Since no other single expenditure has a greater impact on a tight reservoir's profitability than a hydraulic fracture treatment, optimal job size selection is imperative. However, the actual reservoir deliverability improvement is usually quite different from the forecasted results. Poor fracturing results are primarily attributed to poor reservoir characterization and reduction of the in-situ fracture conductivity over the laboratory estimates. To estimate in-situ fracture conductivity, and subsequently enhance the fracturing job design, a historical correlation between job size and wellbore improvement was established. This correlation was based on the post-fracture evaluation of 70 wells in the Arkoma basin.

Matching our data with McGuire and Sikora's solution, the retained fracture conductivity ranged from 20% to 50% of laboratory estimates depending on the aggressiveness of proppant placement. The influence of a different thickness in propped height and net pay height was factored into the optimal job sizing process. When modified for this difference, the PKN modeled FCD was consistent with our field observation for low FCD treatments. A field estimate of the optimal job size was also developed from the historical correlation using a marginal benefit and marginal cost model. Ease of application and historical accuracy are the two major strengths of this approach.

Greater cost effectiveness was achieved when these design considerations were incorporated into the field practice in the Arkoma basin. Since this study surveyed the diverse reservoirs and depositional environments within the Pennsylvanian age, we feel the approach will be applicable in similar areas.

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