Physical Simulation Experiments Research Articles

Microscopic Mechanism of Variations in Physical Parameters of Natural Gas Containing CO2 at Ultrahigh Temperature and High Pressure.

Owing to limitations imposed by the experimental requirements, it is difficult to carry out pressure–volume–temperature experiments on CO2-containing natural gas in high-temperature and ultrahigh-pressure gas reservoirs. Relevant research is also insufficient, which has led to a lack of clarity in current understanding of the microscopic mechanism of variations in the deviation factor of high-CO2 natural gas under high-temperature and ultrahigh-pressure conditions. This has greatly limited the development of natural gas reservoirs containing CO2. To reveal the microscopic mechanism of variations in the deviation factor of natural gas containing CO2 as a function of pressure under high-temperature and high-pressure conditions, by physical simulation experiments, the deviation factors of samples of sour natural gas with known CO2 contents from the Ledong gas reservoir were determined. Then, according to the idealized parameters of the physical experiment, a molecular model of natural gas containing CO2 was established using molecular simulation methods. Changes in molecular density, molecular volume, nonbonding interaction energy, potential energy, and kinetic energy during variations in the deviation factor of a CO2-containing natural gas system as a function of pressure under high-temperature and ultrahigh-pressure conditions were quantitatively studied. Using molecular simulation techniques, it was found that the changes in total energy, kinetic energy, and potential energy between molecules are the internal factors that cause variations in the deviation factor of natural gas systems containing CO2 under ultrahigh-temperature and high-pressure conditions. The results show that the increase of carbon dioxide content in natural gas will cause the total energy of natural gas molecules to decrease when the pressure is constant. This means that the higher the CO2 content in natural gas, the easier it will be compressed. This study should lay the foundation for investigating the mechanisms of the occurrence of CO2-containing natural gas, as well as facilitating the exploitation of CO2-containing natural gas.

Feasibility analysis of a single-well retreating horizontal cavern for natural gas storage in bedded salt rock

Compared with vertical storage, horizontal storage in bedded salt rock deposits is reasonable and scientific for large-capacity gas storage and for avoiding the risk of interlayer and interfacial oil and gas leaks. The single-well retreating horizontal (SWRH) leaching method is introduced in this paper. After calculating similarity ratios, a physical similarity simulation experiment was conducted for inferring the cavern shape. A numerical model was developed based on the inferred cavern shape, and the stability of the SWRH cavern was analysed. Reasonable values of the cycle frequency and the roof and floor salt layers’ thicknesses were determined. The effects of the pillar width and asynchronous internal gas pressure between adjacent caverns were analysed. The results show that the SWRH cavern satisfies the safety requirements of bedded salt rock districts over the entire design lifetime. A cyclic frequency that is too low and asynchronous internal gas pressure are not conducive to the stability and reliability of the cavern. To ensure stability, the thicknesses of the roof and floor salt rock layers of the horizontal cavern should exceed 16 m and 6 m, respectively. This study opens new vistas for constructing horizontal gas-storage systems in bedded salt rock.

Parameter Measurement of Edible Sunflower Exudates and Calibration of Discrete Element Simulation Parameters

To improve the accuracy of the parameters used in discrete element simulation tests in the process of clearing fresh sunflowers, this study took the extracts of fresh sunflower as the research object and used a combination of physical experiments and simulation experiments to calibrate the discrete element simulation parameters. First, the composition of the edible sunflower extract is determined, and then, the physical test method is used to determine the characteristics of the edible sunflower extract material. Based on the results of the physical test as a simulation basis, the Plackett–Burman test is used to screen the significance of the test parameters, and the screening results show that the shear modulus, static friction coefficient, and collision recovery coefficient of sunflower kernels have significant effects on the simulated angle of repose. On the basis of the steepest climbing test, the Box–Behnken test is carried out to obtain the simulated angle of repose and significance. The second-order regression equation of texture parameters is optimized with the actual physical angle of repose (24.68°) as the target value to obtain the optimal parameter combination. Finally, through the two-sample T test, p > 0.05 is obtained, indicating that the simulated angle of repose and the actual physical test angle of repose are not significantly different, and the relative error is 0.923%, which verifies the reliability of the optimal simulation parameter combination. The research results show that the calibrated simulation parameter combination can be used in discrete element simulation tests of the extraction process of sunflower extracts.

