CO2 enhanced gas recovery and sequestration in depleted gas reservoirs: A review

On the preferential flow patterns induced by transverse isotropy and non-Darcy flow in double porosity media

Integrated characterization of the fracture network in fractured shale gas Reservoirs—Stochastic fracture modeling, simulation and assisted history matching

To understand the influence of shear on the hydraulic properties of rock fractures, shear-flow tests were carried out on rock fractures with different surface roughnesses. Each rough-walled fracture was replicated in four specimens, which were sheared at different displacements under normal stresses that varied from 0.5 to 2.0 MPa. At each shear displacement, a series of hydraulic tests with different hydraulic gradients were performed, and the nonlinear flow regimes of the fluid within the fractures were investigated. The results show that Forchheimer’s law can well describe the nonlinear relationship between the flow rate and the hydraulic gradient in rough-walled fractures. Both the linear coefficient and nonlinear coefficient decrease during shearing but increase as the normal stress increases. The critical hydraulic gradient increases with an increase in the shear displacement and normal stress. With an increase in the joint roughness coefficient, the critical hydraulic gradient decreases. The normalized transmissivity exhibits a strong correlation with the Reynolds number. As the shear displacement increases, the fitted curves of the normalized transmissivity versus the Reynolds number shift upward but the curves shift downward with an increase in normal stress. Additionally, the Forchheimer coefficient decreases with an increase in the shear displacement but increases with an increase in the applied normal stress. Visualization tests show that the number of flow paths is large when the shear displacement is small due to various distributions of the contact areas and that the flow of dyed water over the entire fracture decreases. As the shear displacement increases, the flow resistance decreases due to the shear dilation-induced increase in the aperture, and the advantage channel flow is distinct in the fracture. The contact ratio rapidly decreases as the shear displacement increases from 1 to 3 mm and then slightly varies with a continuously increasing maximum shear displacement of 9 mm.

Experimental Study of the Nonlinear Flow Characteristics of Fluid in 3D Rough-Walled Fractures During Shear Process

This work is the first to employ and adapt the image-to-image translation concept based on conditional generative adversarial networks (cGAN) towards learning a forward and an inverse solution operator of partial differential equations (PDEs). Even though the proposed framework could be applied as a surrogate model for the solution of any PDEs, here we focus on steady-state solutions of coupled hydro-mechanical processes in heterogeneous porous media. Strongly heterogeneous material properties, which translate to the heterogeneity of coefficients of the PDEs and discontinuous features in the solutions, require specialized techniques for the forward and inverse solution of these problems. Additionally, parametrization of the spatially heterogeneous coefficients is excessively difficult by using standard reduced order modeling techniques. In this work, we overcome these challenges by employing the image-to-image translation concept to learn the forward and inverse solution operators and utilize a U-Net generator and a patch-based discriminator. Our results show that the proposed data-driven reduced order model has competitive predictive performance capabilities in accuracy and computational efficiency as well as training time requirements compared to state-of-the-art data-driven methods for both forward and inverse problems.

A framework for data-driven solution and parameter estimation of PDEs using conditional generative adversarial networks.

A comprehensive model combining Laplace-transform finite-difference and boundary-element method for the flow behavior of a two-zone system with discrete fracture network

Shale formation is featured in nanopores and much gas adsorptions. Gas flow in the shale matrix is not a singular viscous flow, but a combination of multiple mechanisms. Much work has been carried out to analyze apparent permeability of shale, but little attention has been paid to the effect of unique gas behavior in nanopores at high pressure and adsorbed layer on apparent permeability. This work presents a new model considering multiple transport mechanisms including viscous flow (without slip), slip flow, Knudsen diffusion, and surface diffusion in the adsorption layer. Pore diameter and mean free path of gas molecules are corrected by considering the adsorption layer and dense gas effect, respectively. Then the effects of desorption layer, surface diffusion, and gas behavior on gas apparent permeability in nanopores of shale are analyzed. The results show that surface diffusion is the dominant flow mechanism in pores with small diameter at low pressure and that the effect of adsorbed layer and dense gas on apparent permeability is strongly affected by pressure and pore diameter. From the analysis results, the permeability value calculated with the new apparent permeability model is lower than in the other model under high pressure and higher than in the other model under high pressure, so the gas production calculated using the new permeability model will be lower than using the other model at early stage and higher than using the other model at late stage.

