Estimating permeability in unconventional subterranean reservoirs using diagnostic fracture injection tests

摘要

In an example diagnostic fracture injection test (DFIT), or a “minifrac,” a fracturing fluid is pumped at a relatively constant rate and high pressure to achieve a fracture pressure of a subterranean formation. Sometime after achieving formation fracture pressure, the pump is shut off and the well is shut in, such that the pressure within the sealed portion of the well equilibrates with the pressure of the subterranean formation. As the pressure declines, the pressure of the injection fluid is monitored. This collected pressure data is then used to determine information regarding the permeability of the subterranean formation. In some implementations, a model for before closure analysis (BCA) can be used to estimate the permeability of a formation based on before closure pressure data (i.e., data collected before the fracture closure pressure is reached) based on a solution to the rigorous flow equation of fracturing fluid, which is leaking off into the formation during fracture closure.

主权项

1. A method for determining a permeability of a subterranean formation, the method comprising:
injecting a fluid through a well into a subterranean formation at an injection pressure sufficient to cause a fracture of the subterranean formation; shutting in the well after injecting the fluid; before closure of the fracture, monitoring a pressure of the fluid injected into the subterranean formation after shutting in the well to provide before closure pressure data; determining information about the permeability of the subterranean formation based on the before closure pressure data using a mathematical formula relating a measured pressure, Pi, at the time of shutting in, ti, and the measured pressure, Pn, at a later time prior to closure of the fracture, tn, the mathematical formula corresponding to a solution of a flow equation of the form:∂2⁢PD∂xD2=∂PD∂tD, where PD is pressure, xD is a spatial dimension of the fracture, and tD is time.