Study on Matrix Damage and Control Methods of Fracturing Fluid on Tight Sandstone Gas Reservoirs.

Abstract

Hydraulic fracturing is a highly effective method for stimulating the development of gas reservoirs. However, the process of pumping fracturing fluid (FF) into the reservoir unavoidably causes damage to the surrounding matrix, leading to a decrease in the overall stimulation effect. To assess the extent of matrix permeability damage caused by the intrusion of FF, as well as its impact on the pore throat structure, and to propose appropriate measures to control this damage, we conducted a series of experimental studies on tight gas reservoirs. These studies included mercury intrusion, core flow, nitrogen adsorption, linear expansion, and contact angle measurements. The findings revealed that the damage inflicted on matrix permeability by FF was significantly greater than that caused by its gel-breaking counterpart. Surprisingly, the damage rate of the rejecting fluid to the matrix was found to be comparable to that of its gel-breaking counterpart. The fractal dimension (D2) was observed to have a strong correlation with surface area, pore volume, and mean pore size, making it an effective means of characterizing pore structure characteristics. After the rock samples were displaced by the formation water, the D2 value decreased, leading to a decrease in the complexity of the pore throat structure and an increase in matrix permeability. Conversely, the displacement of the FF increased the D2 value, indicating a gradual complication of the pore throat structure and a more uneven distribution of pore sizes. The inclusion of polyamide in antiexpansion FF, as well as its gel-breaking counterpart, proved to be effective in inhibiting the hydration and expansion of clay minerals, thereby reducing water-sensitive damage. Additionally, the use of surfactants with low surface tension enhanced the flowback rate of FF by increasing the contact angle and reducing the work of adhesion. This, in turn, helped to decrease the apparent water film thickness and expand gas flow channels, ultimately improving gas permeability.