Abstract

There is no doubt that improved frac designs can increase production rates from many reservoirs. However, do these changes merely accelerate recovery, or is incremental production gained by changing the fracture design?

Results from field trials are often published within a year (or even less!) of the initial design changes, and EUR projections are required to forecast the long-term economic impact. This paper will document a re-examination of three tight gas case studies published in the past ten years to determine whether recovery projections were accurate. Included are a review of field studies performed in the East Texas Haynesville Lime, the West Texas Canyon Sand, and the East Texas Cotton Valley-Taylor Sand. The original studies in these tight gas formations were specifically performed to assess the impact of increased fracture conductivity on production. In all cases, the initial analyses documented that increasing conductivity appeared to increase production and recovery.

By revisiting these case studies using extended production data, a more rigorous determination of recovery and associated economics will illustrate whether recoverable reserves are increased from tight gas reservoirs with careful modification of fracture designs. This paper will speculate on the mechanisms that may allow incremental reserves to be captured from some reservoirs, and will evaluate the uncertainty of reserve forecasts constructed from less than one year of production data. This summary should be of interest to any engineer who must estimate the recovery impact of completion changes when only limited production data is available.

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