A New Acid Fracturing Fluid System for High Temperature Deep Well Carbonate Reservoir

Abstract

When a high temperature deep well carbonate reservoir is stimulated with conventional acid fluid, some unfavorable behaviors often occur, such as high acid-rock reaction rate, short effective reaction distance of live acid, failure of acid etching in the acid fracture front, and serious corrosion to downhole string. This paper presents a new acid fracturing fluid system. This system consists of the acid-generator SGA-E, the optimized polymeric thickener CHJ-1 and the cross-linking agent SJL-1. With the performance of water-based fracturing fluid, this system can be used as prepad during acid fracturing. Moreover, this system has weak or no acidity at low temperature and slow release of H+at high temperature (120-150°C) in fractures, Its ultimate effective acid concentration is about 8% which is capable of effective acid etching. During pumping, this system shows less corrosion to the string, so few corrosion inhibitor is required. This new acid fracturing fluid system can achieve effective acid etching of a whole fracture, so as to increase the stimulated reservoir volume.

Self-Generated Organic Acid System for Acid Fracturing in an Ultrahigh-Temperature Carbonate Reservoir

“…In order to solve the shortcomings of conventional acidizing, a retarded acid system has been used on a large scale, including self-generated acid. − The self-generated acid system has no obvious strong acid characteristics on the ground and is a neutral or weak acid. The self-generated acid system is composed of an acidogenic acid mother liquor and does not contain hydrochloric acid, which effectively solves the problem of pipeline corrosion. , After the self-generating acid mother liquor is injected into the formation, it can slowly release the acid through the reaction, which greatly delays the acid–rock reaction rate and increases the penetration distance. , The existing types of self-generated acid mainly include halogenated hydrocarbons, formaldehyde, halogen salts, fluoroboric acid or fluoride containing salts, acyl halides, complex acids, etc. , The concept of self-generating acid proposed by Templeton for the first time is based on HCOOHCH 3 and NH 4 F as the main components of the acid system. HCOOCH 3 is hydrolyzed to produce H + , and NH 4 F hydrolysis produces F – ; then HF is formed for acidizing the sandstone reservoir.…”

“…The self-generated acid system is composed of an acidogenic acid mother liquor and does not contain hydrochloric acid, which effectively solves the problem of pipeline corrosion. 18 , 19 After the self-generating acid mother liquor is injected into the formation, it can slowly release the acid through the reaction, which greatly delays the acid–rock reaction rate and increases the penetration distance. 20 , 21 The existing types of self-generated acid mainly include halogenated hydrocarbons, formaldehyde, halogen salts, fluoroboric acid or fluoride containing salts, acyl halides, complex acids, etc.…”

“…Subsequently, a large number of scholars have studied the self-generating acidizing of carbonate rocks. Gao et al 19 used the acid-producing agent SGA-E to form an acid system for carbonate reservoir wells at 120–150 °C. The system slowly produces acid above 100 °C, and the final acid concentration is equivalent to 8% hydrochloric acid, which can be applied to carbonate acidizing above 100 °C.…”