During a mini-frac, test fluid is pumped in a short pulse into the reservoir to create a small fracture that cuts through near- wellbore damage to establish communication with the true formation. Hydraulic fractures naturally follow the path of least resistance, thus propagating perpendicular to the formation’s minimum principal stress. After the fracture is opened, the pumps are shut down. As the downhole pressure declines, test fluid leaks off into the formation and the induced fracture closes. Pressure data can be analyzed to determine when the fracture closes. The pressure at which a hydraulic fracture closes is considered to be equivalent to the smallest principal in-situ stress of the formation.
To detect when the fracture closure occurs, BGES believes that a single unique closure event should satisfy multiple diagnostic plots or methods. Therefore, a combination of different analytical methods is used in concert to arrive at a consistent interpretation of fracture closure.
These tests can be done in open- or cased-hole completions. Open-hole tests have the risk of being impacted by packer-induced stress, but if done properly, its results can be used to estimate the maximum horizontal stress.