Initiation of a secondary hydraulic fracture and its interaction with the primary fracture

Abstract

Laboratory and field experiments have shown that secondary fracture treatment along a different direction to the primary hydraulic fracture can increase the recovery of gas from tight sands. Success of a restimulation treatment (secondary fracture treatment) is, however, highly dependent on transient stress distribution around the well. In this paper a numerical poroelastic reservoir model is used to provide a more realistic picture of stress field around a stimulated well during post-fracture production. Initiation of a re-oriented hydraulic fracture and its interaction with the primary hydraulic fracture are also studied using a wellbore re-pressurization model that includes a poroelastic formation, a wellbore and a pair of finite conductive hydraulic fractures. Numerical results have shown that during post-fracture production the directions of maximum and minimum horizontal stresses are reversed within a large area around the wellbore and the hydraulic fractures. We have also shown that relatively small areas exist at the wellbore wall where the original directions of horizontal principal stresses remain unchanged. It is shown that the presence of these small areas could act against initiation of a secondary hydraulic fracture along the most desired directions in terms of recovery enhancement. This study also shows that oriented perforations prior to refracture treatment help initiate secondary fractures in a preferred direction before the primary hydraulic fractures start propagation during re-pressurisation of the wellbore.