Physical simulation study on grouting water plugging of flexible isolation layer in coal seam mining

Deep coal seam mining often leads to water resource loss due to bedrock water entering the workings of the mine and is discharged adjacent to the mining area. Using the geological conditions of the Maiduoshan coal mine, this paper applied a physical simulation experiment. The specified rock above the coal seam was hydraulically fractured in advance to form a postmining grouted fracture network, followed by grouting to construct a flexible isolation layer that blocked the infiltration of groundwater from the aquifer into the water-conducting fracture zone. Stress sensors, flow sensors and strata displacement monitoring technology were deployed inside the experimental material to study the spatial distribution characteristics and evolution law of the water-conducting fracture zone in the overlying rocks. Analysis of the water-conducting fracture zone development law, stress variation, overburden evolution characteristics, fracturing and grouting sequence of the flexible isolation layer and the effect of postmining grouting on the water barrier was conducted. These experiments verified the feasibility of fracture and grouting of the flexible isolation layer. These research results will provide practical guidance for the transition from the current safe and efficient mining methods to safe and green mining methods of deep coal mining in the western mining areas of China.

Compatibility characteristics of fracturing fluid and shale oil reservoir: A case study of the first member of Qingshankou Formation, northern Songliao Basin, Northeast China

Hydraulic fracturing is currently one of the most economical and effective means to develop shale oil resources. However, the fracturing effects in shale oil wells vary significantly. The compatibility between the fracturing fluid and the shale oil reservoir is one of the important factors affecting the fracturing stimulation. In this study, a series of physical simulation experiments were carried out to reveal the changes in the physical properties and surface properties of a shale oil reservoir using different fracturing fluids (guar gum fracturing fluid, slick hydraulic fracturing fluid, and formation water fracturing fluid). The dynamic flowback process of different fracturing fluids was visualized and quantitatively characterized using the NMR technology. The results indicate that with the increase in soaking time in the formation water fracturing fluid, the hysteresis coefficient of the shale increased. The increasing ink-bottle pores resulted in worse pore connectivity and physical properties of reservoir. The shale undergoes strong water sensitivity damage and strong stress sensitivity, which is not conducive to the stability and long-term effects of shale oil production. After injecting the guar gum fracturing fluid, the pore connectivity of the shale is enhanced, and the stress sensitivity is the weakest. The particle suspension and dispersion system of the guar gum fracturing fluid is the most stable, which greatly avoids reservoir damage caused by solid particle migration blocking in the pore throat. In addition, it can effectively inhibit shale hydration and expansion, and achieve the highest displacement flowback efficiency, which is more suitable for the fracturing operation of shale oil reservoirs in the study area. The effects of the slippery hydraulic fracturing fluid on shale are between the above two fracturing fluids. The research results are of great significance in guiding the fracturing operation of shale oil wells in the northern Songliao Basin.

NMR Analysis Method of Gas Flow Pattern in the Process of Shale Gas Depletion Development

Shale gas reservoirs have pores of various sizes, in which gas flows in different patterns. The coexistence of multiple gas flow patterns is common. In order to quantitatively characterize the flow pattern in the process of shale gas depletion development, a physical simulation experiment of shale gas depletion development was designed, and a high-pressure on-line NMR analysis method of gas flow pattern in this process was proposed. The signal amplitudes of methane in pores of various sizes at different pressure levels were calculated according to the conversion relationship between the NMR T 2 relaxation time and pore radius, and then, the flow patterns of methane in pores of various sizes under different pore pressure conditions were analyzed as per the flow pattern determination criteria. It is found that there are three flow patterns in the process of shale gas depletion development, i.e., continuous medium flow, slip flow, and transitional flow, which account for 73.5%, 25.8%, and 0.7% of total gas flow, respectively. When the pore pressure is high, the continuous medium flow is dominant. With the gas production in shale reservoir, the pore pressure decreases, the Knudsen number increases, and the pore size range of slip flow zone and transitional flow zone expands. When the reservoir pressure is higher than the critical desorption pressure, the adsorbed gas is not desorbed intensively, and the produced gas is mainly free gas. When the reservoir pressure is lower than the critical desorption pressure, the adsorbed gas is gradually desorbed, and the proportion of desorbed gas in the produced gas gradually increases.

