Water disposal is a critical component of daily operations in unconventional and some conventional oil and gas fields. Holistic management of disposal reservoirs requires assessment of the fillup volume to drive reservoir management. Traditional material balance, pressure transient analysis, and static volumetrics have been the only ways to estimate the fillup volume. This paper presents a new methodology that uses flowing data, disposal rates and pressures, to determine a fillup volume by applying flowing material balance theory originally developed for producing wells. This analytical method estimates average reservoir pressure as a function of cumulative water injection. Fillup is found by extrapolating the linear trend of reservoir pressure versus cumulative water injected. The advantage of this technique is fillup volume is estimated with flowing data that is captured as part of daily surveillance requiring no incremental acquisition costs. In this paper, the methodology is applied to synthetic examples. Additionally, its application is demonstrated in three case studies for basins with different geological settings. One is an uneconomic gas reservoir that is used for saltwater disposal, the other is a well producing from a gas reservoir that is converted from a producer to water disposal after depletion, and the last is a well in a disposal reservoir that is carbonate-rich. Results demonstrate the flowing material balance accurately predicts average reservoir pressure when compared to synthetic water disposal examples. When compared to traditional material balance, the flowing material balance yields the same fillup assessment in a more cost-effective way. The application of this method has helped asset teams decide to add additional perforations to increase fillup volumes, perform workovers to increase injectivity, drill additional disposal wells for additional capacity, reduce costs associated with collecting static shut in pressures, and apply reservoir management to saltwater disposal reservoirs.
Field water production is a focus area for the oil and gas industry. Associated and flow back water management strategies include recycling for field operations like hydraulic fracturing, disposal via surface discharge after treatment, or disposal via underground injection. However, water disposal wells remain the most cost-effective option for wastewater disposal as minimal pretreatment is needed (Gay, Fletcher, Meyer, et al 2012).
