The profitable conversion of off pattern water injectors to production wells is possible in CO2 floods. An initial water production period often precedes the breakthrough of oil into such injector-to-producer (ITP) conversions. At the Wasson (San Andres) Denver Unit in West Texas, time to economic oil production and initial economic oil production rates may be estimated by simulation or analog methods. Performance data from more than 25 wells is discussed in this paper.
An irregular injection pattern, established during waterflooding of the Denver Unit, is inappropriate for a CO2 flood where the high cost of the EOR injectant requires its effective use in maximizing recovery. In developing regular inverted nine-spot CO2 flood patterns prior to CO2 startup, many waterflood injectors were temporarily abandoned because they were situated in pattern producer locations. Regularization of the CO2 flood patterns by converting former water injectors to oil producers was desired to enhance the sweep efficiency.
When CO2 is injected into the reservoir at miscible pressures, it mobilizes waterflood residual oil trapped by oil-water relative permeability effects. Oil can then be transported through water swept regions into former water injectors. Thus ITP conversions are technically feasible.
Although oil almost certainly will flow into the ITP wells, the operator must answer the economic questions of when to convert the wells and how much oil it will produce. At the Denver Unit both simulation and analog methods have been employed with success to answer these questions.
The Denver (San Andres) Unit is one of the world's largest CO2 enhanced oil recovery (EOR) projects.