Unified Fracture Design for very low permeability reservoirs

Unified Fracture Design (UFD) is a methodology for the design of optimal hydraulic fracturing treatments to maximize well performance. Many successful applications of UFD have been demonstrated for reservoirs with low to high permeability. However, UFD has not been systematically applied to reservoirs with very low (nanodarcy) permeability, such as shales. For such reservoirs, massive hydraulic fracturing combined with horizontal drilling has enabled the production of significant amounts of hydrocarbons in recent years. Yet a method for the design of optimal hydraulic fracture treatments for these reservoirs is currently lacking, with present practice relying mainly on rules of thumb and trial and error. This paper fills this gap by developing a design methodology through extension of UFD that addresses two important elements: (a) nanodarcy permeability reservoirs, and (b) fractures with highly elongated drainage areas, that are necessary because of the extremely small reservoir permeability. Simple explicit functions are developed that can be used for efficient computation of optimal fracture dimensions and the productivity index for large values of Proppant Number and highly elongated drainage area around each fracture. A case study is presented to demonstrate how the developed UFD extension can be used in practice and to illustrate the qualitative differences between standard UFD and the developed extension.