Analysis on the pressure dynamic characteristics of slanted well in dual-porosity and dual-permeability reservoir

In order to understand the dual-permeability flow law of slanted well in a fractured reservoir and study the characteristics of pressure dynamics, a flow model of slanted well in a dual-porosity and dual-permeability reservoir is established. The model is solved by Laplace transformation, separation of variables, and superposition of sink source functions, etc. The analytical solution of bottomhole pressure change in Laplace space is obtained. A series of pressure dynamic characteristic curves of slanted well in dual-porosity and dual-permeability reservoirs are programmed and drawn by Matlab software, which are controlled by varying model parameters such as the permeability ratio of fracture system to total system. Based on the pressure dynamic characteristic curves, seven flow regimes are identified, including pure well bore storage effect stage, skin effect stage, early radial-flow, middle linear-flow stage, transitional flow stage, inter-porosity flow stage from matrix to fracture and late radial flow stage. In particular, the differences of flow characteristic curves among slanted well, vertical well and horizontal well are analyzed. It is found that slanted well has more early radial-flow stage and middle linear-flow stage than the vertical well, and these two flow regimes have shorter duration than the horizontal well. In addition, the effect of inclination angle of well, well length and other parameters on the characteristic curve is analyzed. The larger the inclination angle and well length, the lower the curve position, the more obvious the early radial flow stage and the middle linear flow stage. The larger the permeability ratio of fracture system to total system is, the more significant the inter-porosity stage is and the deeper the inter-porosity concave is. The proposed analytical model and a series of pressure dynamic characteristic curves can be used to study the seepage characteristics of slanted wells in fractured reservoirs.