查看更多>>摘要：The flow mechanism between the injector and producer is different from the flow in the steam chamber in the Steam-Assisted Gravity Drainage (SAGD) process. The interwell flow between the injector and producer is determined by both gravity and the pressure difference. In this study, the interwell flow model is improved by introducing a relative permeability model and an oil viscosity linearity assumption, considering the availability of input data. The interwell flow in the liquid pool is coupled with the gravity drainage in the steam chamber throughout the entire SAGD process. And the liquid level calculated by the new model is validated by field data. The results show that the subcool gradient is larger in the earlier stage and smaller in the later stage. The liquid level, subcool, pressure difference and wellbore liquid rate are interacted and should be matched to each other. In field applications, the subcool should be controlled differently according to its development stage. The subcool of the hottest spot should be near zero to maximize the well productivity and the steam chamber supply capacity. The results of this study provide theoretical guidance for the evaluation and adjustment of field dual-horizontal SAGD well pairs.
查看更多>>摘要：Understanding pore heterogeneity is essential to obtain insights into the gas storage, transport, and recovery from coal. The pore structure in analytical sample particles of different sizes varies significantly, leading to inaccurate pore characterization. In this study, we discuss the effect of particle size on the pore structures and multifractal characteristics of two samples with six particle sizes using low-pressure gas adsorption. The results show that, with decreasing particle size, the mesopore and macropore volumes and specific surface areas (SSAs) of the two samples fluctuate. The variations of micropores that contribute to most of the total pore volume and SSA (>90%) are different. Multifractal analysis shows that the subsamples with the smallest particle size have the most homogeneous pore structures and the highest pore connectivity. We reveal a negative power function relationship among particle size and pore volume, and SSA, indicating that crushing opens up more pores that were initially closed. The differences between the two coal samples may be caused by the combined effects of crushing and associated impacts (e.g., pore collapse), coalification, incomplete equilibration of N2 adsorption, and mineralogical inhomogeneity. Our results demonstrate that in the range of test particles, the finer the particle size used, the more accurate the evaluation of highly mature coal adsorption properties.
Tian, JieWang, LiangZhao, Rong RongLiu, Hong Qi...
10页
查看更多>>摘要：Porosity exponent (m) is a key parameter for calculating reservoir oil and gas saturation and evaluating reservoir effectiveness; the development of matrix pores, vug pores, and fractures makes the m response regularity of fractured-vuggy reservoirs unclear, which makes the accurate calculation of saturation difficult. By applying Maxwell-Garnett mixing rule to vuggy reservoirs and conductivity tensor analysis to fractured reservoirs, an improved Triple Porosity Model considering fracture dip angle is established. The newly improved Triple Porosity Model clarifies the response regularity of m to the matrix pores, vug pores, fracture pores, and fracture angles. Based on the improved Triple Porosity Model, the response regularity chart of m is further established. The findings show that: (1) m increases with the increase of fracture dip angle (theta) and the development of vugs; (2) m increases with the development of high-angle fractures and decreases with the development of low-angle fractures; (3) in fractured reservoirs, the fracture dip angle of 33 degrees is the critical dip angle that determines the relationship between m and matrix porosity exponent (m(b)); (4) an increase in matrix porosity will weaken the influence of vugs, fractures, and fracture dip angle on m, which will eventually make m converge to m(b). The field application of fractured-vuggy reservoirs shows that the water saturation calculated by the improved Triple Porosity Model is better in agreement with the core analysis results.
查看更多>>摘要：CO2 injection enhanced coalbed methane (CH4) recovery technology can achieve the enhancement of CH4 production and the effective geological storage of carbon dioxide in coal seams. A coal seam is composed of matrix and fractures. Matrix has open pores and closed pores and fractures may have stacked coal grains. However, the influences of closed pores in matrix and stacked coal grains in fractures on CO2 injection enhanced CH4 recovery have rarely been studied. This paper develops a numerical simulation model to explore the hydraulic-mechanical coupling responses in CO2 injection enhanced coalbed methane (CO2-ECBM) recovery process. This model considers the binary gas displacement and transport in ternary pores, the deformation of coal with different porosity, and fractal stacked coal grains in fractures. After verification with the data available from literature, this model is used to simulate a field trial in the Qinshui Basin. The simulation results show that the contribution of gas in closed pores to the total CH4 production enhanced by CO2 injection is more than 60% in high-rank coal and is proportional to the volume fraction of closed pores. The stacked coal grains in fractures affect the effective roughness and can be expressed by three structural parameters. Higher effective roughness induces lower cumulative CO2 injection and lower cumulative CH4 production and the conical bottom diameter of cone-like element has the largest influence. These findings can promote our understanding for the influence of closed pores and stacked coal grains on gas transport in coalbed gas reservoirs from a multi-scale perspective.
