Sufficient production and fracture mapping evidence across North America is now available to clearly demonstrate that pairs of delineation and development wells often underperform when there is substantial production time (months or years) between the completions of the two wells. The relative degree of impact on hydrocarbon extraction per acre varies from one play or formation to another, but the phenomena is generally attributed to asymmetric induced fracturing from the development (child) well into the previously partially drained and lower static pressure delineation (parent) well reservoir volume. This paper briefly discusses two solutions that have been employed to minimize the negative fiscal ramifications and improve recovery.
Rigorous 3D unstructured grid reservoir modeling can assist in the quantification of the phenomena; however, options for mitigating the problem for cases where the impact is extreme are typically limited. Synthetic history matching and forward modeling were performed with a grid-based numerical simulator that mimicked a series of asymmetric oblique fractures interacting with a drained reservoir volume, comparing acceleration of reserve recovery and total recovered reserves with a similar case involving symmetric fracturing. Two scenarios for preventing extreme asymmetric fracturing are discussed. These included dramatic shortening of the time between completions, and performing pressure sink mitigation (PSM) via refracturing of the delineation wellbore.
It is shown that the asymmetric fracturing into drained volumes can materially impact reserves and rate of recovery if the acreage position of a given project is substantial. It is demonstrated that the overall stimulated reservoir system permeability, the degree of permeability contrast between reservoir layers, and the degree of asymmetry are all factors that have an impact on the degree to which the long-term time between completions affects recovery of hydrocarbons over and above simple volumetric depletion.
Integration of rigorous 3D reservoir modeling and far-field fracture mapping have established that the negative ramifications of extreme induced fracture asymmetry can be overcome with careful application of drilling and completion (D&C) timing and offset drainage pressure management process.