Next Generation Acid System — Deep-Penetrating Non-Corrosive Fluid for High Temperature Sandstone Stimulation

Abstract

In high-temperature sandstone reservoirs especially at temperatures above 450°F, the rapid reaction of the acid treatment fluid and the secondary/tertiary reactions with the clays lead to formation damage. Moreover, at these high temperatures, the HCl/HF based acid systems are extremely corrosive to the wellbore tubers and downhole equipment's. This paper presents the next generation acid system that utilizes non-corrosive fluids to generate HF acid for high temperature sandstone stimulation. The non-corrosive deep-penetrating acid is a neutral, non-reactive treatment fluid at the surface and only when it is injected in the formation, it generates HF at a controlled rate in situ under temperature and time. The in-situ generated HF at a controlled rate allows for deep penetration of the acid in the formation. A series of solubility testing in HPHT reactor was first conducted to understand the chemical reactions that generate the acid as a function of temperature, concentration of acid generating components, and time, and to identify the optimum composition that maximize the dissolving of quartz and minimize the potential precipitation from reaction with clay minerals. Coreflow testing was then conducted at 475°F using 1.5″ in diameter and 6″ in length Berea sandstone cores to evaluate the performance of the new acid system for sandstone stimulation. Solubility testing showed that the new acid system has high dissolving power for calcite and silica and potential to minimize precipitations when reacted with clays. In Coreflow testing, the non-corrosive deep penetrating acid is effective to stimulate sandstone and provides remarkable permeability improvement by at least 60% at 475°F. Because of the in-situ controlled generation of HF, it penetrates deeper in the formation and minimizes the potential for precipitations. The non-corrosive deep-penetrating fluid system provides the industry with an effective solution to deeply stimulate sandstone reservoirs unlocking the full potential especially at temperatures above 450°F, and a safe non-corrosive fluid for wellbore tubulars and equipment. Moreover, the new fluid technology would eliminate the need for acid tanks on site, reduce transportation difficulties, and eliminates HSE concerns and acid exposure to personnel in the field.