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Apparent Permeability Model for Shale Gas Reservoirs Considering Multiple Transport Mechanisms

As one type of heavy oil reservoir with bottom water, a reservoir in Linpan oilfield features desirable physical properties and adequate energy in its bottom water. After exploitation of more than three decades, almost all wells have entered the high water cut stage. In view of the high water content situation among wells in this field and the bad effect of oilfield development, this thesis focuses on the investigation of remaining oil distribution of the reservoir. First, a fine three-dimensional geological model is established, including lithofacies model, porosity model, permeability model, and saturation model. On this basis, the corresponding numerical model is established and the historical fitting is completed. Finally, the main enrichment areas of remaining oil were determined from the aspects of water flooding characteristics, and the main controlling factors of remaining oil distribution and the main enrichment areas of the remaining oil were determined. The findings of the present study can contribute to the eventual formulation of potential-tapping countermeasures. Meanwhile, since heavy oil reservoirs with bottom water can be found prevalent in oil-producing areas both domestic and abroad, the proposals of this research are also helpful for exploitation of similar wells.

Fine 3-D Geology Modeling-Based Study of Remaining Oil Distribution in Linpan Oilfield

The low-permeability zones optimization can make the best use of low-permeability oil and gas resources. In this paper, ZZ zone, CYG zone in the periphery of Daqing oil field and YHW, BBC3, Z9 zone in Changqing oil field are selected respectively as the target zones, and then the method of gray target decision of multi-attribute with weight under the action of clout distance has been adopted to optimize the five zones and put them in order according to their qualities. For the purpose, main throat radius, mobile fluid percentage, start-up pressure gradient, the percent of clay contents, and crude oil viscosity are chosen as the evaluation indexes. Firstly, gray target decision matrix of multi-attribute aimed at the five target zones is developed, where transform operator of “rewarding superior and punishing inferior” is introduced to standardize the matrix, as a result, positive clout and negative clout of gray target model are obtained successfully. Then, the analytic hierarchy process is employed to obtain feature vector of the evaluation indexes’ judgment matrix, and by normalizing, the relative weights of the five evaluation indexes are calculated in the end. Next, based on the above process, positive and negative clout distance and comprehensive clout distance of target zones are calculated and applied to optimize the best zone. The smaller the comprehensive clout distance is, the better the zone is. The result shows that the best zone is BBC3 in Changqing oil field, while the rest are CYG, YHW, Z9, and ZZ zone. There is a satisfying match between assessment outcome and oil field practical development data, indicating it is effective and feasible to optimize low-permeability zones by means of gray target decision of multi-attribute with weight based on analytic hierarchy process.

Zones Optimization of Low-Permeability Reservoir Based on Multi-attribute of Gray Target Decision

Suizhong 36-1 oil field is located in Liaodong Bay of Bohai Sea. In the paper, residual oil content and distribution of target area is displayed and the ultimate goal is to study gas-polymer alternating injection and work out an appropriate injection scheme for it. First, gas-polymer alternating injection mechanism is demonstrated. Second, A and B platform’s fault upper area of phase I is selected as the target block to adopt gas-polymer alternating injection experiment. Third, the geological modeling for SZ36-1 oil field is established to describe sandstone distributing regularities in vertical and horizontal directions and further make it clear how residual oil distributes. Then, by the means of numerical simulation, history match is conducted. At last, through orthogonal design, the optimum injection program is determined successfully. With the help of orthogonal design, applying range analysis and variance analysis procedure, the optimum parameters of gas-polymer alternating injection are obtained from 16 forecast scenarios. They are as follows: the gas injection volume is 0.3 PV, the injection rate is 0.03 PV/a, the gas–liquid ratio is 1:2, and alternating injection cycle is 30 days. Furthermore, compared with polymer flooding, the oil recovery gas-polymer alternating injection increases by about 5%.

Guanyang Ding

Papers

A comprehensive model combining Laplace-transform finite-difference and boundary-element method for the flow behavior of a two-zone system with discrete fracture network

Apparent Permeability Model for Shale Gas Reservoirs Considering Multiple Transport Mechanisms

Fine 3-D Geology Modeling-Based Study of Remaining Oil Distribution in Linpan Oilfield

Zones Optimization of Low-Permeability Reservoir Based on Multi-attribute of Gray Target Decision

Study and Optimization of Gas-Polymer Alternating Injection Technique for Offshore Oil Field After Polymer Flooding