Study On Productivity Prediction And Optimal Design Method For Complex Structure Wells In Gas Reservoirs

With the increasing scarcity of oil resources and the rising of oil prices, the switch to arelatively inexpensive natural gas as commonly used fuel has become a society-wideconsensus. The main component of natural gas is methane, and it has many advantages, suchas complete combustion, cleanliness and pollution-free. So it meets the global advocate of theidea of green energy. Natural gas resources abound in our country, but most of thesesresources in low permeability formation with low porosity and poor connectivity. It is difficultto exploit the formation effectively by using single vertical wells and conventional horizontalwells. In recent years, fractured horizontal wells and other complex structure wells have beenapplied to the gas reservoir development, but there are few researches on the productivityprediction and optimal design method for complex structure wells in gas reservoirs. How topredict and evaluate the performance of complex structure wells in gas reservoirs accurately isone of key problems in efficient development of gas reservoirs. Therefore, the productivityprediction and optimal design method for complex structure wells in gas reservoirs isdeveloped in this paper, and the following work has been done:Firstly, considering the influence of various cracks of unequal length, spacing,conductivity, asymmetric about the horizontal wellbore and angle with the horizontal wellboreon productivity of fractured horizontal wells, the coupling model of gas reservoir percolation,fracture percolation and wellbore percolation for fractured horizontal wells is developed andsolved. The three dimensional percolation characteristic of fractured horizontal wells isconsidered in the gas reservoir model, the pressure drop in fracture is considered in thefracture model, and the effect of pressure drop caused by the friction and the fluid inflow fromgas reservoir is considered in the wellbore model. The productivity prediction formula forfractured horizontal wells is provided, and influencing factors on the productivity areanalyzed.Secondly, the coupling model of gas reservoir percolation and wellbore percolation formultilateral horizontal wells is developed and solved. The three dimensional percolationcharacteristic of multilateral horizontal wells is considered in the gas reservoir model and theeffect of pressure drop caused by the friction and the fluid inflow from gas reservoir isconsidered in the wellbore model. The productivity prediction formula for multilateralhorizontal wells is provided, and influencing factors on the productivity are analyzed.Thirdly, the coupling model of gas reservoir percolation and wellbore percolation forherringbone multilateral horizontal wells is developed and solved. The three dimensionalpercolation characteristic of herringbone multilateral horizontal wells is considered in the gasreservoir model, and the effect of pressure drop caused by the friction, the fluid inflow fromgas reservoir and the fluid mixed at the confluence of main wellbore and branched one isconsidered in the wellbore model. The productivity prediction formula for herringbonemultilateral horizontal wells is provided, and influencing factors on the productivity are analyzed.Finally, based on the principle of orthogonal experimental design, the productivityoptimal design method for complex structure wells in gas reservoirs is founded. Influencingfactors on the productivity of complex structure wells are comprehensive analyzed, anddetermine the primary and secondary order. On this basis, further define the optimalcombination of parameters for complex structure wells.