The estimation of incremental oil or gas recovery from infill drilling is essential to substantiate the recommendation to drill development wells or to evaluate the benefit of reducing the well spacing in a developed field. The purpose of this paper is to discuss four different techniques that can be used to quantify incremental oil recovery and accelerated production from infill drilling. These methods are summarized below.
A reservoir continuity model illustrates the concept that infil1 drilling improves the continuity between wells, this in turn will improve the reservoir sweep efficiency and ultimate recovery.
A plot of water-oil ratio on semi log scale versus cumulative oil production on linear scale is used to demonstrate the incremental oil recovered from infill drilling.
Decline curve analysis is used to estimate the incremental recovery and accelerated production, and the interference between infill and offset wells.
A reservoir simulation model is used to predict production forecast for the infill wells, and to estimate the incremental recovery versus the accelerated production from infill drilling.
Infill drilling can increase ultimate gas or oil recovery but the incremental recovery from infill drilling varies for each pool because of difference in reservoir heterogeneity and fluid properties1–3. Consequently, determination of incremental recovery from infill drilling is a challenging task in reservoir study. A further complication is to quantify and differentiate the incremental recovery from the accelerated production. The benefits of incremental recovery and accelerated production from infi11 drilling have been extensively debated and documented4,5.
This paper presents four methods that can be applied to estimate or evaluate both incremental recovery and accelerated production from infill drilling, however no one method is necessarily more accurate than another. Very often, the selection of a specific method depends on the availability of the reservoir performance data and the time constraint. If possible, all four methods should be used to determine incremental recovery. This would enhance the confidence of the results calculated by each method and to complement each other.
To determine or evaluate incremental recovery from infill drilling, the applications of reservoir continuity model, water-oil ratioplot, decline curve analysis. and numerical simulation model are presented based on the field performance data and the experience that we have gained in our reservoir studies in Alberta.
Numerous reservoir studies have revealed that, in a continuous porous reservoir, drainage of fluids can occur effectively over large area in formation of either low or high permeability. The major factor that appears to restrict the drainage area by a well is the lack of continuity within the formation due to heterogeneity. The theory and case history indicating that infill drilling will increase reservoir continuity and hence improve waterflood pattern conformance in heterogeneous West Texas carbonate reservoirs have been published in literature 6–11.
Reservoir continuity is defined as the portion of the net pay that can be correlated and onnected between two or more well s at a particular well spacing.
