Production Data Analysis of CBM Wells

Abstract

fax 01-972-952-9435. AbstractRecent advances in production data analysis (PDA) techniques have greatly assisted engineers in extracting meaningful reservoir and stimulation information from well production and flowing pressure data. Application of these techniques to coalbed methane (CBM) reservoirs requires that the unique coal storage and transport properties be accounted for. In recent work, the authors and others have demonstrated how new techniques such as the flowing material balance (FMB) and production type-curves may be adapted to account for CBM storage mechanisms (i.e. adsorption), but to date the focus has been on relatively simple CBM reservoir behavior. Although adaptations of PDA to include more complex CBM reservoir characteristics were introduced, the focus of the current work is advancement of modern PDA techniques to incorporate reservoir behavior such as single-phase flow of water in undersaturated reservoirs, two-phase (gas+water) flow in saturated reservoirs, effective permeability changes during depletion, and changing gas composition due to relative adsorption. Specifically, the FMB technique is modified in this work to include several complex CBM reservoir characteristics. FMB can be a powerful diagnostic technique when relative and absolute permeability changes are apparent during depletion. Several synthetic and field examples are given to demonstrate how FMB, type-curve analysis and analytical simulation can be used in parallel to provide a particularly useful data analysis tool.The adapted PDA techniques used in this work make use of the pseudotime and pseudopressure concepts, modified to account for CBM reservoir behavior, to linearize the (constant-rate) diffusivity equation for CBM.Material balance pseudotime was used to account for variable operating conditions. These techniques were used successfully to extract quantitative reservoir information from single-and two-phase CBM simulated and field production and pressure data. The techniques for two-phase CBM require further evaluation, however.Several key assumptions were used in deriving the PDA techniques including (but not limited to) instantaneous desorption (small sorption times) and single-layer behavior. Although the former is not considered a serious limitation, as most commercial reservoirs analyzed to date by the authors have exhibited single-porosity behavior during production, the latter may be quite important for some producing fields. PDA of multi-layered CBM reservoirs will be discussed at length in a future paper.

Selected topics in coalbed methane reservoirs

“…(Gerami et al, 2007) illustrated, through mathematical derivation, that the solution to flow equation for gas reservoirs could be extended to CBM reservoirs if the definition of total compressibility is modified to include sorption compressibility. The same concept, with no mathematical derivation, was previously suggested by Spivey and Semmelbeck (Spivey and Semmelbeck, 1995) and Clarkson et al (Clarkson et al, 2006). As such, total compressibility as defined in Equation (12) was further modified to: c t ¼ c f þ s w c w þ s g c g þ c d (14) Sorption compressibility, similar to gas compressibility, is a strong function of pressure and becomes increasingly more important as reservoir pressure declines.…”

“…Clarkson et al (Clarkson et al, 2006) described a method for calculating relative permeability by history matching the fieldspecific production and flowing pressure data, back calculating effective permeabilities to gas and water and estimating the relative permeability to gas and water from the estimated effective permeabilities. In a more recent study Clarkson et al (Clarkson et al, 2010) investigated the impact of reservoirs drivers, such as absolute permeability shrinkage/growth and multi-layer reservoirs on relative permeability curves of a CBM reservoir.…”

Calculation of dynamic loads of the sucker rod pumping system in CBM wells

“…The polished rod load as a function of time during one complete pumping cycle sums up the following categories of load: static, inertial, loads generated by vibration and hydrodynamic friction phenomena. Many authors have developed approximate computational formulas calculating polished rod load, including API, Вирновский А.С., Вирновский А.С.-Адонин А.Н., Kemler Emory and Mills (Everitt and Jenings, 1992;Hein and Hermanson, 1993;Chen and Wang, 2000;Qu et al, 2004;Clarkson et al, 2007). Among these relationships, some only considered inertial load, while others only considered vibration load.…”

Developing synthetic reservoir type curve model for use in evaluating surface facility and gathering pipe network designs

“…Clarkson et al (2007); Case 06 production data from Horseshoe Canyon taken from Okuszko et al (2008); Case 07 taken from Salmachi & Yarmohammadtooski (2015) for CBM production data in San Juan basin; and Case 08 taken from Mazumder et al (2003) from Surat Basin CBM production data. Referenced data points have been digitised from raster images and is reproduced as faithfully to the original sources as possible.…”