Theoretical understandings, key technologies and practices of tight conglomerate oilfield efficient development: A case study of the Mahu oilfield, Junggar Basin, NW China

摘要

A series of theoretical explorations and field tests have been carried out to efficiently develop the Mahu tight conglomerate oilfield in the Junggar Basin. Concepts of steered-by-edge fracturing and proactive fracturing interference were proposed. A series of innovative technologies were developed and implemented including optimization of 3-D staggered well pattern, proactive control and utilization of spatial stress field, and synergetic integration of multiple elements. Different from shale, the unique rock fabric and strong heterogeneities of tight conglomerate formation are favorable factors for forming complex fractures, small space well pattern can proactively control and make use of interwell interference to increase the complexity of fracture network, and the “optimum-size and distribution” hydraulic fracturing can be achieved through synergetic optimization. During pilot phase of this field, both depletion with hydraulically fractured vertical wells and volume fracturing in horizontal wells were tested after water injection through vertical wells, then the multi-stage fracturing with horizontal well was taken as the primary development technology. A series of engineering methods were tested, and key development parameters were evaluated such as well spacing, lateral length, fractures spacing, fracturing size, and fracturing operation process. According to geoengineering approach, the 100 m/150 m tridimensional tight-spacing staggered development method was established with systematic integration of big well clusters, multiple stacked pay zones, small well spacing, long lateral length, fine perforation clustering, zipper fracturing and factory operation. According to half-year production performance, 100 m/150 m small spacing wells outperformed 500 m/400 m/300 m spacing wells. Its average estimated ultimate recovery (EUR) of wells was identical with those best wells from large-spacing area. Compared with the overall performance of Mahu oilfield, the drainage efficiency and estimated recovery factor of this pilot were significantly boosted with improved economics.