BP has developed a novel, low cost method of measuring reservoir pressure in unconventional gas reservoirs. This new approach (patent-pending) measures the pressure of low permeability gas reservoirs by a series of small injection steps prior to hydraulic fracture stimulation. The analysis is completed by plotting injection and rate data in a specialized form of Darcy's flow equation. The method has been successfully tested in the Almond Formation in the Wamsutter Field, WY. This paper will illustrate numerical simulation results used in the preplanning of the field trial plus the actual results from the field trial itself.
Understanding ranges of reservoir depletion is essential in optimizing field development within tight gas plays. Unfortunately, determining reservoir pressure in low permeability reservoirs is difficult due the long shut-in times required for conventional pressure transient analysis. Completion designs, modeling studies and future field development decisions are all improved with better knowledge of current and historical reservoir pressures.
The results from the reservoir simulation suggested that the method could be useful in estimating reservoir pressure for tight (<0.1 md) gas reservoirs. When applied on the first field trial on an over-pressured 0.001 md reservoir, the method measured reservoir pressure in an hour compared to the multiple days required for a diagnostic fracture injection test (DFIT).
The difficulty and expense of obtaining reservoir pressure in tight formations greatly restricts efforts to optimize spacing and completion efficiencies. Since large numbers of wells are often required for tight gas development, even small inefficiencies can be costly. The method described in this paper can be applied at minimal cost and performed in a short time frame. This opens up the possibility of obtaining individual zone pressures on multi-zone completions even during ongoing frac operations. Ultimately, this technique could allow for a robust dataset of reservoir pressures underpinning optimized depletion plans and completion strategies.