Abstract
The unconventional reservoir in Mahu Basin in Xinjiang Oilfield has more than one billion tons of oil and gas resources, and it is the first effectively developed glutenite reservoir in China. In the development of this basin, we faced with the following problems: complex lithology (glutenite reservoir), large reservoir depth (3750-3900m), low permeability (average porosity 9.8%, permeability 5.4mD), thickness variation (3.4-23m), multiple thin layers distribution (3-5 thin layer distribution) and high-pressure coefficient (1.6-1.8). This kind of reservoirs have no economical production without hydraulic fracturing, while the stimulation operation still faced with difficulties such as un-predicate fracture propagation, high cost and multi-layers. In order to solve the above problems, we investigated the economic stimulation of glutenite formation: (1) 30cm×30cm×5cm rock sample experiments revealed fracture initiation and expansion regulation including piercing gravel, bypass gravel and stop expansion; (2) A low concentration fracturing fluid system was developed, guar concentration reduced from 0.40% to 0.25%. Viscosity of this kind fracturing fluid can maintain 100mPa.s under condition of 90°C and 170S-1 after 120min. By using this fracturing fluid, operation cost can be reduced by 5.8$/m3, residue can be reduced by 10%. (3) Optimize the p'n'p technology of staged fracturing for horizontal wells, establish an effective fluids pump process, that is, pre-gel to initial fractures, followed slickwater to extend fractures then followed gel to carry sands. (4) A soluble plug and multi-stage cementing sleeve was formed after the investigation of fracturing completion tools. (5) Replacement of ceramsite by low-cost quartz sand, reduced 31 million US dollars in 72 horizontal wells. (6) A factory-fracturing model has formed in which operating time can be reduced by 20%. The above integrated technology has been applied in more than 135 wells, the daily oil production per well has increased from 5t/day to 26.7t/day and now the basin has a capacity of 2.32 million tons. Application of the integrated technology can be references for efficiency development of low permeability glutenite reservoirs.
