Study on repeated stimulation technology and its application to in low-yield horizontal wells in ultra low permeability oil reservoirs, Changqing Oilfield

In the Ordos Basin, the production rate of some horizontal wells declines signifcantly to the low value for the reservoirs are tight with low pressure, the completed wells are less stimulated and long-term injection and production displacement cannot be established easily. In this paper, history match was performed on the production performance of typical injection-production pattern of horizontal well to investigate the oil reservoir pressure and remaining oil distribution characteristics. Volumetric fracturing and energy complement was integrated for repeated stimulation design so as to enlarge reservoir stimulation volume, increase fracture complexity, recover fracture network diversion, remove deep blockage and improve formation energy. Then, the technological model for the stagedenergy complement and repeated volumetric fracturing of horizontal well was established, i.e., "high fow rate injection, two-stage temporary plugging for boosting, multi-functional fracturing fuid, and post-fracturing shut in for diffusion", and its support compression string with twin packer and single slip was developed. The optimized fow rate is 4-6 m³/min, there is two-stage temporary plugging for diversion at the opening and inside of fracture, the fuid volume in each section is 800-1 000 m³and shut in period after fracturing of each section is 1-2 d. It was tested on site in 5 horizontal wells in ultra low permeability oil reservoirs in the Ordos Basin. Energy complement and repeated fracturing is carried out at 5-6 sections in each well, and average daily oil production of each well is increased from 1.6 t to 6.2 t, which is equal to its production rate at the early stage of commissioning. And its oil increment is 100% higher than that of the wells which are treated with the conventional repeated fracturing in the same block. The formation energy of the well group rises by 2-4 MPa, the cumulative oil increment is over 1 200 t one year, and yearly decline rate is 38% lower than that after the initial fracturing of this well. This technology can be used as the reference for increasing the production rate and ultimate recovery factor of old horizontal wells in unconventional reservoirs.