Experimental investigation on the fracture propagation of three-stage acid fracturing of tight sandstone gas reservoir

The three-stage acid fracturing technology is an effective technology for tight sandstone reservoirs with undeveloped natural fractures. Its filed test has achieved good results in the tight sandstone field test in the Daning block of China. The core of this technology is to complete the pump injection procedure of “conventional fracturing, acid fracturing and conventional fracturing” in sequence. However, fracture propagation behaviors vary greatly under different acidizing fracturing conditions. In this paper, the influence of different factors on the uneven degree of hydraulic fracture etching and fracture propagation was studied by triaxial hydraulic fracturing physical simulation experiment. The effects of different acid concentration, acid dosage and acid reaction time on fracture propagation behaviors were analyzed. The results show that the fractures formed by the fracturing with displacement of 160 mL/min in the laboratory did not penetrate the overburden and underburden, and longer fractures and small branch fractures were formed in the reservoir. Hydraulic fractures showed a trend of continuous expansion in the sandstone reservoir, indicating that the fracturing effect was favorable. The experimental displacement is converted to the field displacement of 8 m3/min. The influence degree of acid concentration, acid dosage, acid reaction time on fracture propagation of three-stage acidizing fracture decreases in turn. Acid concentration and acid dosage are positively correlated with the area of fracture propagation. The influence of acid injection reaction time on fracture propagation is the lowest, and the influence of acid injection reaction time on fracture propagation area is significant only in the case of high acid dosage or high acid concentration. The influence of acid immersion time on fracture permeability is far less than that of acid concentration on fracture permeability. However, the greater the acid concentration, the greater the impact of acid immersion time on fracture permeability. The experimental results can provide empirical reference for the on-site construction of the three-stage acid fracturing in tight sandstone reservoirs.

Construction simulation of large-spacing-two-well salt cavern with gas blanket and stability evaluation of cavern for gas storage

The single well or small-spacing two-well technologies with oil blanket has been gradually applied to construct salt cavern storage in recent years. In order to solve the problems of low efficiency, oil blanket sealing failure, cavern deformity, roof collapses, small volume and brine pollution in salt cavern construction. In this study, a large-spacing two-well (Wellhead spacing is greater than 20 m) with gas blanket (LSTW-GB) method was proposed to construct salt cavern. Firstly, through indoor physical simulation experiment, the feasibility of the LSTW-GB to construct cavern is verified and discussed. The experimental results show that increasing the two-well-spacing effectively increases the effective cavern volume, improve the cavern construction rate and obtain clear brine, but the increase of two-well-spacing will also increase the difficulty of connecting the two wells, so more attention should focus on the technology improvement on connecting the two wells. Secondly, combined with the experimental observations and field geological data in Jintan bedded salt rock of China, the stability of the LSTW-cavern for gas storage under different ratios of long axis to height (RLH) was analyzed by numerical simulations. The simulation results show that as the RLH increasing, the stability of the LSTW-cavern gradually decreases. In addition, under low-internal-pressure operation, the cavern is most likely to lose its stability, so much more attention should be paid to designing the value and duration of minimum operating internal pressure (Pmin). Finally, the working conditions of the LSTW-cavern gas storage are optimized, and it is proposed that the Pmin of the gas storage in the LSTW-cavern should be 33% ∼ 38% of the gravity stress at the casing shoe when RLH varies from 1.60 to 3.10. Comprehensive research results show that the LSTW-cavern has a good application prospect in the construction of gas storage of salt rock in China.

The Law and Mechanism of the Sample Size Effect of Imbibition Oil Recovery of Tight Sedimentary Tuff.

