Successful Application of Stimulation Strategies for Low-Pressure Natural Fractured Carbonate Oil Reservoir

摘要

Successful stimulation requires creating a long,rnconductive fracture in low pressure, low permeability, naturalrnfractured carbonate reservoir, which results in connecting veryrnlarge surface areas of the formation with an extremelyrncomplex fracture network. Stimulation has been faced lots ofrnchallenges, including the potential of fracture tortuosity, prematurernscreen-out, severe treatment fluid leakoff and therndifficult flow backup of the frac fluid because of low pressure.rnExtensive laboratory study was conducted to optimizernstimulation for low-permeability carbonate reservoir. Acidrnrock reaction experiments using gelled acid and emulsifiedrnacid were accomplished to get full understanding the kineticsrnof acid reaction with carbonates. Fracture conductivityrnexperiments were conducted with a unique conductivityrninstrument using limestone samples designed to simulaternvarious acid fracturing and propped fracturing process. Thernfindings from conductivity tests clearly demonstrated that arncombined technology of propped fracturing and acidrnfracturing can be used to maximize fracture conductivity.rnBased on the experimental results and plentiful fieldrnpractices, the following stimulation modes are established andrnoptimized: propped fracturing, multistage acid-fracturing withrnclosed fracture acidizing (CFA), pad acid fracturing, selectivernacid fracturing and diverting acidizing for heterogeneousrnformations. Also presented are two clean-up approaches:rnnitrogen gas lift technology with coil tubing and multistagerngas-lift-valve technology to help spent acid flowback.rnFor the past 5 years, more than 100 treatments have been donernand indicated that 85% of them were successful and effective,rnwith average single-well oil increment of 20t/d and service lifernof over 500 days. Long-term production performance in stimulated wells proved the successful strategies ofrnstimulation and developed a comprehensive treatmentrntechnology suitable for low pressure, low permeability, andrnnatural fractured carbonate reservoirs.