Accurate sectional and differential acidizing technique to highly deviated and horizontal wells for low permeable Sinian Dengying formation in Sichuan Basin of China

Abstract

The Sinian Dengying formation reservoirs in Sichuan Basin of China have characteristics of high temperature, high pressure, deep buried depth, strong heterogeneity, low porosity and permeability, rich pore, natural fractures, vugs and high concentration H2S, CO2, which limit the reconstruction technologies about the gas reservoir. The formation poroperm of Tainei block Dengying unit is worse than that of Taiyuan block’s, and the difference of gas well productions in Tainei block is enormous. The technique of retarded acidizing with segmented by mechanical system was developed and applied in Dengying unit of Taiyuan block, which significantly raised the gas well production. It is difficult for the retarded acidizing technique to applied to gas wells in Tainei block, for the lower formation quality and immature fractures/vugs. The keys to formation reconstruction for highly deviated and horizontal wells are acid homogeneous placement and deep penetrating in order to connecting natural fracture and vugs system. With exploration and practice over several years, a set of segment acid fracturing comprehensive technologies for highly deviated and horizontal wells were formed, including accurate fragmenting based on quantizing evaluation of formation quality, differential acidizing of retarded acid and self-generation acid. The slow acid fracturing technology is used for the formation which the RES is over 1.0. Then, the multistage alternating injection acid fracturing technology is used for the formation which the RES is lower 1.0. The acid fracturing process parameters, such as displacement and acid strength, were optimized by experiments. The precision acidizing technique was applied for gas well of Tainei block Dengying unit, which the testing production of gas well is over 1 million cubic meter per day after aciding stimulated. The precision acidizing technique significantly raised gas well production of Tainei block Dengying unit and is helpful for exploratory development of Tainei block Dengying unit with low formation quality.