Determining Injection Pressure Limits With Wireline Testing Inputs

A matter of concern in most secondary recovery projects is control of the movement of injected fluids. If the injection pressure exceeds the fracture gradient of the confining layers of rock, the injected fluids will not be optimally placed. Historically, operators have seen evidence of exceeding fracture gradients in pay zones using Hall plots, fall off tests, square root of time plots or step rate tests. All these methods require fracture stimulation of the rock and though they describe the pay zone stresses adequately, they lack data on the boundary rock. Tracer surveys can tell when the fluids have migrated out of zone. Unfortunately, this data is obtained after the fact. Determining the injection pressure limits prior to fracturing out of zone is preferred. With developments in in-situ stress measurements, this data is now available in a timely manner. The methodology proposed is to determine a continuous hydraulic fracture gradient in the wellbore using full wave sonic data and formation pressure data. This has been accomplished on Over 700 producing wells since 1984 to control the hydraulic fracture treatment. Recently, this technology has been expanded to include water injection wells to control the injection process. A discussion of the methodology used follows along with a field example.