Imbibition is an important mechanism to improve the recovery factor (RF) of a tight oil reservoir. Accurately evaluating the oil production capacity of tight oil reservoirs by imbibition is of great significance for the formulation of oilfield production plans and productivity prediction. However, there is currently no unified regulation on the selection of rock sample size in tight oil reservoir imbibition evaluation experiments, resulting in great differences in reservoir imbibition oil production capacity obtained from rock samples of different sizes, which brings great challenges to the efficient development of tight oil reservoirs. To clarify the law and mechanism of the rock sample size effect of tight core imbibition oil recovery, this paper takes the newly discovered tight sedimentary tuff (TST) oil reservoir as an example. First, several representative real cores were collected. Then, their wettability and pore structure characteristics were analyzed. Finally, physical simulation experiments of imbibition under different rock sample sizes were conducted. The results show that the TST has very favorable imbibition conditions, which are manifested in the following: (i) the wettability is weakly hydrophilic to hydrophilic; (ii) the mineral composition is tuffaceous minerals, calcite, and quartz, without clay minerals; (iii) micro-nanoscale pores are developed; and (iv) the pore throats are evenly distributed. In the imbibition experiments of rock samples of different sizes, the oil production characteristics of the core surface, the variation form of imbibition rate, pore production characteristics, and the influence mode of imbibition pressure on imbibition do not have the sample size effect. However, the RF of the spontaneous imbibition has an obvious sample size effect, and there is a good exponential function relationship between the imbibition RF and the specific surface area (SSA) of cores. The fundamental reason why the rock sample size effect of the TST imbibition oil recovery is relatively stable and has strong regularity is that its pore structure and wettability are relatively homogeneous and stable. The change of rock sample size does not have a great impact on the distribution of the core pore structure and wettability, resulting in no significant change in its imbibition power, resistance, and distance. Therefore, the main factor determining the imbibition RF of rock samples with different sizes is their SSA. The research results of this work can provide an important theoretical basis for understanding the law and mechanism of TST imbibition oil recovery and unifying the imbibition experimental results of small-sized rock samples.

Oil charging pore throat threshold and accumulation effectiveness of tight sandstone reservoir using the physical simulation experiments combined with NMR

Tight oil as a significant part of unconventional resources is now considered as one of most important alternative resources. Oil accumulation mechanism is still a research focus for the tight oil. Therefore, it is important to study the effectiveness of micro-nano pore system to oil charging and accumulation. Taking the Chang 7 tight sandstone reservoir of the Ordos Basin as an example, the physical simulation experiment of oil charging is applied to study the pore throat threshold of tight sandstone reservoir under the different charging force using the nuclear magnetic resonance (NMR) combined with displacement techniques. The relationship between charging force and pore throat radius threshold (Rth) can be established when combined with the pore throat distribution derived from MICP. In addition, the effectiveness of oil accumulation for the different type tight sandstone reservoir is also discussed. The result shows that the Chang 7 tight sandstone reservoir is divided into four groups based on pore structure and petrophysical property (porosity and permeability). In the physical simulation experiment, the oil saturation growth trend can be roughly divided into three groups: uniform growth model, slow growth-stable model, fast-slow growth model. This result indirectly reflects the heterogeneity of pore structure. There is a power function relationship between the charging force and Rth of oil charging, which can be used to calculate the effective accumulation space and further determine the accumulation effectiveness. The effectiveness of oil accumulation changes with the increase of the charging force: the effective accumulation space increases with the charging force, which causes that the reservoir (usually not including type III) gradually transits from ineffective accumulation to effective accumulation. That is, the charging force coupled with pore throat radius controls oil charging and accumulation. For the Chang 7 tight oil accumulation, the effective pore throat radius threshold of oil charging is about 0.1 μm and thus only the type I and II1 reservoirs can become the effective tight oil reservoirs, which is the main target of tight oil exploration. This result not only puts insight into the tight oil accumulation mechanism but also plays an important role in the tight oil exploration of Yanchang Formation in the Ordos Basin.

Experimental research on inter-fracture asynchronous injection-production cycle for a horizontal well in a tight oil reservoir

