Field experience and numerical investigations of minifrac tests with flowback in low-permeability formations

In this study,flowback-assisted minifrac tests were conducted in low-permeability shale and salt formations to measure the in situ stress.An injection/flowback testing protocol was implemented in each test to achieve accuracy and efficiency.Accurate and efficient injection/flowback testing is very important,given the impermeable nature of these formations and the need to complete each test as quickly as possible.Each flowback cycle yields a distinct and repeatable fracture closure signature,simplifying the interpretation of the fracture closure pressure.The objective of this paper is to share our field experience and to present a numerical analysis of the flowback test pressure responses,fracture closure behaviors,and fracture closure diagnostic methods.Examples from open-hole and casedhole minifrac tests are used to demonstrate site operation procedures.Then,two numerical models are presented for simulating the fracture closure behavior during a flowback test.Field evidence is provided to demonstrate that the fracture closure pressures from the flowback tests are identical to those from tests without flowback.The fracture closure diagnostic methods for flowback tests are discussed,and it is found that the G-function diagnostic method yields a distinct fracture closure signal during the flowback tests.This study is intended to provide additional insights regarding flowback tests by sharing our successes,experience,and knowledge,thereby benefiting the industry.