Deep Penetrating Acid Fracturing Involving Self-Generated Acid in Carbonate Reservoirs of the Tahe Oilfield

Reservoir conditions are deteriorating as carbonate reservoir exploration and development blocks of the Tahe Oilfield extend to the periphery of the oilfield. Under such circumstances, it is necessary to improve productivity through acid fracturing. Higher acid-rock reaction velocities of conventional acid fluids under high temperature, and large filtration losses would significantly affect penetration performances of acids. To solve this problem, a temperature-resistant self-generated acid system was developed to generate acids under high temperature with lower reaction velocity. It consists of highly polymerized carbonyl compound (agent A) and ammonium salt (agent B). Experimental results showed that the largest acid volume can be generated when agent A and B volume are equal; the self-generated acid has lower acid-rock reaction velocity and better acid fracture conductivity. In addition, it is highly compatible with formation water and the common acid system used in the Tahe Oilfield. This self-generated acid system has been used in 15 wells in the Tahe Oilfield. The production in the primary production period after acidizing was 1.5 to 2.5 times of that of adjacent wells (without self-generated acid fracturing). The results showed that the deep penetration acid fracturing of the self-generated acid can meet the requirement for deep penetration stimulation of carbonate reservoirs in the Tahe Oilfield.