The first of the projects was named “Strategic Studies of ROZs in the Permian Basin – RPSEA Residual Oil Zone (ROZ)”
Early pre-project work suggested that the northern and eastern side of the Delaware Basin within the Permian Basin was an excellent candidate for ROZ identification, data gathering and ROZ fairway modeling. The ROZ personnel Team developed and utilized several working theories to describe the indirect or anecdotal evidence indicating the presence of ROZs in this region. In addition, observations were enlisted from the wealth of experienced geologists with experience in the Permian Basin through both personal interactions and through a more formal ROZ symposium with over 100 persons present (Oct 2009 – see this paper).
The initial stages of the current effort confirmed that this one particular region of the Permian Basin was indeed an excellent candidate for the data collection and hydrological modeling work. The exhaustive data gathering effort was initiated in attempt to spatially define and characterize the “fairway” of flushing which led to the development of a San Andres formation ROZ. The six counties that have been involved in the data gathering, Pecos, Loving, Ward, Winkler (all in west Texas) and in Lea and Eddy Counties in New Mexico include the fairway ROZ targets. Wells in near proximity and those actually penetrating the ROZ were identified, water sample analysis located, scout cards reviewed, coring results documented, drill stem test data assimilated, and, from the wealth of acquired data, the fairway(s) were outlined and mapped (Figure 1). All of the data have been placed into a large database (inclusive of all reviewed oil and water wells) and made part of the unsorted database but, for wells outside of ten miles from the fairway, eliminated for a project specific data base. Interval thickness, porosity and permeability data from logs, core and drill stem tests form the key data set for setting up the ROZ fluid and rock property data and hydrological model input. The computer model under development was designed in an attempt to illustrate the validity of the observed subsurface conditions and provide features of ROZs that could be tested with new wells and cores. Parametric variations of the model will be performed especially on the “choked” exit of the flush water in attempts to find the best recharge/discharge model for explaining the mechanics for the lateral flushing which created the ROZ.
Several companies are showing interest in validating the theories and provided verification data prior to the project reporting phase in late summer 2011. Numerous technology transfer requests (Appendix 1) were granted for presentations by project personnel. ROZ interest continues to grow. The interests from other parts of the Permian Basin, other Basins and around the world has been strong. To cite examples, a ROZ study was chartered by the Enhanced Oil Recovery Institute in the Big Horn Basin (Wy) and work accomplished by project personnel set the stage for a similar study in the Williston and Powder River Basins (WY, SD, ND, and MT), conversations are on-going with professionals in Asia and countries in the Arabian Gulf.
Through the developing relationships with CO2 flood operators, the Team has gathered a few ROZ water samples and we have conducted some preliminary water chemistry testing which suggests opportunity for identification of anaerobic microbial processes at work and possible assistance in ROZ development and comparison of ROZ properties in other parts of the Permian Basin, U.S., and Worldwide. The Team has also identified a characteristic log character that would further confirm the presence of the shelf parallel, lateral flushing process and a late-stage “pervasive” dolomitization that led to enhanced oil wetting and greater oil saturation targets for EOR. A real bonus of the model work could be to ultimately confirm this lateral flushing process as the late-stage, pervasive dolomitization phase of reservoir development in contrast to the more widely accepted basin dewatering, updip and shelf perpendicular dolomitization.
The ROZ Team clearly believes the results of this RPSEA I study may not only pertain to the Delaware Basin shelf region but has lead to a greater understanding of the prolific dolomite reservoirs throughout the Permian Basin. There is also evidence that the work, in a more specific sense, has lead to a privately funded demonstration project in the Central Basin Platform area where the theories and model are being commercially tested through a pilot project using CO2 EOR techniques.