SPE 139118 Production Analysis and Well Performance Forecasting of Tight Gas and Shale Gas Wells

Estimation of reserves in tight gas and shale gas reservoirs is problematic due to the low to ultra-low permeability characteristics of these reservoir systems. The sole application of conventional decline curve analysis methodologies often yields erroneous reserve estimates. Therefore, the use of theoretically-based production analysis techniques has become a must to analyze well performance and estimate reserves. The primary objective of this work is to develop a systematic workflow, which integrates model-based production analysis and rate-time relations, for the analysis/interpretation of well performance data in unconventional reservoirs. The major steps in the proposed workflow are: ● Diagnosis of production data. ● Construction of a base well/reservoir model utilizing static well/reservoir data as well as completion/stimulation parameters. ● Extrapolation of the model to predict well performance along with the use of rate-time decline relations. The proposed methodology is demonstrated using data from unconventional reservoirs, including a horizontal well with multiple fractures. We present the application of rate-time relations to provide estimates of time-dependent reserves. The use of βq,cp-derivative is also illustrated in distinguishing data characteristics as well as identifying issues associated with data. Rationale for This Work Unconventional reservoir systems such as tight gas sands, shale gas, tight/shale oil, and coalbed methane reservoirs have currently become a significant source of hydrocarbon production and offer remarkable potential for reserves growth and future production. Unconventional reservoir systems can be described as hydrocarbon accumulations which are difficult to be characterized and produced by conventional exploration and production technologies. Complex geological and petrophysical systems describe unconventional reservoirs in addition to heterogeneities at all scales similar to conventional reservoir systems. Because of the low to ultra-low permeability of these reservoir systems, well stimulation operations (e.g., single or multi-stage hydraulic fracturing, etc.) are required to establish production from the formations at commercial rates. Gas-in-place/reserves estimation in unconventional (low/ultra-low permeability) reservoirs has recently become a topic of increased interest as advanced technology permits the production and development of these resources domestically and internationally. Production data from unconventional reservoirs exhibit extensive periods of transient flow behavior due to the low/ultra-low permeability characteristics of these systems which often lead to the over-estimation of gas-inplace/reserves with the use of conventional rate-time relations (i.e., exponential and hyperbolic rate-time relations). Because of the uncertainty associated with reserves well/reservoir parameter estimation in unconventional reservoirs, a comprehensive workflow has to be developed. In this work we develop a workflow which includes using both rate-time and production data analysis methodologies (i.e., analytical/semi-analytical solutions) in conjunction to estimate well/reservoir properties and forecast production into future.