A complementary approach for uncertainty reduction in post-flowback production data analysis

Abstract

A key limitation of conventional post-flowback production data analysis is non-uniqueness of solution. This causes uncertainty in reservoir parameter estimates and hydrocarbon forecasts. This paper proposes a complementary approach, using flowback data analysis to constrain post-flowback data analysis and reduce uncertainty in output results.This study history-matches two-phase pressure and rate data from seven multifractured Horn River shale-gas wells to investigate the benefits of analysing both flowback and post-flowback data together. The flowback history-match result estimates the pore-volume of active fracture networks, effective half-lengths and initial gas volume in hydraulic fractures during flowback. Also, the field production forecasts from the flowback history-match yield lower gas rates compared to actual post-flowback production data. On the other hand, the post-flowback history-match results overestimate effective half-lengths when compared to flowback history-match results. These observations are due to neglecting the secondary fracture and gas desorption effects on the dual-porosity based flowback model used in this study. The communication interface between secondary fractures and hydraulic fractures significantly increases during post-flowback periods (when most of the water in the active secondary fractures have been displaced by gas influx from the matrix and matrix pressure drops below the critical desorption pressure). Therefore, post-flowback analysis should properly couple flowback history, and account for secondary fracture and gas desorption effects to yield reasonable results.This paper shows how to perform a complementary flowback and post-flowback data analysis for comprehensive fracture/reservoir characterization. This complementary approach provides engineers with a tool to estimate fracture parameters (such as half length) from flowback analysis and use them as inputs for post-flowback analysis. Although a dual-porosity framework is sufficient for flowback data analysis, proper post-flowback analysis should account for both secondary fracture effects (using a triple-porosity framework) and gas desorption effects.