Experimental investigation on the hydraulic fracture initiation and propagation of temporary plugging and acid fracturing in a large-scale true triaxle simulation

Abstract

The study investigates the initiation and propagation of multi-fractures during temporary plugging and diverting acid fracturing in deep carbonate reservoir rocks with tight formations. An orthogonal experiment using prepared carbonate outcrop rock mass simulated a genuine triaxle scenario for temporary plugging multi-fracture network acid fracturing. Analysis of 3D section scans revealed the roughness of fractured surfaces caused by acidization, helping understand the effects of different types and amounts of temporary plugging agents combined with changes in acid injection displacement on initiation process and morphological complexity during propagation when forming these temporarily plugged fractures. Design parameters for temporary plugging acid fracturing were optimized based on criteria such as fracture pressure, transformed area, and pre- and post-plug acid fracturing transformation indexes. The concentration of the temporary plug agent affects the pressure-bearing capacity of the plug layer, but excessive pumping or rapid compression can damage fibers. Rigid particle plugs allow for quicker steering, while flexible particle plugs enable slower steering. The turning and propagation of acid fracturing fractures show unsteady behavior. The sensitivity factors affecting temporary plugging acid fracturing are ranked as follows: type of temporary plugging agent > acid injection displacement > dosage of temporary plugging agent. For optimal design parameters in a temporary plugging acid fracturing process, it is recommended to use H-type particle temporary plugging agent at a dosage of 10 g and an acid injection displacement rate of 400 mL/min. Increasing both the concentration and pumping displacement rate can enhance its steering ability; however, incorporating fibers and particles into the mixture is advisable to improve stability within the plugged layer as well as throughout acid fractures.