Conventional mud acid (a mixture of HF and HCl) is the most commonly used acid system for the stimulation ofsandstone formations. However, well known disadvantages such as fast reaction rate, precipitation and matrix de-consolidation restrict the usefulness of this type of acid.A high-temperature deep-penetrating acid system (HTDP acid) is presented in this paper. Compared with regular mudacid, the HTDP acid penetrates deeper into the formation by generating HF at a slower rate in situ. HTDP acid is one type ofretarded mud acid, and it is made up of composite phosphate and fluoride salt. A new corrosion inhibitor has been developedwhich makes HTDP acid suitable for formations with temperatures as high as 356℉. Very important, the HTDP acid hasmuch higher quartz solubility compared with the mud acid and could reduce precipitation.The HTDP acid has been used in 23 wells in China offshore oilfields since 2006, and 22 of the stimulation jobs havebeen deemed effective. Among those wells, five are high temperature/low permeability wells (the highest temperature is 293℉) and are located in China's Bohai Bay. Two of the wells are in a loose sandstone formation in the South China Sea. Theproduction of these wells after stimulation was enhanced remarkably.Though developed and used in China, the acid together with the high temperature inhibitor could be extrapolated toother similar sandstone reservoirs world-wide.
展开▼