查看更多>>摘要：The issue of borehole stability has attracted great attention worldwide but serious downhole problems still exist. The influences of various factors on borehole stability have been extensively studied in the literature. It is usually believed the lower limit of safe borehole pressure window is determined by collapse failure while the upper limit is determined by fracture failure of rocks. However, it is proved in this paper the upper limit can also be decided by collapse failure. A new model of determining the safe borehole pressure window is built and the new upper limit based on shear failure criteria is proposed, therefore, a more precise safe borehole pressure window can be determined. The effects of borehole orientation, structural weak planes, in-situ stress and pore pressure are then thoroughly analyzed. The results show that the two limits defined by shear failure criteria are resulted from principal stress alteration and usually featured by change of failure mode. The upper limit of shear failure criteria is quite critical in determining safe mud pressure under various conditions. The increase of mud pressure within boreholes may not alleviate collapse failures. The Mohr-Coulomb criterion confines a narrower window while the Drucker-Prager criterion predict a wider one. For determining the safe borehole pressure window, a uniform insitu stress and a low pore pressure will make it more necessary to consider the upper limit of shear failure criteria. The model built and conclusions drawn can provide new guidance for mud weight selection and well trajectory design in drilling practice.
查看更多>>摘要：Understanding the microscopic effects of supercritical CO2 (SC-CO2) on shale plays an essential role in carbon capture utilization and storage (CCUS). The variation of shale microstructures and micromechanical properties induced by SC-CO2 immersion is obscure, which is crucial in CO2-enhanced shale gas recovery. In this study, the organic matter (OM) and minerals of shale are identified in the microscale by scanning electron microscope (SEM), energy dispersive spectrometer (EDS), atom force microscope (AFM) and nanoindentation. The microstructures and micromechanical properties are measured before and after SC-CO2 exposure. The micro-mechanical properties variation of shale minerals and OM of shale are analyzed. The results show that the mechanical properties of OM have changed significantly after SC-CO2 exposure. Due to the interaction of CO2, the elastic modulus of OM increased by 124%. With the dissolution of CO2, the porosity of calcite increases from 7.1% to 8.1%, while decreasing by 6% in elastic modulus. By comparing the surface roughness calculated by AFM, the clay and OM swell. Although the mechanical properties are more discrete after CO2 immersion, the correlation between Young's modulus and hardness is better. These findings help understand the SC-CO2 exposure effects on shale and provide insights into the applications of SC-CO2 in unconventional resource development from a microscale perspective.
查看更多>>摘要：Tracer flowback testing has been proven as an efficient method to characterize hydraulic fractures and predict the performance of a hydraulically fractured well in a tight oil reservoir; however, few efforts have been made to characterize such fracture networks by quantifying tracer flowback behaviour due to the associated technical challenges. In this work, an efficient and effective numerical model based on the embedded discrete fracture model (EDFM) was developed, validated, and applied to characterize complex fracture networks and evaluate tracer flowback behaviour for a multistage fractured horizontal well. More specifically, such a model is applied to deal with complex fractures by dividing the fractures into segments using matrix grid boundaries and creating non-neighbouring connections (NNCs) using structured grids, while the complex fracture networks can be characterized by matching tracer flowback profiles with consideration of tracer dispersion and adsorption effects. Then, tracer flowback profiles for a fractured horizontal well with different fracture network patterns, including bi-wing fracture network (BWFN), opening-fissure fracture network (OFFN), fractal-like fracture network (FLFN), and mutually orthogonal fracture network (MOFN) are obtained. It should be noted that tracer flowback concentration (TFC) varies greatly with different fracture network patterns. Sensitivity analyses have been performed to examine the influence of different parameters (i.e., fracture width, fracture porosity, fracture conductivity, tracer adsorption, and tracer adsorption capacity) on the tracer flowback response for a fractured horizontal well with the BWFN and OFFN. It is found that the TFC increases as the fracture conductivity increases, while it decreases as the adsorption capacity increases. The higher the tracer dispersion coefficient is, the lower the tracer flowback peak concentration will be. Also, this model was validated and then extended to a field case, indicating the accuracy and efficiency of the newly proposed method to characterize the fracture networks compared with the microseismic events.
