Buried in loose and fine-grained sandstones, heavy oil is widely found at the depth of 3256- 3417m in Block KM Yumen Oilfield, China, taking up 4.1 square kilometers. It is known for its low permeability (25.97*10-3μ㎡), high density (0.973kg/L) and viscosity (12708mPa·S). There is a thick interlayer above it, while an aquifer is only 3m beneath it. Thus, fractures may extend downward and perforate the aquifer, which causes water fingering. Effects of propped fractures of various shapes and their conductivities on production were simulated via ABAQUS, therefore the fracturing scale and appropriate fracture shape were selected. Flow resistance tests were applied on many applicable diverting agents in the lab and the high density diverting agent FJ was selected. A small scale fracturing experiment was carried out prior to the hydraulic fracturing operation, so that stratigraphic properties and the fracturing fluid’s performance could be studied in advance. Based on the curve of production rates affected by propped fractures with various shapes and conductivities, short and wide fractures with a conductivity of 60μ㎡·cm shall be adopted. The environment temperature of fractures goes down as the water based fracturing fluid enters the reservoir, which increases the viscosity of heavy oil and restricts formation fluids from penetrating fractures. Therefore, the benzene organic solvent shall be used as a spacer fluid to isolate tight oil and the fracturing fluid. In order to keep fractures from extending downward and damaging the aquifer, an artificial isolation zone is established by the high density diverting agent FJ that builds up a solid low-permeability interval along the low edges of fractures. The low density ceramsite is optimized and used as the proppant. In the fracturing experiment the benzene organic solvent is pumped first to make fractures while isolating heavy oil, then active water with the high density diverting agent FJ enters the reservoir to build up the protection zone. The displacement fluid is pumped to push FJ into fractures. The well is shut in for 10-15 minutes prior to sand fracturing in order to make FJ distributed evenly. Wells in the region used to be developed intermittently, while the above integrated technologies improved the daily production rate by 2.63 times and it has stayed 8-10t/d since the last 6 months. Integration of the spacer fluid, fracture control technique and proppant optimization significantly contributes to heavy oil exploitation in KM Block, Yumen Oilfield.
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