Analysis of Slug Test Data From Hydraulically Fractured Coalbed Methane Wells

This paper presents new type curves for analyzingslug tests in hydraulically fractured coal seams. The type curves were viable producers, Therefore, these conventional slug test analysis developed using a finite-conductivity,vertical fracture model and techniques cannot be used to either assess the success of the fracturetreatmentor to evaluatethe px.t-fracture potentialof these are presented in terms of three parameters -dimensionless stimulated coal seams. Karsaki, et al,g studied the pressure welltme storage coefficient, dimensionlessfracture conductivity, response of slug tests in infinite-conductivity vertical fractures, and fracture-face skin. Whh these new curves, we may estimate but they did not investigate the behavior of finite-conductivity the hydraulic fkacturehslf-length, the fomlation permeability,and fractures. The purposes of this paper are to develop a male] for the fracture conductivity. We also present a procedure for using slug testingin coal seamswith finite-conductivityverticalfractures the new curves and illustrate the procedurewith an example, and tc illustrate application of this model to the analysis of slug ;ests, INTRODUCTION Slug testing has been proven to & an effective method for MATHEMATICAL MODEL characterizing the production potential of coal seams. A slug test We developed our slug test model using Cinco-ky, et al.’sg involvesthe impositionof an instantaneouschange in pressure(m fluid head) in a well and the measurementof the resulting change model which considers a well intersected by a fully-penetrating, finite-conductivity,vertical fracture. The reservoir is assumed to in pressure as a function of time. This change in pressure is be an isotropic,,homogeneous, infinite medium having a uniform created by either injecting into or withdrawing from the well a specific volume of fluid (i.e., a slug), From this measured thickness, h, permeability, k, and porosity, @. In addition, the pressure response, we may estimate the permeability and nearrescrvoir contains a slightly compressible fluid of viscosity, p, welltmreconditions. and compressibility,c, that are independentof pressure. Initially, slug testing methods and analysis techniques were developed for estimating the transmissivity of shallow, Cinco-Lcy, et al’sg modci assumes the fracture to be a homogeneous, uniform slab with height, h, width, bj and half underpressured aquifersl-s, but also have found applications in length, L { Because the fracture width is much smaller than the petroleum industry, especial)j for analyzing the flow period fracture ength and height, the model assumes the flow in the during drill stem tests4-6. Recently, slug testing has been fracture is linear and that fluid influx at the fracture tips is extended to the evaluation ot’ the production potential of coal negligible, In addition, the model assumes that fluid production seams7. Since most coal seams are saturated initially with water, from the reservoir to the wellbore occurs only through the slug testing provides a simple but effectivemethod for estimating fracture. Further, since the fracture volume is small, the model flow properties early in the productive life before the initiation of neglects the fracture compressibilityand assumes flow within the gas production. Reference 7 provides an overview of fractureis relativelyincompressible. Additionaldetailsconcerning conventionalslug testingin coal seams. the model formulation and problem solution may be obtained in Ref. 9 and Appendix A. Conventional slug test analysis techniquesare based on radial flow models, However, many wells completed in coal seams Under these conditions, Cinco-Ley, el al.g derived art require hydraulic fracturing in order to become economically expression for the dimensionless pressure drop at the wellbore (i.e., XD = O) during constant rate production from a WCII Referencesand illustrationsat end of paper intersectedby a finite-conductivityfractureas --2 Analysisof SlugTest Data From HydraulicallyI%ctured CoalbedMethaneWells SPE 21492