Research On Flow Charactrisctic And Reservoir Engineering Of Horizontal Wells In Low Permeability Reservoirs

Currently, horizontal wells and fractured horizontal wells are important ways to develop low permeability reservoirs, but there are only few studies related to the physical simulation of production performance and well pattern for fractured horizontal wells or horizontal wells.Firstly, the pore structure of natural sandstone outcrop was analyzed by conventional mercury injection method, and the sandstone outcrop with similar pore structure of typical low permeability formation was selected and encapsulated by resin. Then, the physical model was developed to simulate the fluid flow in low permeability reservoirs, the physical simulation system of large-scale model was established for low permeability reservoir, the physical simulation of production performance and well pattern was realized for fractured horizontal wells or horizontal well. Therefore, the characteristics of pseudo-threshold pressure gradient, pressure distribution and production decline were studied under the condition of horizontal well production. The single phase fluid flow in vertical well and horizontal well and two phase oil-water flow in five-spot well pattern were analyzed. It is indicated that when the wells produce with constant oil production by means of elastic drive, the bottom hole pressure of vertical wells decreases faster than that of horizontal wells in the initial stage. When wells produce with constant bottom hole pressure, the oil production is proportional to an exponential function of time, the initial production of horizontal wells is higher, and the production decline rate of horizontal wells is faster than that of vertical wells. By comparing the development effects of two kinds of injection-production pattern, the recovery of the vertical well injecting-horizontal well producing pattern is higher, and its development effect is better.Secondly, for the fractured horizontal wells with spindle and dumbbell-shaped distribution of fracture in Changqing Oil Field,3-D physical models were developed to simulate their production performance under the conditions of elastic drive and waterflooding. It is indicated that the oil production is proportional to an exponential function of time, the oil production of the horizontal well with dumbbell-shaped fracture is higher, but its decline rate is faster. Furthermore, the productivity formula and material balance equation of closed reservoir with elastic drive were utilized to derive the exponential form of oil production. The influence factors of oil production and its decline rate were analyzed under the condition of elastic drive. Under the condition of waterflooding, the water breakthrough of the horizontal well with spindle fracture was slower than that with dumbbell-shaped fracture, and the water cut increased more slowly than that with spindle fracture In the initial stage of waterflooding experiment, the production was dominated by the elastic drive, so the oil production of the model with dumbbell-shaped fracture was higher. When the cumulative water injected exceeded 0.2 PV, the recovery of the model with spindle fracture was higher than that with dumbbell-shaped fracture.Finally, the mathematical model of fluid exchange between hydraulic fractures and reservoirs matrix was established to study the optimization of flow conductivity of hydraulic fractures, and prove a certain fitting relationship between fluid supply capacity and flow conductivity of hydraulic fracture. The influence factors related to flow conductivity changing with time were introduced in the black oil model. The fracture parameters of fractured horizontal wells, horizontal section length and the number of injector were optimized based on the improved black oil simulator. The analytical results might provide a theoretical reference for the fractured horizontal well pattern arrangement in low permeability reservoirs.