One of the existing tight oil reservoir development methods is development after hydraulic fracturing of horizontal wells. This type of development method severely limits the recovery rate of tight oil reservoirs. The other conventional enhanced oil recovery methods are not suitable for tight oil reservoirs. The water injection performance of fractured vertical wells is poor, and water breakthrough easily occurs during water injection in horizontal wells. In order to improve the recovery factor of tight oil reservoirs and to achieve sustainable development of tight oil reservoirs, finding a suitable method of enhancing the recovery factor of tight oil reservoirs is the top priority. Based on the concept of periodic asynchronous water flooding to supplement energy between horizontal fractures, in this paper, an effective method of improving the recovery rate of tight oil reservoirs is discussed. Physical simulation experiments were designed to improve the recovery efficiency of horizontal wells with an inter-fracture asynchronous injection-production cycle (IFAIPC). The feasibility of the method was verified. Two different sets of experiments were designed: 1) the experiment that simulates a homogeneous reservoir with a section with two fractures (M1), and 2) an experiment that simulates a heterogeneous reservoir with three sections of four fractures (M2) and the fourth section with five fractures (M3). The results show that during the IFAIPC process, the permeability of the rock sample tends to decrease gradually. In particular, in the first five cycles, the permeability decreases significantly. Water injection becomes difficult as the permeability decreases, and there is a feasible critical value for water injection. In homogeneous reservoirs, water breakthrough is slow. The degree of recovery and the ultimate recovery rate before water breakthrough are high. The use of IFAIPC in heterogeneous reservoirs can effectively increase the swept volume and delay the rise of water saturation. The IFAIPC method can effectively improve the recovery of tight oil reservoirs by more than 10% in the first five injection-production cycles. The experiments confirm the feasibility and effectiveness of using the IFAIPC method in tight oil reservoirs.

Welded truss deformation under thermal influence

The article studies some deformation features of the full-scale physical model test of the 2000x400 mm rectangular welded truss at thermal influence ranging from 20 to 160°C. Numerical information based on the values of deformations at seven control points of the truss for chords and nodes was obtained as a result. A computer simulation experiment using SolidWorks software for similar impact parameters on truss was performed. Results comparison of full-scale physical model deformation and computer simulation experiments revealed its similarity. Experimental results can be used in determining the parameters of the stress-strain state of the elements of the trusses under simultaneous force and temperature effects.

Quantitatively study on imbibition of fracturing fluid in tight sandstone reservoir under high temperature and high pressure based on NMR technology

Reservoir fracturing is one of the main technical means to realize high-efficiency development of low-permeability tight reservoirs in oil fields. With the implementation of reservoir fracturing measures, the imbibition effect is produced after the interaction between fracturing fluid and rocks in oil reservoirs. It is of great guiding significance to study the imbibition mechanism of fracturing fluid and quantitatively evaluate the imbibition effect of fracturing fluid with different pore throats under different conditions for practical development. In this paper, to reveal the mechanism of fracturing fluid imbibition from a microscopic point of view, based on the simulation of high temperature and high-pressure reservoir environment, using nuclear magnetic resonance (NMR) technology and dynamic physical simulation experiments, we quantitatively evaluated the imbibition effect of fracturing fluid with different pore throats at different times and investigated the influence of permeability, wettability, and viscosity of fracturing fluid on imbibition effect of fracturing fluid. The results show that the scale of imbibition of fracturing fluid is between 0.10 ms–51.20 ms. Additionally, the imbibition rate is the fastest in the initial stage of imbibition. Furthermore, the imbibition takes place in micropores (0.10 ms–1.00 ms) first, and then enters mesopores (1.00 ms–10.00 ms), followed by macropores (>10.00 ms) as the reaction time goes on. Also, micropores (0.10 ms–1.00 ms) are the best contributors to the imbibition effect of fracturing fluid, and the imbibition effect tends to be stable at first, followed by mesopores (1.00 ms–10 ms), with the highest contribution, but its imbibition effect is relatively lagging. Last, the imbibition efficiency is positively correlated with permeability, negatively correlated with fracturing fluid viscosity. It is also related to wettability. The imbibition effect of hydrophilic type is better than that of oleophilic type. The more hydrophilic the rock is, the better the imbibition effect is, and the imbibition stability time of the hydrophilic type lags behind that of the oleophilic type.

Practice and cognition of effective water-flooding development mode in Gaotaizi block of ultra-low permeability reservoir

During nearly 25 years of water injection development in Gaotaizi reservoir of LHP oilfield, due to poor reservoir physical properties, poor adaptability of well pattern and difficulty in establishing effective displacement between oil and water Wells, linear water injection, infill adjustment and refracturing tests have been carried out successively. Although certain effects have been seen, the effects are short and unsatisfactory. In this paper, the microscopic pore structure, sensitivity and seepage characteristics of ultra-low permeability high platform reservoir are studied through core laboratory experiments. New technology of nonlinear test and low permeable physical simulation experiment, the research on the rules of the nonlinear characteristics of the reservoir fluid and the characteristics of movable oil through research has been clear about the dragon bubble oilfield high effective displacement distance platform layer, and the new fracturing technology and the development of the technology to adjust the organic combination, the displacement between well and well past into displacement between Wells and joint network, explore the ultra-low permeability reservoir to improve the single well production, new ways to improve the development effect, with the types of low permeability oilfield development effectively.

