With the development of tight oil reservoirs, various fracture-propagation models have been used to maximize the contact area between fracture network and reservoir matrix. However, the optimal results doesn’t necessarily obtain the maximum economic benefits. Also, many researchers developed reservoir simulators to optimize fracture parameters (e.g., half length, width, direction, et al.). However, these parameters are not controllable in the field operation. Therefore, there is an urgent demand to optimize the controllable parameters (e.g., perforation diameter and spacing, pumping speed and total fluid volume, et al.) for multi-stage hydraulic fracturing.
In this work, we present a framework coupling fracture-propagation and reservoir simulation to optimize tight oil production. First, we employ extended finite element method (XFEM) to simulate fracture propagation, taking the effects of stress-shadow, natural fracture and fracturing fluid leak-off into account. The simulation results are validated by micro-seismic data. Then fracture parameters (i.e., fracture geometry, width and permeability) are extracted and discretized. After that, we use embedded discrete fracture model (EDFM) to build the fracture model and embedded into a compressible reservoir simulator. Notably, non-linear flow in tight oil matrix and pressure dependent permeability of hydraulic fractures are considered in our reservoir simulator. Finally, the production performance and economic profits are evaluated.
In order to demonstrate the reliability of our framework, a field well performance in Jimsar Sag of the Xinjiang oilfield is firstly analyzed. Then the effect of some controllable parameters were investigated. The cluster number within a given stage ranges from 2 to 6. Three values of perforation spacing were considered including 100, 200, and 300 ft. Results reveal that stress-shadow effects can be reduced with two clusters per stage, and small perforation spacing would benefit tight oil production and economic profits. Through changing perforation diameters, the effect of different pumping speed and total fluid volume are also discussed. Furthermore, we studied the effect of three multiwell-completion schemes (i.e., sequential, zipper, and simultaneous fracturing). Results show that the zipper-fracturing technique is superior to other schemes.
Our framework can provide effective guidance for the design of horizontal drilling and hydraulic fractures, which can be further combined with optimization algorithms to improve the efficiency.
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