Research and Application of Complex Lithologic Fracturing Technology for Deep Well in High Temperature Gas Reservoir

Extremely high stress and high temperature remain the challenges of performing fracture stimulations in HPHT explorations. The chief lithology is basalt or volcaniclastic rock in Nanpu No.5 HPHT explorations structure. The reservoir depth is 4781.6 m ~ 5200 m, temperature is 170 ~ 180℃, permeability is 0.04 ~ 0.4 md. Early times, an exploration well was fractured which case size was 5.5in, closure stress was 61MPa and casing pressure was 70MPa, when displacement of pump was 2m3/min. Because of the extremely high pressure, the fracturing stimulation failed. In view of the difficulties of deep buried reservoir, high temperature, high Young's modulus and high fracturing pressure, we studied prefrac evaluation, high temperature acid, fracturing fluid, and related fracturing technology. Based on the analysis of rock and clay composition, X-ray diffraction, acid dissolution, lithomechanics and natural fractures experiments, it is believed that natural fractures are developed and the filling is mainly acid soluble minerals. Therefore, the technology of pre-acid + large-scale fracturing is developed. We developed a high-density fracturing fluid with super low guar gum concentration. The density of this fracturing fluid is 1.365 g/cm3 and can withstand temperature up to 175 ℃. And we also studied high temperature gelled acid resistance 170 ℃, perforation method, increasing fracturing equipment pressure-bearing capacity and multiple temporary plugging diversion technology. Based on the above technologies, it is refractured the failure well. It is successfully fractured. A total proppant volume is 60 m3 and the highest casing pressure is 74 MPa with a displacement of 5 m3/min. This technology was used in three wells of this block. The maximum total proppant volume is 125 m3 and the maximum casing pressure is 85 MPa in the well of NP5-i. The daily gas production of NP5-h after fracturing stimulation is 10.7 × 104m3 in the condition of Φ6.35 mm choke size.