New Inflow Performance Relationship for Coalbed Methane Wells

摘要

The inflow performance relationship (IPR) plays an important part in well completion, well production optimization, nodal analysis calculations, and artificial lift design. The production of coalbed methane is different from the conventional gas. For coalbed formation, permeability is sensitive to changes in effective horizontal stress which includes a cleat compression term and a matrix shrinkage term that have competing effects on cleat permeability. Therefore, the conventional method to calculate IPR curve is not completely appropriate for coalbed methane. The production of under-saturated coalbed methane reservoir can be divided into three distinct stages-: single water phase, multiphase gas and water, and single gas phase. Previous literatures either neglect the matrix shrinkage which results in increasing production rate at a given bottom hole pressure or only focus on the last single gas phase stage. This paper presents a new method to calculate the IPR curve for coalbed methane reservoir in the presence of permeability dynamics with pressure based upon P&M or Shi model. A second objective of this paper is to develop an approach for multiphase flow which requires a relationship between relative permeability and pressure, analogous to Fetkovich’s method for oil and gas flow. The methodology is further validated with field data from Qinshui Basin in China. The results indicated that the tool proposed here provides reservoir enginners with a quicker and easier way to estimate the performance of coalbed methane well.