Optimal design on the stereoscopic layout of acid system in strong-heterogeneity thick sandstone reservoirs

The reservoir of Jidike Formation in the TZ Gas Field is characterized by great thickness, moderate porosity, moderate-low permeability and non-uniformly developed natural fracture. The reservoir damages caused by the invasion of drilling mud mainly include the “non-linear” damage induced by strong reservoir heterogeneity and the “non-radial” damage induced by natural fractures, and led to greater difficulty in blockage removing. The acid system was selected based on experimental studies, the critical displacement to open natural fractures was determined by means of the natural fracture opening discrimination model, and the blockage removing effects of network-fracture acidizing in fractured reservoirs were experimentally evaluated. Based on the research results, combined with the concepts of combined uniform acid distribution and network-fracture acidizing process, the optimal stereoscopic acid layout method was developed, the self-diverting mud acid of 13.5%HCl+1%HF+4% diverting agent was selected for uniform acid distribution, the mud acid of 13.5%HCl+1%HF was selected for in-depth acidizing, and the minimum displacement of network-fracture acidizing was optimized to be 3 m³/min. The proposed optimization method was applied on site in Well TZ-C-X2. The acidizing effect is remarkable with the total skin factor dropping from 15.43 to 0.09 after the acidizing. The research results provide the technical support for the design of efficient acidizing in thick heterogeneous sandstones.