5.: Hydraulic Fractures and “Pseudomatrix” Injection

In some cases where there are concerns about the impacts that ongoing fractured injection might have, there might be options to deliver some of the benefits of fractured injection without suffering any associated sweep problems.

One option is to hydraulically fracture the wells. In this way, it is possible to design the fracture so that the subsequent injectivity is improved because of the increased available leakoff area. This option is very commonly used in the waterflooding of lower-permeability reservoirs. Hydraulic fractures can be used to stretch waterflood patterns in low-permeability fields (Khasanov et al. 2009). This technique is beginning to enable waterflood to be deployed in very tight reservoirs. Waterflood is taking place using hydraulic fractures in the North Wasson Clearfork Unit in the Permian Basin, in the US, where average permeabilities are only 0.5 md (Wagia-Alla et al. 2018). Production normally uses transverse fractures in these reservoirs but, because this would be developed using waterflood, longitudinal fractures were selected for sweep purposes. This example uses horizontal wells, but an application in China where a similar technique was deployed in a 1-md reservoir used vertical wells (Wang et al. 2017).