Optimization of Stimulation Treatments in the Wamsutter (Almond) Formation by Means of Prefracture Impulse Diagnostic Tests

摘要

The Wamsutter (Almond) formation in southwest Wyoming is a tight gas reservoir in the eastern part of the Greater Green River Basin (GGRB). The Almond formation is generally encountered between depths of 8,500 and 10,500 feet with reservoir pressures varying from initial conditions (0.54-0.58 psi/ft) in the Lower Almond to varying stages of pressure depletion in the Upper Almond. The Almond interval is generally completed via massive hydraulic fracture stimulation down casing with a series of treatments targeting the Lower, Main and Upper Almond intervals. These zones are subsequently commingled for production. In the absence of reservoir properties such as in-situ reservoir permeability, reservoir pressure, and closure stress, it has been difficult to optimize the stimulation treatments on a zonal basis. To identify these reservoir characteristics, pre-fracture impulse injection testing has been performed in each interval. These simple, easy to perform transient tests have aided in the interpretation of the key reservoir parameters. This work presents data from eleven wells in the Wamsutter field and describes the methodology used to optimize the stimulation treatments. Reservoir properties obtained from the impulse tests helped eliminate the addition of nitrogen to the fracturing fluid, which had been routinely included to aid fracture clean-up after fracture stimulation. This design change has led to more effective fracture stimulation treatments yielding higher gas production rates while significantly reducing completion costs. Production from wells stimulated with the modified design is compared to production from wells that were stimulated without the benefit of reservoir properties obtained from the pre-fracture impulse tests.