The oil and gas industry has been successful in its use of trial-and-error as the main technique for enhancing the productivity of fracturing treatments in horizontal wells. The lower fracturing costs of the last three years have provided the impetus for moving in the direction of more aggressive treatments; much larger volumes of fluid and proppant, longer horizontal reaches and shorter spacing between adjacent fractures. In general, these changes are claimed to have improved the productivity of fractured horizontal wells, at least in the short term for which data has been available.
The justification for these changes requires assuming a different model of fracture propagation than is often assumed by the fracturing community. Closer examination of these treatments indicates that they implicitly assume a more planar fracture shape. Some of the existing data on pressure interaction between offset wells while fracturing shows incidents of fracture shadowing as well as frac/frac intersections. At times the observed data indicates low effective fracture conductivities, which is in-line with the practice of using more proppant. The relatively consistent fracture orientation within a single well and in multiple offset wells indicates larger difference between the two horizontal principal stresses than usually assumed within the fracturing technical community. This condition is needed for the success of the more aggressive treatments.
On the negative side, aggressive well and fracture spacing can increase fracture length and the likelihood of interference between fractures in adjacent wells. Taken too far, this can have significant impact on future reservoir development, including damaging the existing fractures, and production re-distribution between offset wells.