No-Damage Stimulation By Use of Residual-Free Diverting Fluids

Abstract

This article, written by Special Publications Editor Adam Wilson, contains highlights of paper SPE 177495, “No-Damage Stimulation Based on Residual-Free Diverting Fluid for Carbonate Reservoir,” by Y. Shi, X. Yang, F. Zhou, Y. Gao, S. Lian, X. Li, and X. Han, Research Institute of Petroleum Exploration and Development, CNPC, prepared for the 2015 Abu Dhabi International Petroleum Exhibition and Conference, Abu Dhabi, 9–12 November. The paper has not been peer reviewed. Horizontal wells and acid stimulation are essential technologies for the development of complex carbonate reservoirs. However, conducting effective stimulation in horizontal wells with long intervals is extremely difficult because traditional acid systems can flow only into the high-permeability formations, leaving the damaged formation untreated. This paper studied three residual-free fluid systems for acid treatments and fracturing in order to develop no-damage or reduced-damage and highly effective stimulation techniques for long-interval wells. Introduction Horizontal wells are essential for the development of carbonate reservoirs in China. However, horizontal wells always have long intervals, so they are extremely difficult to stimulate. The fluid systems used are a critical aspect of high-efficiency stimulation. Traditional acid systems, which do not have diverting capabilities, can flow only into the high-permeability formations, leaving the damaged formation untreated. That is why long-interval wells with high heterogeneity need to be treated by a diverting acid system. A new diverting acid system should have the following characteristics: The capability to reduce the acid/rock reaction rate; a diverting performance to achieve uniform stimulation in a carbonate reservoir with high heterogeneity; and use of clean chemical additives to eliminate or limit damage. This paper analyzes three clean fluid systems for acid treatment and fracturing. The no-damage stimulation systems considered are a temperature-controlled deep-diverting acid system (TCA), a pH-controlled self-diverting acid system (DCA), and a fracture-reorientation technology using degradable fiber (RDF). TCA Diverting Mechanism of TCA. The TCA system is similar to ordinary gelled acid during pumping. The gelling agent can dissolve in water in a short time, reducing the frictional resistance of the system dramatically and making it easy to prepare and pump. At formation temperature, the system has a high viscosity to ensure diverting and retarding performance. After the acid fracturing treatment, the viscosity of the spent acid decreases in order to flow back easily and leave no damage in the formation.