Fracability Evaluation Method for Tight Sandstone Oil Reservoirs

As typical low-permeability unconventional fossil resources, tight sandstone oil cannot be exploited economically without effective hydraulic fracturing. Fracability is a term commonly used as a decision indicator to select candidate layers for hydraulic fracturing in unconventional reservoirs. In this paper, because of the objective of fracturing treatment in unconventional reservoirs, fracability is defined as the ease of obtaining a complex hydraulic fracture network (HFN) and a large stimulation reservoir volume (SRV) under the same fracturing technology and engineering parameters. The HFN probability index (PIHFN) and the SRV probability index (PISRV) are introduced to characterize the ease of an unconventional reservoir to obtain a complex HFN and a large SRV with fracturing treatment, respectively. Reservoirs with higher PIHFN imply that a more complex HFN may be created with fracturing treatment. Similarly, a reservoir with higher PISRV is likely to form a larger SRV. A new fracability index (FI) model is developed by integrating the PIHFN and PISRV. This FI model considers that a good fracturing candidate not only has a high PIHFN but also requires a high PISRV. Brittleness, fracture toughness, natural fracture and in situ stresses as the key influencing factors of fracability are considered by the new FI model. Three tight sandstone oil wells were studied to validate the accuracy and feasibility of the FI model and describe the process of screening fracturing candidates with the new method.