Study on a Novel Comprehensive Numerical Simulation Model of Self-Generating Acid Fracturing for Ultra-Deep Carbonate Reservoir in the Shunbei Oilfield

Abstract

Summary China's continental marine carbonate rocks are rich in oil and gas resources, but the reservoir conditions are poor. Acid fracturing is the main technological measure for the stimulation of carbonate reservoirs at home and abroad. Due to the high temperature of carbonate reservoirs in China, the acid-rock reaction speed of gelled acid and other commonly used acid systems in the field is fast, so that the effective distance of acid is short (50-70m), the acid etched fracture conductivity at the distal end of the fracture is low, and the deep penetration transformation cannot be realized, which has a great influence on the stimulation effect of the reservoir. In this paper, a numerical model that can accurately describe the whole process of self-generating acid reaction under in-situ conditions is established. At the same time, fracture propagation, flow field, temperature field, concentration field and reaction process are coupled. The simulation analysis of self-generating acid concentration distribution, etching characteristics and effective acid etching fracture length under different influencing factors is carried out to understand the self-generating acid, etching law and main control factors, which provides a basis for the optimization design of self-generating acid fracturing process. The results show that (1) Temperature is the main factor affecting the acid generation rate of self-generating acid. The effective acid etching length at the distal end increases with the increase of temperature, the effective acid etching length at the proximal end decreases with the increase of temperature, and the overall effective acid etching length increases. Under the condition of 10 mD permeability, high displacement plays a role in promoting the effective acid etching fracture length, (2)The higher the matrix permeability, the smaller the effective acid etching fracture length.(3)Under the condition of small acid amount (300 m3) and medium acid amount (500 m3), the displacement has little effect on the effective etching fracture length. Under the condition of large acid amount (800 m3), the displacement has a certain promoting effect on the distal effective etching fracture length. (4)The greater the amount of acid injection, the greater the distal effective acid etching fracture length.