Production Data Diagnostics based on Inflow Performance Relationship of pumping wells in CBM Fields

Abstract

Abstract Coal Bed Methane (CBM) is a type of unconventional resource wherein methane gas adsorbed on surface of coal seams is produced by dewatering waterfilled coal seams and thereby causing desorption of the gas. This paper aims at applying quick look diagnostic curves to assess performance of Coal Bed Methane (CBM) wells which traditionally encounter high frequency workovers with reservoir heterogeneity and complex physics. Currently, very few production diagnostic tools are available to access / predict unconventional Coal Bed Methane (CBM) well behavior. Use of production diagnostic curves using pressure-rate data is presented to distinguish the well performance with variety of completion types and artificial lift strategies which provides gainful insights into relative well performance. Inferences could be used to plan / optimize for future development strategies for infill drilling. Response based diagnostic tools are derived using P-Q (Pressure-Rate) and PI-Cum. (Productivity Index - Cum. Prod.) plots and extrapolation of trends can be used to guesstimate the expected ultimate recoveries and drainage area for CBM wells. Thus, typical characteristics of these performance plot gives clear indication of qualitative desorption front. Diagnostic P-Q and PI-Cum. performance curves were generated for various on-stream CBM wells and these curves were used to identify and predict the flow regime in wells with different completion scenarios. Single phase Inflow-Performance Relationship (IPR) shows a typical behavior in most of the wells and analysis of life-cycle IPR indicates a characteristic signature for on-set of pseudo-steady state (PSS). Flow regimes which can be clearly identified are initial flow i.e. Infinite acting radial flow (IARF), completion/intervention dependent flow and PSS flow. The initial flow period involves dewatering of coal seam and hence generates a hyperbolic curve on the p-q plot. As desorption front advances further, peak gas production is observed and this phase can be prolonged by effective use of Artificial lift (AL) strategies to maximize the drawdown. The well soon shows positive slope line on IPR that corresponds to Pseudo-steady state or Boundary dominated flow. At this juncture the drainage boundary of the well is properly defined and so is the Expected Ultimate Recovery (EUR). This phase is the longest in terms of well life cycle. These diagnostic tools were highly useful in well and reservoir performance analysis to optimize the AL and workover practices for CBM wells. This paper brings out novel approach towards analysis of production data from CBM field with wells operating on Progressive Cavity Pumps (PCP's) to dewater coal beds, it brings out a way to qualitatively estimate the desorption front and quantitatively deduce the EUR’s of the wells. This paper proposes a way to generate "Type well" analysis for CBM field and augment a reliable production forecasting.