科研之友
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摘要
A new formulation of the wellbore-boundary condition in multiphase-reservoir simulation is suggested, allowing automatic determination of the direction of the flow at any time. It is particularly useful in coupled transient modeling of the liquid-loading phenomenon in gas wells. The traditional inflow-performance relationship (IPR) uses a common-wellblock productivity index (PI), but determines the inflow/outflow of the individual phases through a wellbore connection in an otherwise detached manner. The new approach takes into account that all phases should flow in the same direction and should have a common zero-flow condition. The restriction leads to the definition of a new state variable: the multiphase zero-flow pressure (MPZFP or P-0). According to the new formulation, the flow direction at the connection is determined by the sign of the difference between this gridblock variable and the wellbore-flowing pressure. Advantages of the new formulation include that the flow is always cocurrent through a single connection (but multiple connections can lead to crossflow); that the meaning of wellblock PI is preserved; that the phase composition of the connection stream is determined by the upstream condition; that when wellbore pressure is far from the MPZFP, the traditional (detached) IPRs are recovered; and, last but not least, that previous numerical-convergence problems are completely eliminated during coupled dynamic simulation of the wellbore/reservoir system in the presence of significant capillary pressure. Examples illustrate the application of the new wellbore boundary condition in coupled modeling of the complex phenomena usually referred to as liquid loading.
- 出版日期2015-6
