Shale oil and gas wells had drastic decline characteristics in the first few production years. Operators may have to drill new wells or re-fracturing the well to maintain the same production level. Properly designed and implemented re-fracturing stimulation will improve the EUR as much as two-fold.
In this paper, we present a practical methodology to model re-fracturing operation and predict the shale gas production after re-fracturing in the shale gas reservoirs. In this approach, a new mathematical model is presented to improve the understanding of the correlation between the micro-seismic magnitude and the shape factor in the dual-porosity system. Shape factor can characterize the fluid transfer between matrix and fractures in the system, and micro-seismic mapping has been widely used to monitor hydraulic fracturing responses and to evaluate stimulation results in shale gas production. Application of dual porosity model allows accurate modeling shale gas flow in fractured reservoirs, which incorporates heterogeneity of the reservoir and corrected permeability by Langmuir isotherm. Analyzing micro-seismic locations and magnitudes provides useful information of the induced fractures, such as fracture orientation, width, spacing, etc. The shape factor is dependent on fracture characteristics and micro-seismic magnitudes, which is estimated by history match analysis of 6 shale gas producing wells in the Longmaxi play. The shape factor function and the permeability of induced fractures are then modified with the new micro-seismic data by the proposed mathematical model to estimate the shale gas production after the re-fracturing treatment.
Comparing the simulated results with well production history, the present model is able to accurately estimate the shape factor in the dual-porosity model, which consequently enhances the prediction of shale gas production. According to stimulated fracture network, dead gas area, and production enhancement, re-fracturing candidates are selected and evaluated with high production decline rate.
The proposed mathematical model is important to simulate and optimize re-fracturing in shale gas productions. A robust mathematical model that accurately describes the micro-seismic data and the shape factor is presented and essential to better forecast and optimize shale gas production during the lifespan of the well. We presented a process on how to design and plan for a re-fracturing stimulation.