08123-19

Primary Performer
The University of Texas of the Permian Basin

Additional Participants
Chevron Corporation
Yates Petroleum
Legado Resources

Abstract
The Permian Basin (PB) region of the U.S. has been noted as having very thick intervals of residual oil zones (~200-300 feet thick) beneath the oil/water contacts. Some of these ROZ zones in the largest of the San Andres Formation fields have been found to contain over a billion barrels of oil in place but at an average oil saturation of 20-40%. The intervals are proving to be extremely large targets for commercial CO2 flooding and also have potential as large CO2 storage reservoirs.

ROZ work to date has concentrated on demonstrations of commercialization for CO2 EOR at isolated fields. Very little work has been done in an attempt to describe their origins and distribution. The starting point for this effort by the University of Texas of the PB and its research team will be development of several working hypotheses to describe both the evidence of their presence and the origins of their development. A modeling effort will be undertaken in an attempt to demonstrate the validity of the postulates to observed subsurface conditions. Enhancement for the capacity to exploit potential ROZs nationwide is the strategic goal of this effort.

At this submittal stage, the leading candidate for their origin has to do with 1) early geological entrapments that were subsequently flushed by later (Laramide and mid-Tertiary) uplift causing hydrologic changes and lateral reservoir flushing. Other candidates include the long held belief that ROZs are actually just transition zones formed primarily by capillary forces within the pore system and basin-wide tilt. Geographically speaking, plans call for starting a study of the north and east side of the Delaware Basin and west side of the Central Basin Platform. It is here that evidence of ROZs concentrate in several stratigraphic horizons. The San Andres, Grayburg, Glorieta and Clearfork intervals are proliferate with sample shows but actual established oil producing fields are rare. The effort will first gather the data in the region with a goal of focusing on one particular horizon. Well logs, groundwater samples and any core data that can be found will be gathered in an attempt to reconstruct what we might suspect would be the flow path that flushed the oil from the geological entrapment. The evidence to be gathered will include any that suggests entry and exit paths for and evidence of the flushing.

The zonal properties will be established, the flow channels approximated, and input and exit conditions bounded. With this flow path hypothesis developed, a regional hydrological model will be constructed. The model will examine charge and discharge points in an attempt to develop a consistency with the observed data points of sulfur deposits, water salinity observations, and tilted oil/water contacts in reservoirs within the flow path. Team member ARCADIS will provide the ground water expertise and model work.

The final report will be the first attempt to document the spectrum of data suggesting origins and distribution of the residual oil zones in the PB. Methodology for determining the presence and distribution of ROZs in other flow channels or “fairways” within the PB area and other regions of the country will be outlined. Parametric sensitivities of ROZ will be examined using the developed geohydrologic model. Methodology developed could be extended to other regions of the U.S. to assist with predicting occurrence and distribution of residual oil zones.

The data acquired and model developed will provide features of the ROZs that can be tested with new wells and cores. The results of this study could be extended to a demonstration project wherein the developed understanding can be tested through new wells and/or pilot flooding. The cost and data sharing industry partners are the likely hosts, Legado Resources (LR) and/or Chevron.

Most of the mature oilfields in the U.S. are now controlled by small producers. The impact for small producers should be to add dramatic increases in targets for enhanced recovery from mature oil and gas fields as well as reduced environmental impact and development costs.

Principal Investigators: Dr. R. C.Trentham, Mr. L. S. Melzer