Abstract
The objective of this study was to determine the remaining waterflood potential for a deep, thin-bed sandstone reservoir with an existing waterflood and to propose a plan to maximize the economics of future field performance. Little published information is available examining the waterflood potential of thin-bed sandstones. In addition, determining how much capital to allocate to increase secondary recovery depends on remaining reserves, an uncertain volume when differing calculation methods yield different values.
My study of the West Verden Hoxbar Unit in Caddo County, Oklahoma led to the conclusion that waterflooding this and similar thin-bed sandstones with 320-acre patterns can achieve secondary recovery factors of 10 to 25%. Downspacing these fields is not necessary because high vertical sweep efficiency allows for effective floods on this spacing. However, 320-acre pattern spacing is wide enough that areal sweep efficiency becomes the primary concern when attempting to increase secondary recovery volumes after breakthrough has occurred in existing flood patterns. The solution is to realign existing patterns by converting selected current producers to injectors, which allows for the production of hydrocarbons not initially contacted by the waterflood.
To determine whether this development plan is appropriate for a field, I recommend a workflow consisting primarily of decline curve and oil cut v. cumulative oil plot analysis, oil recovery v. water input plot interpretation and pattern analysis.
The dominant benefit of this approach to increasing recovery is that it does not require drilling new wells to increase production. Conversions can typically be implemented for 1/10 the cost of drilling a new well. My recommendations are currently being implemented in the West Verden Hoxbar Unit because my studies show that the conversions are economic at oil prices as low as $29/barrel, pay for themselves in less than 2 years, and extend the productive life of the field by over 10 years.
