Success Story of Production Improvement in a Matured Carbonate Reservoir in Bahrain Field Using Radial Drilling Technology

Abstract

Abstract The Mauddud reservoir discovered in 1932 in Bahrain is now in a mature stage of development with declining production. Conventional acid stimulation to improve production in Mauddud reservoir is fraught with uncertainty due to poor cement bond behind casing resulting high gas production from overlying large gas cap. With proliferation of new and old technologies, the recent upsurge in oil prices are enabling operators to capitalize on new opportunities. This paper discusses the radial drilling technology, well selection criteria, productivity calculation methodology using analytical models and successful field application on two wells in Mauddud reservoir. The objective is to improve oil production economically from existing low productivity wells en route to increase ultimate recovery. Radial drilling is implemented in two zones of Mauddud reservoir with two laterals in each zone having a length of ± 100 ft. for each lateral. The process generally involves running a milling tool downhole using a modified coil tubing system to a target depth to mill away the casing, followed by a jetting tool that uses high-pressure fluids combined with hydraulic impact forces to penetrate the reservoir rock. This is achieved by utilizing the jetting forces and covert it to forward and rearward forces to make small diameter horizontal boreholes of approximately 0.066 ft. to 0.164 ft., and lengths up to 300 ft. using high-pressure water jets. A detailed workflow and selection criteria are prepared to select the candidates for radial drilling. Detailed geological, production and reservoir engineering prognosis are carried out to reduce the risk and optimize its application. Production improvement is estimated using both conventional horizontal and multilateral analytical well models to evaluate its application. The results showed significant improvement in well productivity as compared to historical production without radial drilling and reduction in water cut in one well. The post-drilling initial production test data shows +300% gain in oil rate in one well. The second well exhibits +90% increase in initial oil rate. The economics are evaluated based on base case and improved oil rates using decline curve analysis, which look promising. Emboldened by the success of the radial drilling, this technology is being considered to be implemented in similar wells across Mauddud reservoir. Radial jet drilling is a fit-for-purpose, cost-efficient technology to improve production in Mauddud reservoir overlain by gas cap by bypassing damaged zones in the vicinity of the borehole. Besides accessing untapped sweet spots, both old and new wells with low productivity and/or where production has declined are amenable to stimulation using this technology. The radial drilling is a cost-effective and proven technology to enhance production in a matured reservoir. The technology is ideally suitable to drain larger areas for thin oil pay/s overlain by thick expanding gas cap.