Tight Sandstones of the Williams Fork Formation, Mesaverde Group in Southern Piceance Basin, Colorado By : Yulini Arediningsih GLGY 699 – Unconventional Gas Reservoir Characterization and Evaluation University of Calgary April 4, 2011
Objectives To overview key features of tight sandstonereservoirs of the Williams Fork formation,Mesaverde Group in Southern Piceance Basinincluding : • Reservoir characteristics • Fluid distribution in the reservoir and its controls To outline detection techniques of the naturalfractures related to basement fault features
Piceance BasinAfter Koepsell et al., 2003 (EIA, 2010 http://www.eia.gov/oil_gas/rpd/tight_gas.pdf
Current Status of Piceance Basin Current Status of Piceance Basin Properties : Porosity : 8.2% (avg) Matrix Permeability : 250 nanodardy Natural fracture permeability : 36-600 microdarcy Water Saturation : 55% Total OGIP : 311 TCF (106 TCF is from Southern Piceance Basin i.e. Grand Valley, Parachute, Rulison and Mamm Creek fields) Itsproved reserves is ranked 5th in the top 50 US gas fields (2009) Produced from a deep basin centered gas accumulation, inparticular from thick discontinuous lenticular fluvial sandstones of theWilliams Fork Formation, Mesaverde Group. Intensive resource development has increased total daily gasproduction from < 200 MMCFD (2000) to > 1 BCFD EURs : 1 to 2 BCF/well about 60-120 BCF/section Reference : Kuuskraa and Prestridge (1996) Cumella and Scheevel (2005) EIA (2009)
Geology Structures Common fold structures, Closely associated with the occurrence of enhanced natural fracture network NW – SE trending Have significantly affected and contributed to natural fracture system in the reservoirTremain and Tyler, 1997
Stratigraphy Two Phase Zone Continuously gas saturated Interval (1700’-2400’) Gas source 850’ (Yurewicz, 2005)
Key Features of the Reservoirs GAS STORAGE : Continuously gas saturated tight sandstonesof the William Fork formation CONDUITS : Naturally occurring fractures Abundant natural fractures in sandstones of the Iles formation and upper part of the Williams Fork formation. The fractures largely control fluid migration within the formation. Characterized by lower spacing and lower vertical and lateral extent GAS SOURCE : Cameo Coal zone at >6000ft depth, achievedhigh thermal maturity PROCESSES AND CONDITIONS : Pervasive natural fracturing results from extensive over pressuring conditions in Cameo Coals due to huge volume gas A transition zone of mixed gas – water saturated sandstones above the continuously gas-saturated interval. Restricted low fluid mobility because of low permeability sandstones
Water and gas distribution within the William Fork formation in Piceance Basin (After Yurewicz, 2005)
Detection of the Natural FracturesMethods :Integration of geologic, geophysical, and numerical basin modeling that cancost effectively locate fractured areas where advanced seismic methodscan subsequently be applied. Hi-Res aeromagnetic data + 2-D seismic remote sensing imageryto delineate the geometry of the to provide consistency basement structure. to the interpretation Linked with a numerical basin model A prognostic fracture mapping model
Detection of the Natural Fractures A prognostic fracture mapping model Calibrated with local and regional integrated fracture data Selected sites for the 3-D multi-azimuth P-wave reflection surveyThe 3D seismic survey : To target subsurface fracture sets especially in southern part of the basin Target depth is 4000 to 7000 ft. To evaluate the P-wave azimuthal anisotropy (which affects AVO, velocity,frequencies) and to determine relative fracture density and orientation. Production and well tests will verify the presence of open fracture sets andthereby validate the integrated exploration approach.
Results and Conclusions Key reservoir features in the Piceance basin : thick, maturedCameo coals, naturally occurring fractures due to over pressured condition and gas-saturated reservoir with little movable water. The naturally occurring fractures control the mobility and distribution of the fluid within the reservoir Fractured production trends : NW-SE, parallel to the faults of overlying deep basement Numerous basement faults have been located indicating many undrilled fracture prone areas are present in the basin. A 3-D survey provides a powerful technology for identifying structural features that provide the essential fractured permeability pathways necessary for commercial production from low permeability reservoirs.
Selected ReferencesKuuskraa, V.A., and Prestridge, A.L. : Advanced Technologies for Producing Massively Stacked Lenticular Sands, SPE 35630. This paper wav prepared for presentation at the Gas Technology Conference held in Calgary, Alberta, Canada 28 April – 1 May 1996.Cumella, S. and Scheevel, J. : Geology and Mechanics of the Basin-Centered Gas Accumulation, Piceance Basin, Colorado, An extended abstract, adapted from AAPG Hedberg Conference, April 24-29, 2005, Vail, Colorado.EIA, 2009, Top 100 U.S. Oil & Gas Fields By 2009 Proved Reserves, US Energy InformationAdministration.Tremain, Carol M. and Tyler, R. 1997. Cleat, fracture, and stress patterns in the Piceance Basin, Colorado: Controls on coalbed methane producibility. Rocky Mountain Association of Geologists, Fractured Reservoirs: Characterizations and Modeling Guidebook.Yurewicz, D.A., 2005, Controls on gas and water distribution, Mesaverde basin center gas play, Piceance Basin, Colorado (extended abstract): Search and Discovery Article #90042 (2005)Cumella, S., and Ostby, D., 2003, Geology of the Basin-Centered Gas Accumulation, Piceance Basin, Colorado: Rocky Mountain Association of Geologists, Chapter 10, 171-193.
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