The Method And Application Research Of Welltest In The Carbonate Reservoir With The Condensate Gas

The gas condensate welltest analysis in the carbonate reservoir has been always faced with tremendous difficulties due to complex reservoir rock characteristics, fluid component and phase behavior change in porous media. Multiphase flow characteristics are always occurred during the gas condensate well test and this phenomenon has been described in detail in this paper. And a new method is proposed with a comprehensive thinking of surface, wellbore, and formation system to improve the well test design program; it is significant for the production prediction and productivity analysis of condensate gas well in the carbonate reservoir.More specifically, during the period of gas condensate production and well test in the carbonate reservoir, the occurance of liquid dropout in the near-wellbore region result in multiphase flow of fluids through porous media and wellborn in case the flowing bottomhole pressure falls below dew-point, and it can be seen that the outflow parameters will change continuously during the welltest process, Thus made condensate gas production very complicated and difficult to predict, and the productivity of the carbonate reservoir needs evaluating dynamically.Based the theory of thermodynamics equilibrium and flow equation, a compositional mathematic model is established. Several factors are considered in the model, i.e. rock property changes and multiphase flow of gas condensate. It shows that the results of this model can be evolution of deliverability equation and description of parameter variation field during welltest process. The model will presents a basis for the study of deliverability test analysis and program design in the carbonate reservoir.In order to estimate the productivity of the carbonate reservoir accurately and incorporate the variable properties in these estimates, a new pseudo-pressure is defined to evaluate the combined effects of rock, fluid flow and reservoir property changes on well performance, Based on this new defined pseudo-pressure, a new deliverability model which takes into account variable rock properties in the carbonate reservoir is proposed. This model is different from the conventional deliverability model for the coefficients are the function of pressure and change with the producing time. A brief discussion is followed on how to calculate the productivity coefficients and decline law and it can provide valuable reference for optimizing production system of carbonate reservoir.Conbined with the well test equipment condition, a new method is proposed with a comprehensive thinking of surface, wellbore, and formation system to improve the well test design program, and it is applied to simulate several cases to evaluate the productivity of carbonate reservoir, and presents the changing principle of productivity the carbonate reservoir after pressure declines or outflow system is changed.The research above has significance for the theory and application of development of the carbonate reservoir during welltest process.