One billion-ton super large oil field of Mahu is the largest oil and gas exploration achievement in China in recent years and has become the most realistic replacement area for increasing reserves and production in China as the world's largest conglomerate oil field till now. According to the complex reservoir-forming conditions in Mahu Sag, poor reservoir property, strong heterogeneity, and large sand body span, hydraulic fracturing in this area was facing serious challenges in fracture initiation and proppant placement. It has deepened the concept of volume fracturing technology and improved the effect of reconstruction; advanced chemicals to optimize replacement and reduce costs; tackled key perforation bridge plug with production technology to improve the level of operation according to 5 year’s stimulation experiences. The volume fracturing series technologies have been widely applied in 11 blocks and 97 wells in Mahu, including most of the exploration, evaluation, and development areas. For the tight conglomerate oil reservoir of Mahu, the fracturing and producing effects accompanied by economic development have been realized and effectively promoted, thus the average cumulative production increased by 37.5% per year.
The new Fish-bones Completion & Stimulation approach by needles in the pay stack aims at addressing heterogeneous tight carbonate by increasing flow area in the lower permeable streaks, which is efficient as hundreds of tunnels drain connecting the borewell to the body of the reservoir to increase well productivity and oil recovery. The initial plan includes selecting the best ones from Stair step horizontal well, Dual Lateral well, five lateral fish-bone drilling, and horizontal drilling along with hydraulic fracture. Considering the lessons of failure to clean internal tubes, the modified 4-1/2” Liner is installed in the lower two sub-layer by jetting subs combing with production subs for matrix acidizing in the upper one sub-layer as per modified Fish-bones Completion Design. In addition, special acid-releasing float shoes and new fishing baskets are applied to avoid those previous problems with this well technique. The candidate well shows good oil test and production, which improved by three times at 2000bbl/d with respect to the initial plan in the B field. This paper describes the technology background and characteristics, design factors, modified design, execution, well test, and lessons learned during implementation.
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