西南石油大学学报(自然科学版)

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Unsuitability of Using Superposition Principle to Solve Equation Incorporated with Threshold Pressure Gradient

Li Daolun1,2*, Yang Jinghai3, Zha Wenshu2, Wang Lei4, Lu Detang1   

  1. 1. Department of Applied Mathematics,Hefei University of Technology,Hefei,Anhui 230009,China
    2. Department of Modern Mechanics,University of Science and Technology of China,Hefei,Anhui 230027,China
    3. Logging & Testing Services Company,Daqing Oilfield Co. Ltd.,Daqing,Heilongjiang 163453,China
    4. Institute of Nuclear Energy Safety Technology,Chinese Academy of Science,Hefei,Anhui 230031,China
  • Online:2015-08-01 Published:2015-08-01

Abstract:

Equation incorporated with threshold pressure gradient(TPG)is not homogeneous,and the error exists if it is solved
based on superposition principle. A mathematical single-phase flow model incorporated with the threshold pressure gradient
is proposed to describe the flow behavior in low permeability reservoirs by coupling the well storage effect. The fully implicit
numerical simulation based on PEBI grid is developed to study the transient pressure response for a vertical well. Buildup
pressure based on numerical simulation shows that TPG quickly makes buildup pressure stabilize,and makes buildup pressure
lower than initial pressure,and thus leads to the drops of curves of pressure derivative during buildup period. However,buildup
pressure based on superposition principle increases with time and cannot stabilize even after 4 800 days,which makes curves of
pressure derivative go up during buildup period. Comparing well test curves based on numerical solution with well test curves
based on superposition principle,we find that solution based on superposition principle is totally different from the solution
based on numerical simulation,which exhibits that superposition principle cannot be used to solve flow equation incorporated
with threshold pressure gradient.

Key words: threshold pressure gradient, low permeability, PEBI gridding, numerical solution, well test curves