Simulation Study On Fracturing Capacity Of Slagted Tight Gas Reservoir

Along with the continue decrease of conventional oil and gas resources and the rapid increase of global energy consumption, the unconventional reservoirs such as low porosity-low permeability or super-low permeability fractured gas reservoirs, coalbed methane gas reservoirs and shale gas reservoirs gradually become the focus of exploration and development, which with the generality of natural fracture development and low matrix permeability. Conventional fracturing technology is difficult to achieve expected effect due to the confined control zone of main fracture and limited fluids providing ability from matrix to main fracture. So the network fracturing technology is adopted to stimulation this kind of reservoirs effectively. Due to influence factors such as random distribution of natural fractures and the complexity of fracturing technology, the geometry of network fractures is complex resulting in extremely complex fluid flow progress. At present, existing productivity models of network fracturing all simplify the distribution of natural fractures and the geometry of network fractures, which can’t completely meet the requirements of network fracturing simulation in natural fractured reservoirs (NFR). So, a further developed productivity prediction method of network fracturing in NFR is required.After sufficient research of fractured reservoir modeling and network fracturing productivity model, this paper establishes a network fracturing productivity prediction model in tight gas reservoirs, which is based on the equivalent continuous model of fractured medium with the integrating advantages of continuous medium model and discrete fracture network model. The main content of this paper is as follows:(1) The post-frac fracture distribution model is built by adding the network fractures parameters into the discrete fracture network by applying probability and statistics, stochastic theory and Monte-Carlo method to process the reservoirs natural fracture statistics data.(2) The post-frac fracture distribution model is discretized into finite number grids, and the seepage equation of fracture system and matrix systems with periodic boundary is solved by the boundary element method. The equivalent permeability tensor of grid is calculated according to equivalent principle, and the sensitivity analysis of influence factors are done as well. The fracture network productivity model in fractured gas reservoirs is established in which homogeneous anisotropic continuum media represented by equivalent permeability tensor is used instead of the original fractured media. The model fully considers the influence of natural fracture distribution and complex fracture network on the fluid flow, and it can adapt to all kinds of non-conventional fracture network and accurately predict production performance of network fracturing well.(3) WM(Wire-mesh Model) and UFM(Unconventional Fracture Model) are utilized to analyze fracturing well productivity, the results show that the network fracturing can greatly improve seepage environment around the well, increase the single well control area and significantly increase stimulation effects. In the same SRV(Stimulated Reservoir Volume), stimulation effect is mainly affected by the fracture interval and fracture opening in the network. The production of network fracturing wells is mainly affected by the following three aspects with mutual restriction and coordination:first, the providing fluid ability from matrix to fracture network; Second, from fracture network to the main fracture; Third, from the main fracture to wellbore. Fracturing rate and fluid volume both have positive impacts on the network size, fracture aperture and total fracture length. Besides, large rate and liquid volume are more apt to form large-scale complex fracture network, improving the single well production. Considering economic factors and limited control area of single well, it is required to optimize the rate and fluid volume according to stimulation requirement and control zone of single well.The studies of this paper have important guiding significance on the design and assessment of network fracturing in NFR, and can provide referable research methods and techniques for the seepage simulation in complex reservoir.