Operators working with multiple stacked-pay reservoirs are challenged to optimize economic returns through their completion designs - not only in regards to horizontal well spacing, but also with vertical well spacing. Many of the popular Texas and New Mexico Wolfcamp formation sections exceed 1,000 feet in thickness and contain multiple hydrocarbon-rich benches. These benches and associated strata are complex mixtures of heterogenic geological factors such as weak/strong structural interfaces between facies, open/healed natural fractures, unpredictable fluid and pressure regimes, along with other lithological variables. Companies wrestle with the optimization of maximum hydrocarbon recovery within ever-present economic constraints when developing reservoir targeting strategies.
This case study used multiple solid, oil-soluble tracers (OSTs) as an aid in reservoir characterization to determine optimal landing zones in the two unique Wolfcamp formations. This was accomplished by monitoring OST recovery data produced from grouping frac stages and reservoir zones over a 435 sampling day period. The two wells in this case study were intentionally drilled highly toe-up in order to cross all the potentially productive areas in two separate Wolfcamp benches; all stages were completed with the same stimulation design.
The dynamics of the OST recovery provided insight into the variability of reservoir productivity within the Wolfcamp. Particular layers in the two wells exhibited initially high but transient OST recoveries, while other zones produced OSTs longer and more consistently. Using granular level tracer data in conjunction with other geoscience information, the operator was able to identify the formation layers having the highest potential for optimal production economics. This new methodology not only provided single-well placement optimization, but also important insights for future completions.