Low-Frequency Extrapolation of Prestack Viscoacoustic Seismic Data Based on Dense Convolutional Network

Low frequency information in seismic data can improve seismic resolution and imaging accuracy, enhance the quality of inversion, and play an essential role in imaging algorithms such as full-waveform inversion. Sufficiently low frequency data can avoid the cycle skipping phenomenon during full-waveform inversion. During seismic data processing, the protection and reconstruction for low frequency information are therefore of great importance. In this paper, we systematically investigate the extrapolation of pre-stack viscoacoustic seismic low frequency data using a dense convolutional network to effectively establish the nonlinear relationship between high and low frequency data, and realize the extrapolation and reconstruction of viscoacoustic 0-5 Hz low frequency data using 5-30 Hz high-frequency component. And the generalizability of the method for different influencing factors such as wavelets, noise, and models is analyzed using Marmousi2 velocity model forward data. It is demonstrated that the method has high robustness and can be applied to different situations, and the accuracy is higher than that of the traditional convolutional neural networks method. The feasibility of the low frequency extrapolation method based on dense convolutional network is also verified by synthetic data, physical experiment simulation data, and field data testing, and superior to the traditional convolutional neural networks method.

Prediction of favorable areas for oil accumulation in outer-source tight reservoirs under the control of lateral migration distance: A case study of the Baikouquan Formation, Mahu Sag, Junggar Basin, China

There is a starting pressure gradient (SPG) for oil migration in tight reservoirs (TRs), and the SPG and the migration force jointly control the migration distance of oil. The key factor of oil accumulation in the tight glutenite reservoir (TGR) of the Lower Triassic Baikouquan Formation (T1 b) in the Mahu Sag is whether the oil can be laterally charged into the TRs. To analyze the lateral migration distances of oil in TRs and predict the favorable accumulation areas for oil, we have carried out a physical simulation experiment of oil charging on glutenite reservoirs of T1 b for obtaining the SPG of oil migration and knowing the relationship between SPGs and the reservoirs’ physical property. According to the basin simulation, we have obtained the pressure evolution of the source-rock formation as well as reservoir formation and the physical property evolution of the reservoir. Finally, we have predicated the favorable oil accumulation areas through calculating the distribution characteristics of SPGs as well as the theoretical distances of lateral migration of oil during the key oil accumulation period and considering the theoretical distance of the lateral migration of oil as the main controlling factor. Our results suggest that there is a SPG in the TGR of the T1 b and that there is a power function relationship between the SPG and the permeability. The theoretical lateral migration distance of oil in T1 b during the key oil accumulation period was the farthest in the northern sag, which was gradually shortened to the east, west, and south. In class I favorable areas, the reservoirs have good physical properties where overpressure has developed; in addition, the lateral migration distance of oil is far. Therefore, these are the most favorable areas for oil accumulation.

Influence of proppant physical properties on sand accumulation in hydraulic fractures

The proppant accumulation form in fractures is related to the formation conductivity after fracture closure, also closely related to the production rate of oil/gas wells. In order to investigate the influence of proppant physical properties on sand accumulation in fractures, a particle–fluid coupling flow model is established based on the Euler two-fluid model. Geometric parameters of a fracture in tight oil wells are approximately scaled in equal proportion as the physical model, which is solved by the finite volume method. And the model accuracy is verified by comparing with the physical experimental simulation in the literature. Results show that the higher proppant concentration corresponds to the faster particle sedimentation rate, and the greater sand embankment accumulation as well. However, the fluid viscosity will increase, inhibiting proppant migration to the deep part of the fracture. Reducing proppant density and particle size will enhance the fluidization ability of particles, which is conducive to the migration to the deep fracture at the initial stage of pumping. But, it is not beneficial to have a desirable accumulation state in the middle and later pumping stage, so it is difficult to obtain a higher comprehensive equilibrium height.

