Dynamic Reservoir Characterization using Injection Pressure Data from Brine Disposal Operations

Srikanta Mishra and Mark Kelley
Battelle Memorial Institute, Columbus, OH, [email protected]

Brine disposal wells used to dispose waste water from drilling, production and hydraulic fracturing are typically developed based on minimal geologic and reservoir characterization data. Injection pressures and volumes are reported on a monthly basis per regulatory requirements, but are not commonly analyzed to extract insights about reservoir behavior. However, recent increase in demand and concerns for seismic activity related to brine disposal operations has reinforced the importance of understanding the geologic and reservoir characteristics at these locations. To that end, this paper presents a strategy for characterizing the injection reservoir using pressure buildup data during injection, as well as pressure falloff data from intervening shut-in periods.

Using an analytical well-test simulator, we simulate pressure response following brine injection into a variety of reservoir geometries: (a) homogeneous high (low) permeability formation with no boundaries; (b) composite reservoir with a high (low) permeability inner zone and low (high) permeability outer zone, and (c) high (low) permeability formation with a sealing fault. The rate history during the injection period is assumed to be variable, as is commonly the case with injection operations. Pressure buildup at the end of 1-year of injection and 1-week of shut-in; and transient pressure response during the shut-in period are taken to be key performance indicators. From these simulations, the shut-in pressure derivative (Horner slope) was determined to be useful for assessing reservoir conditions (i.e., homogeneous, composite) and detecting the presence of nearby boundaries (permeable and impermeable). However, the duration of the shut-in period needs to be consistent with the properties of the reservoir and the area of the reservoir that will be used to store the brine or these features will not be detected.

Key findings from this study are: (1) pressure data from the shut-in period can provide useful diagnostic signatures for various reservoir configurations and help identify potential barriers to flow, (2) transient pressure analysis enables more dynamic reservoir characterization as compared to wireline tools and short-duration pre-injection testing, (3) falloff testing is more amenable to interpretation than injection data with variables pressures and rates reported as monthly averaged values. Routine analysis of injection pressure data will benefit operators and regulators in determining commercial viability (i.e., injection potential, well configuration planning, economic capacity, etc.) of brine disposal facilities and ensuring their safe operation.

AAPG Search and Discovery Article #90154©2012 AAPG Eastern Section Meeting, Cleveland, Ohio, 22-26 September 2012