The Wellbore-Reservoir Coupled Discrete Pipe Element Model For Horizontal Well Production

The technology of uniform injection and production of horizontal well plays an important role to EOR(Enhanced Oil Recovery)for heavy oil thermal recovery,the design of injectionproduction wellbore needs to know the distribution of thermal and hydraulic parameters along horizontal well.The coupling between pipe flow in wellbore and porous flow in reservoir during injection and production is complex,which is still the most one of the difficult problems in reservoir simulation at present.A discrete model of hydraulic pipe element,based on mass,momentum and energy conservation and the variation law of fluid dynamics parameters for horizontal wellbore-reservoir coupling,were established.The main works are as follow:(1)The pressure drop and heat loss of steam injection in vertical well were calculated and the variation and sensitivity of thermodynamic parameters of steam injection in vertical well were studied according to the traditional wellbore steam injection thermodynamic model.It was shown that the pressure,steam quality and steam injection rate at the wellhead have significant effects on steam quality and pressure of bottom hole fluid.(2)The flow and heat loss model of variable mass horizontal well was established with the thermodynamic parameters at the vertical well bottom were taken as the boundary conditions at the heel of horizontal well.The variation law of flow rate and pressure during steam injection in horizontal well was analyzed by thermal recovery simulation software CMG with considering the effects of variable mass flow characteristics and the frictional pressure drop along horizontal well.(3)The pipe flow in 1D horizontal wellbore and porous flow in 2D reservoir were represented uniformly as flow in pipe element with different flow resistance characteristics.The wellbore-reservoir coupled discrete pipe element model was established with the geometry space of wellbore and reservoir was discrete according to the pipe element with 2D vertical and horizontal distribution.The numerical model was transformed into a set of nonlinear algebraic equations with node pressure as unknown quantity according to the physical relationship between the flow rate and the pressure of the pipe element based on the conservation of flow rate at the wellbore-reservoir pipe element nodes.The numerical results obtained by Newton's method were in good agreement with the result of CMG reservoir simulation which verifies the robustness of the discrete pipe element model.(4)The pressure and velocity distribution in horizontal well steam injection was calculated numerically with the discrete pipe element model program developed in this paper.A unified discrete pipe element model that considering the throttling resistance characteristics of the injection hole was used to optimize the steam injection wellbore parameters in horizontal well and some results with engineering significance were obtained.