Evaluation of Aqueous Phase Trapping in Shale Gas Reservoirs Based on Analytic Hierarchy Process

Abstract

A large amount of fracturing fluid retained in a shale gas reservoir that does not flow back after hydraulic fracturing could induce formation damage of aqueous phase trapping (APT). A shale gas reservoir generally has a multiscale pore and fracture structure, so both retained fracturing fluid distribution and gas transport have multiscale characteristics. In this work, a comprehensive evaluation method of shale APT damage based on the analytic hierarchy process in fuzzy mathematics is put forward considering the petrophysical properties and multiscale gas transport behavior in a shale reservoir. First, the critical indexes of shale APT damage evaluation are determined. Then the hierarchy structure for APT damage evaluation for a shale gas reservoir is constructed. Finally, the weights of the critical evaluation indexes of shale APT damage are calculated on the basis of the analytic hierarchy process. Taking Longmaxi shale reservoir as an example, the APT damage degrees for matrix and fractures are calculated to be 65% and 84%, respectively. The evaluation method for shale APT damage proposed in this work is beneficial to accurately predicting the productivity of a shale gas well and optimizing the hydraulic fracturing process to improve the stimulation effect.

Residual Damage, Its Consequences, and Remedial Measures on Post Hydrofrac Well Productivity: Learnt Lessons

“…This is due to suspended solids within the flowback fluid. The shale reservoir pressure usually decreases with more water phase flowback, thus, leading to gas absorption in the shale matrix pore wall as it diffuses into micro-fractures [124]. As a result, gas saturation in the fractures increases with the continuous increase in the permeability of the gas phase and the constant decrease of the water phase permeability.…”

“…However, a significant decrease in the adhesion strength of those solids retained in micro-fractures leads to the migration of fine particles in the reservoir. The gas flows to the surface as water phases in the retained fracturing fluid gradually evaporate during the later flowback stage, thus, driving soluble salts in the liquid phase to seed out [124]. Therefore, not only fine migration and water phase trapping but the solid-phase residual blockage resulting from salt precipitation needs to be taken care of to optimize the flowback procedures in case of high-mineralization of flowback fluids [125].…”

Virtual Special Issue of Recent Research Advances in China: Unconventional Gas

“…The second review by Zhang and Cheng is a mini review on the technical aspects of sample preparation and data analysis using small-angle neutron scattering (SANS) and ultrasmall-angle neutron scattering (USANS) for shale samples. The original research articles cover a wide spectrum of research on shale gas, including reservoir characteristics, ,,, reservoir modeling, ,,, exploration, equipment-related, ,, gas transport properties, ,,,, shale property characterization, , gas adsorption, ,, gas generation, produced water treatment, , methane conversion, etc.…”

Effects of Microscopic Pore Structures on the Spontaneous Imbibition of Longmaxi Shale

“…Shale gas has aroused great attention in recent decades due to global energy shortage. , China is reported to have a significant amount of shale resources in Sichuan, Junggar, Ordos, and Tarim Basins. , Hydraulic fracturing combined with horizontal drilling remains to be the key technique for unlocking these shale resources in China. − Thousands of tons of fracturing fluids are pumped into these shale gas wells to initiate the flow pathways during the fracturing treatment. However, a limited portion of these fracturing fluids can be recovered after the fracturing treatment. , The distribution of unrecovered fracturing fluids remains unclear.…”