The major challenges of shale reservoir development in Weiyuan gasfield are: (1)strong geologic heterogeneity, such as geo-stress, horizontal lamination, limited complexity and propagation of hydraulic fracture; (2)casing deformation, which caused the reservoir fractured insufficiently for many engineering problems. To avoid the problem above and increase complexity and SRV of hydraulic fracture, a deeply fracturing technology (DFT) was proposed, which was validated available and had been applied in 20s wells. Based on ununiform distribution of geo-stress, the mechanism of DFT is using temporary plugging materials to fracture the reservoir sufficiently, which can be classified in 3 major patterns, include Intrasegment/Multi-segments/Closely spaced fracturing. Firstly, according to reservoir and stimulation objectives, choosing the appropriated development pattern. Then, considering geological and engineering factors, the optimization of temporary plugging materials and pumping parameters are needed in making pumping schedule. Finally, conducting fracturing by the schedule, and combined with operation curve and micro-seismic data, choosing proper time to release temporary agents. With the application in the field, some conclusions are as follows:(1) Intra-segment development pattern was preferred in single-segment sufficient simulation; multi-segment was favored in the development of multi-stages without bridge plug situation, especially in the stimulation of casing deformation intervals. Which also improved operational timeliness; Closely spaced perforation pattern was benefit for the segment with big geo-stress difference and the well with small well spacing.(2) DFT was validated available by fracturing curve and micro-seismic monitoring. Event response points coverage rate of segment was 100%, SRV per segment and micro-seismic events were increase by 11%-45% and 54%-429%, respectively.(3) A combination of temporary plugging ball and powder was recommended, and the optimal agents pumping rate was 3m3/min. With the treatment above, pumping pressure was increased after agents released, the peak increment is 10 MPa, plugging effect was clear. DFT is suitable for high heterogenous horizontal interval development, and also can be combined with bridge plug to achieve segment sufficient fracturing. The most important is, it is available in casing deformation interval stimulation, which is so serious in Weiyuan gas-field.
Production history fitting in Weiyuan shale gas shows that the length and height of supporting fractures are short, which limits the long-term conductivity of fractures. Due to the limited volume of reconstruction, the production decreases rapidly, which makes it difficult to achieve the purpose of economic and effective exploitation. In view of the above problems, an enhanced hydraulic fracturing technology (EHFT) which has been verified and applied is proposed to increase effective SRV. according to the different characteristics of shale reservoir, EHFT optimizs the performance parameter of fracturing fluid and matchs different modes of proppant injection, which can be classified in 4 major patterns, including modes of proppant injection in long/short slug type and densifying proppant injection in long / short slug type. First, based on brittleness evaluation and mineral composition, and combined with interpretation results of the natural fracture, the pumping plan is made according to the design goal. Then, modes of proppant injection is adjusted and optimized in real time through the construction curve and micro-seismic data during fracturing. The hydraulic fracture propagates along the dominant channel in the process of fracturing and there is the risk of the fracture communicating with the adjacent well. The fracture control technology of multi cluster perforating can effectively avoid it. Through field application, the following conclusions are drawn: (1) For reservoirs with high clay content, high viscosity fracturing fluid is recommended to improve the fracture width and reduce the complexity of construction; modes of proppant injection in long slugs of low concentration can control the construction scale, improve quality of proppant per meter, establish continuous fracture support and improve the long-term conductivity; modes of proppant injection in short slug type can control the fluid loss and avoid the occurrence of complex conditions, which is especially suitable for reservoir with natural fracture. (2) In the process of fracturing, the combination of various modes can achieve good results through real-time analysis and judgment. (3) The effectiveness of EHFT is verified by construction parameters, fracturing curve and micro-seismic monitoring. The construction scale (total volume of fracturing fluid) is reduced by 10%; quality of proppant per meter is increased by 10-20%; the fluctuation range of construction pressure is controllable/small; and the SRV and micro-seismic events are significantly increased. (4) The test production of well A which is the highest in Weiyuan is 71.2×104m3 with this technology. EHFT is suitable for the complexity of shale reservoir reconstruction. Multiple modes of real-time control can reduce the occurrence probability of complex conditions, improving the effective SRV and achieving efficient fracturing. Most importantly, the technology is feasible and effective in the overall goal of cost reduction and efficiency increase
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