Experiments and Analysis of the Hydraulic Fracture Propagation Behaviors of the Granite with Structural Planes in the Gonghe Basin

AbstractHydraulic fracture (HF) propagation behavior is significant when building enhanced geothermal systems (EGS). HF geometry is closely related to the structural planes (SPs) in hot dry rock (HDR), such as natural fractures (NFs), quartz veins (QVs) and lithologic interfaces (LIs). However, the HF behaviors in HDR have not been well understood, especially the influence of multiple SPs on the HF geometry. To clarify this mechanism, several groups of physical simulation experiments of hydraulic fracturing were conducted to investigate the intersection relationship between the HFs and the SPs. Results show that the HF geometry shows great differences when intersecting with different SPs. In summary, the HF geometry displays four basic patterns, namely, propagation along the SPs, branching, capture, penetration/non‐dilation. The fluctuation degree of the pressure‐time curve and the HF complexity show a positive correlation. The cementing strength of the SP and their different mechanical properties from rock matrix influence the HF behaviors significantly. Therefore, the HF shows diverse geometries when intersecting with the NFs and LIs, while propagating along the QV when intersecting with it. For the complex networks, it is favorable for the HF to penetrate through and dilate several SPs, rather than simply cross or propagate along the SP.

Experimental study on production performance and reserves utilization law in carbonate gas reservoirs

Carbonate gas reservoirs in China are rich in reserves. In the development process, there are many reserves with low permeability, low efficiency and low recovery degree. It is difficult to stabilize gas well production and prolong its life cycle. Under the condition of original water saturation (Sw) of 0%, 20%, 40%, 55% and 65%, respectively, the physical simulation experiment of gas reservoirs depletion development was carried out by using long core multi-point embedded pressure measuring system. The long cores with average gas permeability of 2.300 mD, 0.485 mD and 0.046 mD (assembled from 10 carbonate cores) were used to carry out this experiment. During the experiment, the pressure dynamics at different positions inside the long core and the gas production dynamics at the outlet were recorded in real time to reveal the production performance and reserves utilization law of carbonate gas reservoirs. The results show that the stable production period of tight reservoir in carbonate gas reservoirs is short, and the low production period is relatively long. The stable production time and recovery rate of gas reservoir increase with the increase of reservoir permeability and decrease with the increase of water saturation. The production of tight carbonate gas reservoirs with permeability less than 0.1 mD is greatly affected by pore water, and the reservoir pressure distribution shows a steep pressure drop funnel, and the reserves far from well are rarely used. Therefore, the reserves far from well should be utilized by closing well to restore formation pressure balance, densifying well pattern or transforming reservoir. The variation range of water saturation in the development of carbonate gas reservoirs is influenced by reservoir permeability and water saturation, and closely related to formation pressure gradient in production process. It decreases with the increase of reservoir permeability and increases with the increase of original water saturation. The research results provide a theoretical basis for understanding the relationship between physical properties of carbonate gas reservoirs and production performance, reserves utilization law, and realizing balanced utilization, efficient development and long-term stable production of carbonate gas reservoirs.

Scaled Model Simulation and Experimental Verification of Submarine Flexible Pipeline Laying System

In order to adapt to the complex and changeable marine environment such as wind, wave, and current, the physical simulation experiment is usually needed in the design of a deep-sea flexible pipeline-laying system. In reality, the flexible pipeline-laying system is very large, and the experimental cost is huge. Therefore, when analyzing this system, it is necessary to carry out scaled model experiments to verify the rationality of it. Taking the flexible pipeline-laying system working under four-level sea conditions as an example, this paper deduces the similarity criteria of the scaled model according to the similarity theory. According to the required experimental site, the sizes and materials of the model are selected, and then the physical quantities of the model and their similarity ratio corresponding to the prototype are determined. According to the physical quantities of the experimental model, the similarity of dynamic characteristics and structural strength between the model and the prototype are verified by Adams and ANSYS Workbench. The research shows that the scaled model and prototype based on similarity theory can meet the established similarity relationship, and the scaled model experiment is an effective way to verify the rationality of the design of a flexible pipeline-laying system.