to the formation of secondary pores in reservoir. The difference of visible porosity between organic acid dissolution and normal compaction is 0.96–7.38%. But the meteoric water leaching has a limited impact on reservoir porosity with a difference of merely 0.19% between meteoric water leaching and normal compaction. (3) Organic acid dissolution has the greatest constructive effect on diagenesis under the HTNP. However, overpressure protection to primary pores is the leading contributor to high-quality reservoir under the HTOP and HTHO, and the protective effect is positively correlated with the increase of overpressure. Overall, this work provides new insights into the porosity evolution and controlling factors in reservoirs.

Physical simulation experiment on prevention and control of water inrush disaster by backfilling mining under aquifer

Solid backfill coal mining technology can be safely and efficiently used to exploit coal resources under aquifers, without causing harm to the water resources and the environment. Nevertheless, the mechanism of fracture development and seepage channel or pathway control in the key aquiclude strata (KAS) in backfill coal mining under fluid–solid coupling have not been studied. Based on the similarity theory of fluid–solid coupling physical simulation, this study involves experimental evaluation of similar materials and characteristics of composite KAS, backfill body, and aquifer. Subsequently, we designed and employed three experimental models for physical simulation, corresponding to backfill materials’ compaction ratios (BMCRs) of 0%, 65%, and 80% using the geological conditions of mining face No. 101 under the aquifer in the Wugou coal mine. Fracture evolution laws, mining-induced deformation, and stress distribution characteristics of composite KAS with different BMCRs are studied. The backfill body can effectively weaken the influence of mining stress, such as the maximum subsidence, sinking speed, initial or periodic fracture damage area of the composite KAS, inhibiting the formation of seepage cracks and water inrush channels. The increase in the BMCR plays an important role in the closure and repair of developed fractures.

A New Type of Gelled Foam Plugging Agent with Resistance to Temperature, Salt and Dilution

The conventional foam plugging agent is susceptible to factors such as dilution of formation water, high temperature and high salinity, which usually shortens its effective period and undermine its application. Based on conventional foam plugging agents, an anti-dilution gelled foam plugging agent suitable for oil reservoirs with high temperature and high salinity is proposed in this paper. The research results show that the density of the gelled foam plugging agent (0.6∼0.9 g/cm3) is controllable and easy to prepare, and it can be stabilized at 130° and 2.2 × 105mg/L mineralization for at least 72 h. The indoor physical simulation experiments show that the plugging rate of gelled foam plugging agent is more than 98%, and the plugging effect is obvious, showing a good channeling plugging capability.

Effects of matrix permeability and fracture on production characteristics and residual oil distribution during flue gas flooding in low permeability/tight reservoirs

The effects of matrix permeability and fracture on production characteristics and residual oil distribution of flue gas flooding in low permeability/tight conditions are analyzed systematically by laboratory physical simulation experiments and low-field nuclear magnetic resonance (LFNMR) system. T2 spectra results show that the crude oil is mainly distributed in the corresponding macropores of 100–1000 ms before and after the flue gas injection, and the crude oil in macropores is produced in large quantities after the flue gas injection in both fracture and fracture-free low permeability/tight cores. Additionally, oil production performance indicates that matrix permeability has a remarkable effect in fracture-free low permeability/tight cores. T2 spectra combined with slice scanned images show the migration from the macropores to the medium and fine pores is more obvious in the core with high matrix permeability and the final residual oil distribution is more uniform compared to those of the core with low matrix permeability. Matrix permeability is inversely proportional to the gas channeling point and it has a linear relationships with the gas channeling point in a log-log plot in fracture-free low permeability/tight cores. Besides, fracture can significantly reduce the effect of matrix permeability on oil recovery. The presence of fracture weakens the migration of crude oil in low permeability/tight fracture cores, and the residual oil spreads throughout the core. Fracture plays a dominating role in the gas channeling points for different permeability cores.

Physical simulation experiments of remaining oil distribution and production in alluvial fans controlled by dynamic and static factors

In order to study the remaining oil distribution and production in alluvial fans controlled by both static geologic factors and dynamic development factors, 2D and 3D macroscopic physical models have been constructed for the alluvial fan reservoirs in the eastern part of Cangdong sag, Bohai Bay Basin, China. Through considering static reservoir architecture and dynamic displacement rate, perforation position, well type, and well pattern, 7 water flooding physical simulation experiments have been finished, and the remaining oil distribution and production in oilfields with ultra-high water cut controlled by both dynamic and static factors were revealed. The study shows that without considering the economic benefits, drilling horizontal well, drilling infilled vertical well, increasing displacement rate, and plugging off water flooded layers at the initial stage of ultra-high water cut exhibited decreased performance in remaining oil production. After the dynamic factors adjustment, the remaining oil distribution and production is mainly controlled by the interlayer position, reservoir rhythm and the combination relationship between dynamic and static factors. When more injector-producer groups are located in the same single sand body, and the oil wells are uniformly drilled in single sand of different types, the oil recovery efficiency will be higher, and the distribution of the remaining oil will be more uniform. According to the experimental results, the remaining oil controlled by braided sand island and braided river channel could be divided into three types, and the corresponding measures to tap the potential were proposed.

Karst Water Pressure’s Varying Rule and Its Response to Overlying Strata Movement in Coal Mine

Karst water is widespread throughout China and is heavily influenced by complex geological conditions, and floor inrush of karst waters associated with coal seams is the second most common coal mine disaster in China. Due to the limitation of precision and cost of geophysical exploration technology, the volume and pressure of karst water are challenging to measure, especially during the mining process. Therefore, predicting karst pressure’s response to mining is critical for determining the mechanism of water inrush. Here, closed karst water pressure (CKWP) response to mining was studied in an innovative physical simulation experiment. In the simulation experiment, a capsule and a pipe were designed to reflect CKWP and the water level. In the experiment, the vertical stress and karst water level were monitored throughout the process of an advancing coal panel. Monitoring results show that the range of the abutment pressure was about 40 cm, and the peak coefficient value was about 2. When the working face is far away from the water capsule, the stress and water column near the water capsule have no obvious change. With the working face 10 cm from the water capsule, the stress and water column height increased significantly. When the working face was right above the water capsule, the stress and water column rose sharply and reached the maximum value. When the working face advanced beyond the water capsule, the stress and water column height declined. Through establishing a structural mechanics model, the karst water system underneath the working face is assumed to be a hydraulic press. Accordingly, the compressed area was assumed to be a piston. The karst water pressure increases sharply, while the piston is compressed, increasing water inrush risk. This discovery may help determine the water inrush mechanism from a novel point of view.