12. Petroleum system processes that control petroleum generation, migration, trapping, and retention in continuous accumulations

The focus of this petroleum system modeling research is to evaluate processes important to oil and gas generation, migration, accumulation, and retention at reservoir to basin scales, and at one, two, three, and four dimensions. Petroleum system modeling is most readily applied to conventional reservoirs and basins, particularly in areas with structurally trapped petroleum. Continuous reservoirs, sometimes termed basin-center or unconventional, are an increasingly important source of gas resources within the United States. Modeling has not been as extensively or effectively applied to continuous resources. One reason for this is that types and characteristics of trapping mechanisms are more subtle than for conventional accumulations. Continuous accumulations involve anomalous pressure histories, presence of updip water, low reservoir permeability, and proximity to thermally mature petroleum source rocks. The purpose of this study is to design a model for continuous resources that can also be used as an analog.

Modeling integrates and analyzes many types of data essential in understanding the evolution of petroliferous areas, including (1) petroleum system assignments such as reservoir, seal, and source rock intervals; (2) vertical and lateral distribution and lithologic properties of strata; (3) timing and extent of depositional, hiatus, erosional, and tectonic events; (4) influence of open and (or) closed faults through time; (5) seal capacity of faults and lithologic layers, and associated (6) compaction history of lithologies, and (7) capillary pressure; (8) static or changing heat flow and other temperature variables; and (9) kerogen type and kinetics of source intervals. Models are calibrated to data such as measured thermal maturation, pressure, and temperature. Input variables can be risked using Monte Carlo, Latin Hypercube, and other methods. Background information and some of the capabilities and potential results of the modeling are in Higley and others (2006).

Petroleum system modeling allows integration of numerous geoscience variables to calculate their relative influences through time on oil and gas generation, migration, and trapping—complex processes that are generally researched as small subsets. It is important to model the relationships through time among formation pressure and temperature and associated changes in maturity of petroleum source rocks. In the establishment of continuous gas systems, it may well be that capillary pressure gradients supply the dominant force resisting hydrocarbon flow, buoyant and viscous forces are generally low or negligible, and the primary driving force is gas pressure. Changes in types of pressure, in temperature, and other variables through time are analyzed using the modeling software and are primarily controlled by the assignment of lithologic and other physical and geochemical properties of the strata. Progress in this area will require better understanding of 3-D fluid flow in low-permeability porous media.

Greater knowledge of the mechanisms of oil and gas generation and expulsion from source rocks and the mechanisms controlling fluid and gas movement, trapping, and retention are critical to understanding these resources and to increasing rates of discovery and production. Results of the modeling will yield benefits in the areas of petroleum exploration and development, USGS assessment methodology, and in understanding behavior of petroleum systems. This is particularly true for continuous accumulations, which are not well understood. These benefits would be especially timely as U.S. gas production levels are nearly static in the face of increasing domestic demand and projected reliance upon gas imports.

Expected results include a greater understanding of relative influences through time of lithologic variation, kerogen type and kinetics of source intervals, temperature and pressure histories, hydrodynamics, and depositional and erosional events on generation, migration, trapping, and retention of oil and gas in continuous accumulations. Several areas are currently compiled and available for modeling. These include the Wattenberg gas field of Colorado (Higley and others, 2003; Higley and Cox, 2005) and the Western Canada Sedimentary Basin of Alberta and Saskatchewan (Higley and others, 2005a, 2005b; Roberts and others, 2005; and Higley and others, 2006). The Anadarko Basin Province, including the Hugoton-Panhandle field, is a potential study area for this modeling because it is a mature basin that contains one of the largest gas fields in the United States and has a wealth of petroleum production data, and geologic and geochemical data and research that are currently being compiled for model construction.

The digital information needed for 1-D, 2-D, 3-D, and 4-D models includes (1) isopach and structure contour maps of reservoir, source, and seal intervals; (2) fault system maps; (3) well history and production data for all wells in the province; (4) vitrinite reflectance and other thermal maturation data; (5) borehole and DST temperatures; and (6) background research that incorporates time periods of deposition and erosion, tectonic events, heat flow, and pressure histories. Constructed 1-D models are used to calibrate 4-D petroleum system models. USGS personnel are expert in the use of PetroMod, EarthVision, and other mapping and modeling software, can provide training in the use of these programs, and assistance in how to integrate the diverse data for the petroleum system models. The USGS also possesses considerable expertise in the geology of low-permeability basins in the U.S., an outcome of decades of field study and mapping.

References

Higley, D. K., Cox, D.O., and Weimer, R.J., 2003, Petroleum system and production characteristics of the Muddy (J) Sandstone (Lower Cretaceous) Wattenberg continuous gas field, Denver Basin, Colorado: American Association of Petroleum Geologists Bulletin v. 87, no. 1, p. 15–37.

Higley, D.K., and Cox, D.O., 2005, Oil and Gas Exploration and Development along the Front Range in the Denver Basin of Colorado, Nebraska, and Wyoming, in Fishman, N.S., ed., Energy Resource Studies, Northern Front Range, Colorado: U.S. Geological Survey Professional Paper 1698, p. 9–53. http://pubs.usgs.gov/pp/2005/1698/

Higley, D.K., Henry, M.E., and Roberts, L.N.R., 2005a, Petroleum System Modeling of the Western Canada Sedimentary Basin—Isopach Grid Files: U.S. Geological Survey Open-File Report 2005–1421, 14 p. http://pubs.usgs.gov/of/2005/1421/

Higley, D.K., Henry, M.E., Roberts, L.N.R., and Steinshouer, D.W., 2005b, 1-D/3-D Geologic Model of the Western Canada Sedimentary Basin: RMAG, The Mountain Geologist, April 2005, v. 42, no. 2, p. 53–65.

Roberts, L.N.R., Higley, D.K., and Henry, M., 2005, Input Data Used to Generate One-dimensional Burial History Models, Central Alberta, Canada: U.S. Geological Survey Open-File Report 2005–1412, 14 p. http://pubs.usgs.gov/of/2005/1412/

Higley, D.K., Lewan, M., Roberts, L.N.R., and Henry, M.E., 2006, Petroleum System Modeling Capabilities for Use in Oil and Gas Resource Assessments: U.S. Geological Survey Open-File Report 2006–1024, 18 p. http://pubs.usgs.gov/of/2006/1024/

Proposed Duty Station: Denver, CO

Areas of Ph.D.: Geologic and (or) hydrologic modeling of fluid flow in sedimentary basins and (or) petroleum reservoir modeling and (or) computational fluid dynamics

Qualifications: Applicants must meet one of the following qualifications: Research Geologist, Research Geophysicist, Research Hydrologist

(This type of research is performed by those who have backgrounds for the occupations stated above. However, other titles may be applicable depending on the applicant's background, education, and research proposal. The final classification of the position will be made by the Human Resources specialist.)

Research Advisor(s): Debra Higley-Feldman, (303) 236-5791, higley@usgs.gov; Phil Nelson (303) 236 1322, pnelson@usgs.gov; Christopher J. Schenk, (303) 236-5796, schenk@usgs.gov; Michael D. Lewan, (303) 236-9391, mlewan@usgs.gov

Human Resources Office contact: Kathleen Scheich, (303) 236-9581, kscheich@usgs.gov

Summary of Opportunities