This paper covers a case study in the Denver-Julesburg (DJ) Basin that reveals stage lengths can be dynamically varied when wells are tightly spaced to optimize pad drainage and completion cost in homogeneous rock strata. Alternating stage designs in offset wells can support increased stage lengths up to 6x standard (exceeding 1,000 ft) and still treat and produce as uniformly as smaller stages, due to the cooperative effect of the overlapping fracture network created by neighboring infill wells. These findings were corroborated by fiber optic data acquired during frac (cross-well strain) and post-flowback production monitoring and interference testing. We also observed Formations within damage zones altered from faults can affect drainage results.
Differing stage lengths (X, 2X, 3X and 6X) were trialed in three wells in a six well section. Fiber optic diagnostics were acquired during frac for cross-well strain evaluation and 60 days post-flowback for production monitoring and interference testing. Locations and extent of fracture interactions were observed during the fracturing process, and later compared to the production and interference testing results after flowback.
The post-completion diagnostics corroborated the during frac cross-well strain data. Interference testing reveals communication as well as unique geological features in the areas identified by the cross-well strain data. There is little if any difference in cross-well strain or production behavior of standard-length X stages offset by X stage lengths and X offset by 2X or 3X stage lengths. Performance of the 3X and 6X stages is nearly identical to the X stage lengths, in both production and interference from a uniformity and production volume.
When wells are known to interfere or communicate, completion designs can be modified dynamically to work with overlapping stage designs, optimizing completion costs without sacrificing treatment uniformity nor production. Stage lengths of offset wells, depending on the play and geologic structure, may be dramatically larger than previously thought when offset against smaller stages, while still allowing for sufficient reservoir access and drainage, leading to reduced pad development time.