Pre-acid system for improving the hydraulic fracturing effect in low-permeability tight gas reservoir

Nianyin Li,Fei Chen,Jia Kang,Peihong Han,Jiajie Yu

doi:10.1007/s13202-021-01129-x

Abstract

Hydraulic fracturing is an important technical means to improve the development effect of low-permeability oil and gas reservoirs. However, for low pressure, low-permeability, tight, and high-clay sandstone gas reservoirs, conventional propped fracturing can cause serious damage to the reservoir and restrict the fracturing effect. The pre-acid fracturing technology combines acid treatment technology with sand-fracturing technology. A pre-acid system that meets special performance requirements is injected before fracturing. The pre-acid reduces the formation fracture pressure and removes clay damage. During acid flowback, the fracturing fluid is promoted to break the gel, dissolve the fracturing fluid residue and polymer filter cake, clean the supporting cracks, and effectively improve the fracturing effect. This study analyzes the process principle and technical advantages of the pre-acid fracturing technology based on the laboratory evaluation of the fracturing damage mechanism of low-permeability tight gas reservoirs. To meet the performance requirements of low-permeability tight gas reservoirs and pre-acid fracturing technology, a set of polyhydrogen acid system with long-lasting slow reactivity, low damage, and low corrosion was developed and used as the pre-fracturing acid. The acid system is mainly composed of the main agent SA601 and the auxiliary agent SA701. Then, on the basis of laboratory experiments, this acid system is used as the fracturing pre-acid to evaluate the fracturing improvement effect. The results show that the fracturing fluid system can better dissolve the fracturing fluid filter cake and remove the fracturing fluid damage.

Highlights

For a long time, hydraulic propped fracturing has become an important technical measure for increasing the production of low porosity and permeability oil and gas reservoirs (Holditch 1979; Gdanski and Fulton 2006)
To further improve the fracturing effect and fracturing efficiency, it is necessary to redefine the idea of deep reconstruction of low-permeability tight gas reservoirs, integrate the advantages of acidification into the fracturing process, and consider the acidification in high fracture pressure, tight sandstone reservoirs, and sensitive sandstones
Based on the characteristics of low-permeability tight gas reservoirs and the performance requirements of the preacid fracturing process for the pre-acid system, a new type of chelating acid system—polyhydroacid is developed as the pre-acid

Summary

Introduction

Hydraulic propped fracturing has become an important technical measure for increasing the production of low porosity and permeability oil and gas reservoirs (Holditch 1979; Gdanski and Fulton 2006). When fluid flows back into the well, fracturing fluid flows back first, followed by residual acid It can make full use of the degradation and cleaning effects of low pH residual acid, promote the gel breaking of fracturing fluid, dissolve the fracturing fluid filter cake, clean support fractures and improve the conductivity of support fractures (Jiang et al 2015). This process combines acid treatment technology with sand-fracturing technology, which can play the advantages of conventional fracturing to reform the reservoir, and significantly solve its existing problems and improve the fracturing effect (Qasem et al 2007). The mechanism of the pre-acid in improving the fracturing effect was evaluated in terms of the pre-acid reducing rock fracture pressure, promoting fracturing fluid gel breaking, reducing clay damage, cleaning the matrix, and supporting cracks

Methods

Results

Conclusion