Understanding Shale Gas Production Mechanisms Through Reservoir Simulation

Abstract

Shale gas has changed the energy equation around the world, and its impact has been especially profound in the United States. It is now generally agreed that the fabric of shale systems comprise primarily of organic matter, inorganic material and natural fractures. However, the underlying flow mechanisms through these multi-porosity, multi-permeability systems are poorly understood. For instance, debate still exists about the predominant transport mechanism (diffusion, convection and desorption) as well as the flow interactions between organic matter, inorganic matter and fractures. Furthermore balancing the computational burden of precisely modeling the gas transport through the pores versus running full reservoir scale simulation is also contested. To that end, commercial reservoir simulators are developing new shale gas options but some, for expediency, rely on simplification of existing data structures and/or flow mechanisms. We present here the development of a comprehensive multi-mechanistic (desorption, diffusion and convection) multi-porosity (organic materials, inorganic materials and fractures), multi-permeability model that uses experimentally determined shale organic and inorganic material properties to predict shale gas reservoir performance. Our multi-mechanistic model takes into account gas transport due to both pressure-driven convection and concentration-driven diffusion. The model accounts for all the important processes occurring in shale systems, including desorption of multi-component gas from the organics surface, multi-mechanistic organic-inorganic material mass transfer, multi-mechanistic inorganic material-fracture network mass transfer, and production from a hydraulically fractured wellbore. Our results show that Dual-porosity Dual-permeability (DPDP) with Knudsen diffusion is generally adequate to model shale gas reservoir production. By comparing Triple-porosity Dual-permeability (TPDP), DPDP and Single-porosity Single-permeability (SPSP) formulations under similar conditions, we show that Knudsen diffusion is a key mechanism and should not be ignored. We also guide the fractures design by analyzing flow rate limiting steps. This work provides a basis for long-term shale gas production analysis and also helps define value-adding laboratory measurements.

A fully coupled multiscale shale deformation-gas transport model for the evaluation of shale gas extraction

“…Many scholars adopt the continuum mechanics model to investigate the gas flow within shale reservoirs. Specifically, both the single porosity single permeability model [1] and dual porosity dual permeability model [2][3][4][5] are used to represent the gas flow within the shale matrix. For the single porosity model, it is assumed that the porous medium is made up of uniform pores with the same properties, which ignores the differences between big cracks and small pores.…”

Well Performance Simulation and Parametric Study for Different Refracturing Scenarios in Shale Reservoir

“…where Q gwell is the production rate of the fracture system and can be defined based on the Peaceman model [26]:…”

Characterization methods for mass transfer of multiple media in shale gas reservoirs

“…级左右 [11,12,42,43] , 需要采用双渗介质模型 [43] . 考虑页岩 气藏发育干酪根有机质、无机基岩以及压裂改造产生 的次生裂缝网络等多尺度介质, 学者们 [15,44~46] 引入多 重连续性模型描述页岩气藏多尺度介质耦合运移机 制, 多重介质之间流体跨尺度传质多采用拟稳态窜流 表征 [17,47,48] , 其合理性需要进一步研究讨论. 离散裂缝 模型(DFM)是在裂缝分布规律定量认识的基础上, 采 用非结构化网格等手段表征次生裂缝几何形状和位 置, 通过有限元等数值方法求解基质-裂缝耦合渗流规 律 [49~52] .…”