Based on flow characteristics of horizontal wells in naturally fractured reservoirs,vadose area is divided into two zones: near wellbore zone and far wellbore zone.The far wellbore zone is featured by its continuous homogeneity.In near wellbore zone,a coupling model is established considering fluid flow in fracture and horizaontal well simultaneously.Principles of potential superposition and mirror reflection as well as the concept of infinitesimal line congruence are used in the model.Combining flow characteristics of the far and near wellbore zones,a comprehensive computational method for fractured hoizontal well productivity is presented.A practical case is used to verify this method.Computational result shows that productivity of horizontal well calculated with this method is closer to actual flow rate than theoretical formula.Productivity of horizontal well increases as fracture density rises,but increment of productivity decreases as fracture density increases.

An unsteady model of fractured horizontal wellbore coupling with a box-shaped reservoir is constructed with consideration of anisotropy in a low permeability reservoir. Solution of the model is shown. Pressure drops of friction and acceleration are considered under different types of constraints. Flow condition in fractured horizontal well is divided into early transient period and pseudo-steady period. In transient period, the output from each fracture differs little, and total production rate increases linearly with fracture number. In pseudo-steady phase, production rate of fractures at the toe and heel is higher than that in the middle. Fractures in symmetrical position have different yield due to frictional and accelerational pressure drops. Pressure loss along the wellbore results in decrease of production in horizontal well and non-uniform distribution of pressure in wellbore. Under constant flow rate followed by constant bottom-hole pressure constraints, production plateau stays longer with increase of fracture number.