Shale resource plays often present formidable reservoir management challenges, particularly with regard to capital utilization and allocation. In spite of significant efforts to measure and analyze key reservoir and completion data, uncertainty typically remains in the physical characteristics of the stimulated reservoir volume (SRV) accessed by hydraulic fracturing, namely: shale permeability, fracture spacing, SRV spatial dimensions, and gas-in-place.
In this study, well performance histories of several hundred wells spanning the Haynesville, Woodford, Barnett, Horn River, Marcellus, Fayetteville and Montney shale plays were investigated with a common and consistent analytical framework that determined: a) a well productivity measure during infinite-acting linear flow, b) completion pressure losses (between sandface and bottomhole), and c) apparent original-gas-in-place in the SRV. Parameters determined from the analyses are key indicators of the combined result of reservoir quality and hydraulic fracture performance. Results of this multi-well cross-play study provide information about both inter- and intra-play variability and commonality.
A large proportion of the wells (85%) showed prolonged periods of linear transient flow, indicative of low matrix permeabilities. Wells of higher productivities tended to go into depletion flow earlier, which could be consistent with either high matrix permeability or large fracture surface areas that are close together (complexity). Completion pressure drops were not observed as the dominant productivity-loss mechanism. Productivity of wells during infinite-acting flow normalized by the total mass of proppant used in each well, an SRV creation efficiency, and the original-gas-in-place in the SRV for all wells in this study showed log-normal distributions. The 100-day flow efficiency of the completions in these wells showed a truncated normal distribution.
Recognizing the variability in the reservoir characteristics of the studied shale plays, and SRV's that were outcomes of diverse completion practices, the observed predictability in key well performance characteristics is remarkable. The distributions presented in this paper can be used to improve well performance predictability, help identify sweet spots for drilling, establish relatively narrow ranges of a priori well performance characteristics (therefore reducing uncertainty at undeveloped well locations), improve fracturing practices, and provide support for decisions of capital allocation.