查看更多>>摘要：Hydrate flow assurance is critical to the exploitation of natural gas hydrate reservoirs. So far, hydrate formation and slurry flow behaviors in the presence of micron-sized sand particles are still unclear. Therefore, experiments of hydrate formation and slurry flow in the presence of micron-sized sand particles were performed in a high-pressure flow loop. The induction time and formation subcooling during hydrate formation process with micron-sized sand particles were studied, and cumulative formation probability under different formation sub-cooling with micron-sized sand particles was explored. Coupled with a semi-empirical hydrate formation kinetics model, hydrate formation kinetics parameters with micron-sized sand particles were calculated. The influence mechanism of micron-sized sand particles on hydrate formation was revealed. The calculation method for hy-drate slurry viscosity under conditions of constant volume fraction and variable shear rate was derived. Com-bined with viscosity of hydrate slurry with micron-sized sand particles, the importance of the fractal dimension to the accuracy of slurry viscosity prediction was emphasized. Considering hydraulic factors, collision between hydrates or micron-sized sand particles and pipe wall, and friction between hydrates or micron-sized sand particles and pipe wall, the calculation method of flow resistance coefficient of hydrate slurry with micron-sized sand particles was established.
查看更多>>摘要：The upper and lower limits and grading evaluation scheme of tight gas reservoirs (TGRs) at a microscopic pore structure level were explored by conducting high-pressure mercury intrusion porosimetry (HMIP), rate-controlled mercury intrusion porosimetry, nuclear magnetic resonance (NMR), and wettability experiments on tight rock samples from the Lower Cretaceous Shahezi (SHZ) Formation in the Xujiaweizi Rift, northern Songliao Basin. The results showed that the upper throat radius limit of the SHZ TGRs corresponds to 1.86 mu m, derived from the microscopic equilibrium state of buoyance and capillary forces. The above value is closely related to several geological factors, including a pore-to-throat radius ratio, the density difference between formation water and gas, formation dip angle, gas-water interfacial tension, and wettability. The SHZ Formation enters a tight reservoir stage when the burial depth is deeper than 3460 m. A new method integrating HMIP and NMR experiments was proposed to estimate the thickness of the adsorbed water film with a value of similar to 21.56 nm. The theoretical lower throat radius limit of the SHZ TGRs was determined as similar to 22 nm, considering the individual methane dimension. Natural gas can be scarcely injected into tight reservoirs below the theoretical lower limit, serving as theoretically invalid tight reservoirs in the study area. From the configuration relationship between pores and throats, two TGR types were identified in the SHZ Formation (types I and II). Type-I TGRs are char-acterized by relatively excellent seepage capacity, with the maximum connected throat radius and permeability of 0.4 mu m(-1).86 mu m and (0.015-0.27) x 10(-3) mu m(2), respectively, and their storage space mainly comprises abundant dissolution and residual intergranular pores. Furthermore, an adequate storage space (3.6% to more than 12%) and an appropriate burial depth (<5000 m) promote type-I TGRs to be the most favorable targets for current SHZ tight gas accumulation development in the Xujiaweizi Rift.
Larestani, AydinHemmati-Sarapardeh, AbdolhosseinNaseri, Ali
20页
查看更多>>摘要：No one can deny the ever-increasing importance of oil since it has influenced every aspect of humans' life. One of the most important pressure-volume-temperature (PVT) properties of crude oil, which is needed in a majority of production and reservoir engineering calculations, is the saturation pressure (bubble point pressure (P-b)). Having accurate knowledge about P-b is significant for both academia and industry. This communication concentrates on providing reliable experimental data from constant composition expansion (CCE) test as well as rigorous compositional models to predict saturation pressure of crude oils based on oil composition (H2S, N-2, CO2, C-1 to C7+), reservoir temperature, C7+ specifications (molecular weight and specific gravity). Seven advanced machine learning approaches, namely, decision trees (DTs), random forest (RF), extra trees (ETs), cascade-forward back propagation network (CFBPN), and generalized regression neural networks (GRNN) as well as multilayer perceptron (MLP) and radial basis function (RBF) neural networks were used for modeling. The CFBPN and MLP models were trained by three different training algorithms, namely scaled conjugate gradient (SCG), Bayesian regularization (BR), and Levenberg-Marquardt (LM). The modeling was done based on a databank consisting of 206 data points (130 points were previously published in the literature plus 76 points determined experimentally in this study). The results show that the DT model could provide the most reliable prediction with an average absolute percent relative error (AAPRE) of 4.43%. The efficiency of various equations of state (EoS) and empirical correlations were checked. According to the results, Peng-Robinson (PR) and the correlation developed by Elsharkawy were the most efficient EoS and empirical correlation with AAPRE values of 8.46% and 12.05%, respectively. Then, the sensitivity analysis revealed that the P-b was extremely affected by methane and C7+ mole percent. Finally, the Leverage approach confirmed the validity of the employed data, detecting only 7 points as outliers.
NSTL
Elsevier