Effect of Well Abandonments on EOR Potential
Authors: Brashear J.P. , Biglarbigi K. , Becker A.B. , Ray R.M. 
Published: December 2007

Summary
EOR holds significant potential for producing additional oil from known reservoirs in the U.S. However. the economical application of the tertiary processes required to produce this oil relies on the use of produce this oil relies on the use of existing wells as points of reservoir access. Abandonment of these wells could substantially reduce the future recovery potential of the huge known remaining oil resource. This paper summarizes the effect of well abandonments on recovery potential by various EOR methods for more than 1,400 major fields that account for 67% of total known original oil in place (OOlP) in the U.S. The study place (OOlP) in the U.S. The study concludes that replacing existing wells (after their abandonment) would significantly increase costs and reduce U.S. EOR reserves.

Introduction
At the end of 1987, known U.S. reservoirs were estimated to contain 513 billion bbl of OOIP. of this resource, 145 billion bbl has already been produced. Another 27 billion bbl remains as proved reserves, oil that can be economically recovered at current oil prices with current technology (Fig. 1). The prices with current technology (Fig. 1). The remaining two-thirds of the known resource, more than 340 billion bbl, cannot be economically produced with currently available technology. This oil is trapped or bypassed by conventional recovery techniques owing to reservoir heterogeneities and unfavorable rock and fluid properties within the reservoir. The remaining resource falls into two categories:unrecovered mobile oil that could, if contacted, be recovered through natural reservoir forces or displaced by water and recovered through the use of improved primary and secondary recovery techniques, such as advanced waterflooding and infill drilling, andimmobile oil that is residual to secondary recovery processes and can be recovered only by use of tertiary EOR processes, such as thermal recovery, miscible gas injection, or chemical flooding. Even with the technological and eco nomic limitations of current advanced secondary and tertiary methods, their widescale implementation could significantly increase U.S. proved oil reserves.
A 1984 Natl. Petroleum Council (NPC)study estimated that up to 14.5 billion bbl of oil could be produced though tertiary recovery processes at a $30/bbl oil price. This estimate processes at a $30/bbl oil price. This estimate includes nearly 4.0 billion bbl of incremental reserves from ongoing thermal flooding activities in California. Future EOR projects clearly could boost U.S. production, or slow its rate of decline, for decades. The viability of these projects, however, is treated by recent trends in well abandonments. Low oil prices have accelerated the abandonment of stripper wells, and increasingly stringent environmental regulations have increased the costs of regulatory compliance while imposing potential future liabilities. potential future liabilities. The NPC estimates of incremental EOR reserves were based on the assumption that all existing wells penetrating candidate reservoirs could be fully utilized in future projects; only a small number of new wells projects; only a small number of new wells would be required to adjust the injection-pattern geometry in EOR floods. On the basis of these assumptions, most of the EOR project investment costs modeled by the project investment costs modeled by the NPC were for the purchase and installation of required injection/processing facilities and the upgrading and conversion of existing injection and production wells. This study assesses the effect of well abandonments on EOR reserve estimates on the basis of the additional costs of replacing existing wells. other additional costs for reactivating project areas, such as legal fees and bonus payments necessary to reacquire leases or to re-form production units alter their abandonment, are not considered. Therefore, this analysis can be interpreted as an optimistic assessment of the full effect of resource abandonment on U.S. EOR potential. potential.

Historical and Current Trends
The profitability of new EOR projects strongly depends on maintaining access to the immobile oil resource through existing wells. To the extent that existing wells are abandoned and are not available for use in new tertiary recovery projects, future EOR reserves in the U.S. could be reduced. No previous works, however, have addressed previous works, however, have addressed the effect of these abandonments on the future of domestic oil recovery. Throughout the U.S., declining production rates combined with low oil prices production rates combined with low oil prices threaten the economic viability of large numbers of wells and leases. After more than 125 years of the most extensive exploration and production in the world, the U.S. resource has matured. This maturation, shown in Fig.2, has been reflected in steady declines in production and reserves in the Lower 48. Year-end Lower 48 crude oil production in 1970 was reported as 3.4 production in 1970 was reported as 3.4 billion bbl and declined 39% to 2.1 billion bbl in 1989. Similarly, Lower 48 crude oil reserves decreased 31% to 19.8 billion bbl in 1989. As the resource has declined, the proportion of stripper wells (wells that proportion of stripper wells (wells that produce less than 10 barrels per day) produce less than 10 barrels per day) has grown to 73% of all producing wells. Stripper wells contribute about 19% of Lower 48 total crude oil production.