Volume fracturing technology based on geo-engineering integration for ultra-high temperature and ultra-deep heterogeneous carbonate reservoir

There are abundant oil-gas resources in Ordovician buried-hill carbonate reservoirs of the northern Jizhong depression. Due to complex lithology (mixed with dolomite and limestone), ultra-high temperature (180℃)and high stress gradient (0.023 MPa/m), various technologies have been used previously, but no breakthrough was achieved. Aiming at the above reservoir geological problem, reservoir evaluation, process optimization, technique design and other research were carried out on basis of reservoir geological characteristics, so as to form the special volume fracturing technology of geo-engineering integration for ultra-high temperature and ultra-deep heterogeneous carbonate reservoir. Firstly, the geological and engineering volume fracturing factor scheme of complex fissure network was validated by the physical test of 1 m3 huge rocks and numerical simulation means in combination with geological characteristics, and the results show that even if the reservoir is mainly characterized by micro fissures, poor connection and high dual-direction stress deviation (7.0-9.8 MPa), complex fissure network hydraulic fractures can also be achieved by high displacement-high-low viscosity liquid combination, temporary plugging diversion and other techniques. Secondly, the integrated volume fracturing technology was applied for ultra-high temperature and ultra-deep reservoir, i.e., through the safety and mechanical check on tubular column, volume fracturing pressure prediction and impact analysis on measuring-pilot production, the previous multi-processes were changed into the integrated tubular column of exploration production and development production so as to reduce the safety ricks. Thirdly, the technology of multistage injection, temporary plugging diversion and sand-adding acid-fracturing was created for 180℃ ultra-temperature and 5 000 m ultra-deep carbonate reservoirs to achieve the volume fracturing objective of inter-layer temporary plugging and inner-layer diversion. Fourthly, the carboxymethyl fracturing fluid and acidizing fluid systems applicable at 180℃ ultra-high temperature were preferentially used, and the viscosity of fracturing fluid through 120 min shearing at 180℃ and 170 s-1 still remains 80 mPa·s. Through 60 min shearing at 180℃ and 170 s-1, the viscosity of acidizing fluid reaches 30 mPa·s. The above technology was widely applied in Well Antan 1x with the pumping rate of 11 m3/min to ensure the 6 h safety and high-efficiency implementation as well as subsequent safety and stable production for a half year and above under all kinds of adverse conditions including large scale (3 000 m3), high pressure (80-90 MPa), multiple combination with liquids (fracturing fluid and acidizing fluid)and ultra-high temperature (180℃). Proven by micro-seismic monitoring and simulation, the stimulated reservoir volume was increased by 3.5 times than the past technology to realize the length-width-height 3D simulation. After fracturing, daily gas production was 40.9×104m3, daily oil production was 71 m3, the pressure of pilot production well head kept over 25 MPa, and stable daily gas production reached 10×104m3, which achieved the integrated design objective of exploration, development, geology and engineering. © 2018, Editorial Office of ACTA PETROLEI SINICA. All right reserved.