08123-19

Goal
The objective of this project is to describe and gather the data needed to determine the distribution of residual oil zones (ROZ) in a portion of the Permian Basin and to develop a methodology template for determining the presence and distribution of ROZs in other areas of the Permian Basin and elsewhere.

Data such as well logs, field specific oil-water contact data, groundwater samples and core data will be collected from specific horizons and a flow path (or fairway) that might have flushed oil from geological entrapment will be defined. Zonal properties will be established, flow channels approximated, and input and choke point (exit) conditions bounded. A regional hydrological model will be constructed of the hydrodynamic fairway that will 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. The final report will document the spectrum of data suggesting origins and distribution of the residual oil zones in the Permian Basin, and a methodology for determining the presence and distribution of ROZs in other fairways within the Permian Basin area and other regions of the country will be outlined.

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.

Performers
University of Texas of the Permian Basin
Cost and data sharing by Chevron Corporation, Yates Petroleum, and Legado Resources

Background
The Permian Basin of the U.S. is noted for having vertically extensive intervals (~200-300 feet thick) beneath the oil/water contacts of major reservoirs. Some of these residual oil zones (or ROZs) found in the largest of the fields producing from the San Andres Formation have been estimated to contain over a billion barrels of oil in place at an average oil saturation of 20 to 40%. These intervals are large targets for commercial CO₂ flooding or potential CO₂ storage.

ROZ characterization to date has concentrated on demonstrations of CO₂ EOR at isolated fields. Very little work has been done to define a model explaining the origin and distribution of ROZs.

At this point, the leading hypotheses for their origin are: 1) early geological entrapment with subsequent flushing caused by uplift, or 2) transition zones formed primarily by capillary forces within the pore system and basin-wide tilt. The north and east side of the Delaware Basin and west side of the Central Basin Platform provide evidence of ROZs in several stratigraphic horizons (the San Andres, Grayburg, Glorieta and Clearfork intervals).

Potential Impacts
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 fields.

Accomplishments
This project began in July 2009. Both the Project Management Plan and the Technology Status Assessment have been completed. The Project Management Plan consists of a work breakdown structure that concisely addresses the objectives and approach for each task with all major milestones and decision points. The Technology Status Assessment describes the state-of-the-art of the proposed technology.

Current Status (January 2011)
The key tasks to be undertaken are outlined below.

Experience Gathering (Full Permian Basin Area) – The overall nature and extent of the maximum oil entrapments in the carbonate rocks rimming the north rims of the Delaware and Midland Basins will be investigated. The same will be done for the west and east sides of the Central Basin Platform (CBP). Particular attention will also be place on the south side of the CBP as an exit path. The scope of the relict entrapment indicators will include residual oil presence and saturations, water salinities and acidity, sour nature of the oil and gas, and OWC tilts.

The research team will also investigate basin-wide sulfur deposits. This should prove to be a critical data set. Elemental sulfur deposits form where hydrocarbon-bearing fluids exit a water-drive system through fractured sulfur bearing (anhydrite, gypsum) strata. The moving fluids contact the sulfur bearing seals whereby the displaced hydrocarbons are consumed by sulfate reducing bacteria. The fact that continual hydrocarbon nourishment is present due to the flushed hydrocarbons and that the sulfates are extensive, leads to large sulfur deposits. In the Permian Basin, locations of the sulfur deposits are indicators of hydrodynamic flow paths and, more specifically, suggest fairways of water movement and exit pathways.

Data Gathering (Permian Basin, Western Side) – The research team will first gather data in the north and east side of the Delaware Basin and west side of the Central Basin Platform with a goal of focusing on one particular reservoir horizon. Subsurface data will be gathered in an attempt to reconstruct the flow path(s) that flushed the oil from the original geological entrapments. The evidence to be gathered will include any pertaining to ROZ presence or that suggests entry and exit paths for and evidence of the flushing.

Flow Channels or Fairway Selection – The zonal properties will be established, the flow channels or fairways approximated, and input and choke point (exit) conditions bounded. With this flow path hypothesis, a regional hydrological model will be constructed. The data gathered will support an examination of charge and discharge points in an attempt to develop a consistency with the observed data points within the flow path.

The final report will document the spectrum of data suggesting origins and distribution of the residual oil zones in the Permian Basin. Parametric sensitivities of ROZ input parameters will be examined using the hydrologic model. The data and model will provide features of the ROZs that can be tested with new wells and cores.

Project Start: July 8, 2009
Project End: July 7, 2011

DOE Contribution: $630,934
Performer Contribution: $331,000

Contact Information:
RPSEA – Martha Cather (martha@prrc.nmt.edu or 575-835-5685)
NETL – Chandra Nautiyal (chandra.nautiyal@netl.doe.gov or 918-699-2021)
University of Texas of the Permian Basin – Dr. R. C.Trentham (trentham_r@utpb.edu or 915-552-2432)