DE-FC26-05NT42660

Goal:
The goal of this project is to provide petrophysical formation evaluation tools related to relative permeability, capillary pressure, electrical properties, and algorithm tools for wireline log analysis of Mesaverde Group tight gas sandstones in Rocky Mountain basins.

Performer
University of Kansas Center for Research, Lawrence, KS

Results
Over 1,200 core plugs from unique depths and 985 paired core plugs have been obtained from full-diameter core from Mesaverde Group intervals in 37 wells distributed across seven Rocky Mountain basins (Washakie, Uinta, Piceance, Upper Greater Green River, Wind River, Powder River, and Sand Wash). Cores have been contributed to the project by five major gas-producing companies in the region and have been obtained from the U.S. Geological Survey Core Repository in Lakewood, CO. The wells in each basin were selected to provide a wide geographic distribution as well as adequate wireline log suites and core. The sampling program has been designed to obtain cores from all major lithofacies in each basin and also represent the range in porosity, permeability, and depth exhibited by the Mesaverde in these basins.

Benefits
Tight gas sandstones represent 72 percent (342 trillion cubic feet, or Tcf) of the projected unconventional resource (474 Tcf) for the United States. Rocky Mountain tight gas sandstones represent 70 percent of the total tight gas sand resource base, and Mesaverde Group sandstones are a principal productive unit in Rocky Mountain basins. Industry and government assessments of the regional gas resource, projections of future gas supply, and successful exploration and development operations depend on an accurate understanding of the tight gas sandstone reservoir properties and accurate tools for formation evaluation of drilled wells. The improvement in formation evaluation accuracy that will result from this project will help to more accurately quantify limits on gas producibility, leading to more cost effective development of tight gas sand resources. An active and aggressive web-based, publication, and short-course technology transfer program will make the results of this research available to the widest possible audience of potential users, maximizing its impact.

Background
Understanding the minimum gas saturation necessary for gas flow is fundamental to defining the tight gas sandstone resource. The objective of this study is to investigate the relationships among critical gas saturation, capillary pressure, electrical and basic porosity, permeability, and lithologic properties in the tight gas sandstones of the Mesaverde Group. Of key importance is the impact of these variations on natural gas drainage. A detailed and accurate moveable gas-in-place resource assessment is most critical in marginal gas plays, and there is a need for quantitative tools that can accurately define the limits on gas producibility.

This project will collect published advanced rock property data and at least 300 rock samples and digital wireline logs from four or five wells in each of the five major Rocky Mountain tight gas sandstone basins (Washakie, Uinta, Piceance, Upper Greater Green River, and Wind River). Basic properties will be measured on these core samples, and based on these properties, samples will be selected that represent the range of porosity, permeability, and lithofacies in the wells and basins. Additional measurements on the selected samples will include critical gas saturation; routine and in-situ mercury intrusion capillary pressure analysis; cementation and saturation exponents and cation exchange capacity; core description such as thin-section microscopy, including diagenetic and point-count analysis; and standard wireline log analysis. The compiled published data and data measured in the study will be input to a relational database. Web-based access to the data will be provided to allow the construction of rock catalog-format output sheets based on user-input search criteria. In addition, core and wireline log-calculated properties will be compared and algorithms developed for improved calculation of reservoir properties from log response. The scale dependence of critical gas saturation will be evaluated through bedform-scale reservoir simulations that parametrically analyze how critical gas saturation and relative permeability scale with size and bedding architecture.

Summary
The relationship between core and log petrophysical properties and lithofacies sedimentary characteristics is examined in Mesaverde Group tight gas sandstones from forty cores in the Washakie, Uinta, Piceance, Upper Greater Green River, Wind River, Sand Wash, and Powder River basins. Fine-grained intervals of the Mesaverde Group are dominated by mudstones and silty shales; burrowed, lenticular and wavy-bedded very shaly sandstones; and wavy-bedded to ripple cross-laminated shaly sandstones. Sandstone intervals are dominated by ripple cross-laminated and cross-bedded, very fine to fine-grained sandstones, low-angle cross-laminated to planar laminated sandstones, and massive sandstones. For all lithofacies undifferentiated in the cores sampled, grain density averages 2.654U+U0.033 g/cc (error of 1 std dev) with grain density distributions differing slightly among basins. Core porosity ranges from 0-25%, averaging 7.2% (n=2200). In situ Klinkenberg permeability ranges from 0.0000001-200 millidarcies, averaging 0.002 millidarcies. Characteristic of most sandstones, permeability at any given porosity increases with increasing grain size and increasing sorting though this relationship is further influenced by sedimentary structure and the nature of cementation. Multivariate and neural network permeability prediction methods exhibit a standard error of 4.5X and 3.3X respectively. Capillary threshold entry pressure and pore characteristic length are well correlated with permeability. Archie cementation exponent, m, can be modeled with a dual porosity matrix-fracture model with m approaching one as porosity approaches zero. Critical gas saturation is generally less than 5% but increases with increasing bedform complexity. Integration of wireline log analysis and core petrophysical relationships provides guidelines and equations for predicting reservoir properties.

The Mesaverde Project website has been set up at(http://www.kgs.ku.edu/mesaverde [external site]).

Current Status (January 2009)
All work is complete and is being compiled for web and final report presentation. One technical presentation was given at the American Association of Petroleum Geologists meeting in San Antonio, TX, April 20-23, 2008. Three technical presentations were given at the American Association of Petroleum Geologists (AAPG) Rocky Mountain Section/Colorado Oil & Gas Association Regional Meeting in Denver, CO, July 7-10, 2008. A workshop is being planned for the AAPG annual meeting in Denver, CO 2009. The final technical report and web presentation are being prepared.

Start Date: September 28, 2005
End Date: June 30, 2008

Anticipated DOE Cost: $411,030
Performer Cost: $102,804 (20 percent of total)

Contact Information:
NETL – Virgiina Weyland (Virgiina.Weyland@netl.doe.gov or 918-699-2041)
University of Kansas Center for Research – Alan Byrnes (abyrnes@kgs.ku.edu or 785-864-2177)

Publications
Byrnes, A.P., (2007, in press), “Issues with gas and water relative permeability in low-permeability sandstones,” in S. Cummella, K. Shanley, W. Camp (eds.), Proceedings of the American Association of Petroleum Geologists Hedberg Conference on Understanding, Exploring, and Developing Tight Gas Sands, Vail, CO, April 24-28, 2005, 30 pgs.

Crossplot of Klinkenberg proportionality constant, b, versus in-situ Klinkenberg permeability measured at 4,000 psi net effective stress using nitrogen gas. Reduced major axis analysis indicates the correlation can be expressed as b(atm) = 0.851 kik-0.341, n = 1264.

In-situ Klinkenberg permeability versus calculated in-situ porosity by basin. Range of porosity and permeability of Mesaverde sandstones is generally exhibited by all basins.