Zero Net Gas Production: An EOR Strategy for Pads
Applications for the liquids-rich portion of the Montney
Cyclic gas injection (huff-and-puff) in hydraulically fractured wells has been successfully applied, at single well or pad level, as an EOR method in tight unconventional basins such as Permian and Eagle Ford. Since 2014, a considerable amount of literature and research has been devoted to feasibility, implementation and optimization of gas huff-and-puff in fractured unconventionals. Most of these studies have been devoted to oil reservoirs and few publications have addressed gas condensates. Furthermore, to the authors’ knowledge, all the publications addressing the suitability of huff-and-puff EOR in the Montney are focused on individual well studies and none consider the performance of the process on a pad-level basis. This study attempts to study the application of huff-and-puff on a typical, stacked Montney pad and propose alternatives to increase recovery and improve the economics of the process.
One of the drawbacks of cyclic processes is the unproductive time that is dedicated to injection and soaking. In this paper we evaluate the feasibility of implementing a sequential huff-and-puff strategy where wells in a pad convert to injector and producers sequentially to avoid unproductive time. The produced gas is reinjected back into the reservoir to eliminate the need to bring an external EOR agent, while taking advantage of the heavier fractions still left in the stream. Since compression is one of the highest costs associated with huff-and-puff EOR in unconventionals, injecting in one well at a time with a compressor that is continuously active will help in reducing the CAPEX significantly.
To perform this study, publicly available data was used to construct a geomodel of typical reservoir in the liquids-rich portion of Montney. Geomechanical and natural fracture parameters were incorporated into the model. A 4-well pad was considered, and typical completion and pumping schedules were used to predict hydraulic fracture propagation and geometries representative of typical stimulated volumes in this play. A compositional numerical reservoir simulator was then used to forecast liquid recovery under different huff-and-puff scenarios.
The results of this study show that under favorable stimulation conditions (planar hydraulic fractures with minimum frac-to-frac interaction), applying huff-and-puff in a sequential schedule under a zero net gas production strategy, can significantly improve pad condensate recovery through re-vaporization and frac-to-frac displacement mechanism. Cash flow projections of the zero net gas production huff-and-puff scenario indicate that such a strategy yields a better economic outlook when compared to the one obtained under primary depletion; this is true when the oil price is higher than $30/bbl.
The implementation of the scenarios studied in this paper require a proper understanding of the hydraulic fracture geometry. If there is a greater degree of uncertainty on the hydraulic fracture characteristics, or the fractures are not entirely planar and there is increased interaction between them, it might be more advantageous to apply a pad-level injection/production huff-and-puff strategy.