Multistage Acid-fracturing Increases the Dolomite Production in High Temperature Deep Horizontal Well

Abstract

The Sinian dolomite reservoirs in Southwest Oil and Gas Field, China, are characterized by HTHP, high stress, low porosity and permeability, large thickness, and presence of natural fractures and holes. Highly deviated well multistage acid fracturing can help expand the contacting area between wellbore and reservoir, thereby increasing the well production. Through experiments, acid fracturing simulations, staging optimization and field applications, some conclusions were obtained. Large-scale physical modelling experiments and numerical simulations show that, given the high horizontal stress difference, presence of natural fractures, can induce a complex fractures networks. The acid systems with different viscosities, such as self-generating acid, gelled acid and diverting acid, are optimized to, in conjunction with highrate injection and temporary diverting, improve the stimulated reservoir volume and conductivity of acid-fractures in the dolomite reservoirs. The combination of mechanical packers and sliding sleeves facilitate the effective isolation of HTHP dolomite reservoir. The positions of the sliding sleeves are designed according to the high-quality reservoir intervals determined by logging interpretation. The lateral of deviated well is 480m-970m long and stimulated by acid fracturing in 3-6 stages. The post-fracturing tracer testing proves the effectiveness of isolation. This technology was applied for 6 wells, with a daily gas production of (21–110) × 104m3/d after acid fracturing. It provides a new method to increase the production of highly deviated wells or horizontal wells in deep carbonate reservoirs.