Research on the mechanism and process of fracture reduction for high stress reservoirs

Deep ultra-deep reservoirs are generally characterized by high rupture pressure and difficult to press open. The mechanical strength of the reservoir is attributed to the structural forces among rock mineral particles and the cementation between rock minerals. During the operation, chemical reactions occur when acid interacts with drilling fluids, filtrates, and acid - sensitive substances in the formation. This process not only efficiently removes contaminants within formation pores and expands the pore space but also damages the structure of rocks in the formation near the borehole. As a result, the mechanical properties of the rocks are weakened, and the fracture pressure of the reservoir is reduced. At the same time, it can destroy the rock structure in the formation near the borehole, weaken the mechanical properties of the rock, and reduce the fracture pressure of the reservoir, so that the subsequent acid pressurization construction can successfully open the formation. This paper carries out mechanical property degradation experiments on three kinds of cores with different mineral components, and characterizes the samples through XRD and SEM, specifically quantifies the effect of acid on the mechanics of different components of cores, and optimally selects the optimal degradation time. It furnishes practical technical instructions for field operations, breaking new ground in resolving two key issues. First, it provides effective solutions for the arduous task of initiating fractures in deep and ultra - deep reservoirs. Second, it introduces innovative strategies to manage the high wellhead pressures that occur during acid fracturing, thereby enhancing operational efficiency and safety.