A rock self-supporting high conductivity acid fracturing technique in a deep carbonate reservoir

Abstract

As carbonate reservoirs in deeper strata continue to develop, reservoir closure stress has significantly increased, where conventional acid fracturing technology cannot maintain acid-etched fracture conductivity and single well production rates are decreasing more quickly. This study proposes a rock self-supporting, highly conductive acid fracturing technique, where the shielding materials cover a portion of the primary hydraulic fracture surface to block the acid rock reaction. After acid injection, the unetched part will be a bearing surface, which serves as a large area and self-supporting high strength rock. This technique fundamentally changes the existing point support pattern of acid-etched fractures. Experimental results demonstrate that when the closed stress is <50 MPa, the self-supporting conductivity is 42% higher than the conventionally acid etched fractures. At 90 MPa closed stress, it can still maintain high support strength, which is more than eight times that of a conventional acid etched fracture. The equilibrium relationship between the fracture conductivity and rock support strength was determined using finite element stress simulation and fluid mechanics simulation. The results demonstrate that using a small cylindrical area, dislocation support, and multi-point support is conducive to the dispersion of high closure stress; moreover, the concentrated stress intensity of supporting rock can be reduced by 3–12 MPa. With decrease in supporting area, the stress intensity of the supporting rock is higher. Considering the compressive strength of the rock, the supporting area is >25%. When the rock is in the form of a dislocation support, the fluid disperses in the larger void channels, thus effectively maintaining fracture conductivity. The self-supporting acid fracturing technique is useful for increasing the utility of acid fracturing stimulation in deep and ultra-deep wells.