Shale Formation Damage during Fracturing Fluid Imbibition and Flowback Process Considering Adsorbed Methane

Abstract

Hydraulic fracturing of shale gas reservoirs is characterized by large fracturing fluid consumption, long working cycle and low flowback efficiency. Huge amounts of fracturing fluid retained in shale reservoirs for a long time would definitely cause formation damage and reduce the gas production efficiency. In this work, a pressure decay method was conducted in order to measure the amount of fracturing fluid imbibition and sample permeability under the conditions of formation temperature, pressure and adsorbed methane in real time. Experimental results show that (1) the mass of imbibed fracturing fluid per unit mass of shale sample is 0.00021–0.00439 g/g considering the in-situ pressure, temperature and adsorbed methane. (2) The imbibition and flowback behavior of fracturing fluid are affected by the imbibition or flowback pressure difference, pore structure, pore surface properties, mechanical properties of shale and mineral contents. (3) 0.01 mD and 0.001 mD are the critical initial permeability of shales, which could be used to determine the relationship between the formation damage degree and the flowback pressure difference. This work is beneficial for a real experimental evaluation of shale formation damage induced by fracturing fluid.

Research and Applications of New Fracturing Technology in Low-Abundance and Greater-Depth Well LN-1 Reservoirs

“…The shale content of 22# in this well is 23.16% (among which, the illite/montmorillonite (I/S) formation is 36%), with weak to moderate water sensitivity and a pressure coefficient of 1.03, which is not conducive to fracturing fluid flow back. Therefore, the fracturing fluid system needs to be optimized to reduce fracturing fluid damage [30][31][32][33].…”

Salt Dissolution and Pore Structure Changes Induced by Fracturing Fluid in Shale Reservoirs

“…Hydraulic fracturing is an effective means for developing shale reservoirs. − However, during the process, a large amount of fracturing fluid is retained in the shale reservoir, − which can react with the rock. Under the influence of capillary forces and osmotic pressure, the fracturing fluid penetrates deeper into the shale reservoir, − and when it enters the shale matrix, it dissolves the salts in the pores.…”