Discovery and Development of Jonah Field, Wyoming - A New TCF Gas Field in the Green River Basin
Abstract:
Jonah field is currently producing over 175 MMCFG/D from over-pressured fluvial channel
sandstones of the Upper Cretaceous Lance Formation. The field was discovered in 1975, but due to market
conditions and primitive stimulation methods, the field was not economic. In 1992, McMurry Oil bought
the field, which consisted of three wells, and invoked new drilling and completion technology that
unlocked the full potential of the play. Jonah field has now grown beyond 90 wells and is poised to
become the next TCF gas field in the Rocky Mountain region.
The main producing interval in Jonah field is the Lance Formation (Upper Cretaceous - Maastrichtian). The depositional setting of the Lance is known to be a large alluvial plain composed of heterolithic floodplain deposits and multiple channel complexes that flowed eastward from ancestral highlands to the west. Braided stream deposition was dominant and can be segregated into an initial low net-to-gross sandstone interval in the lower Lance, a high net-to-gross interval in the middle Lance and another low net-to-gross interval in the upper Lance. Sandstones were deposited in channels 5-20 feet deep and 150-4000 feet wide, although some amalgamated sandstone intervals (i.e., Jonah interval) can be up to 100 feet thick and over a mile wide. Changes in fluvial architecture and amalgamation of the sandstones are a function of changes in sediment supply and subsidence rate (accommodation). Isopach maps of gross sandstone within the Lance Formation depict anomalously thick trends adjacent to major faults and suggest paleostructural control on deposition. Near the top of the Lance, a shale is present that is coincident with the top of the gas-saturated section.
Porosity and permeability in the sandstones conforms to a depth function. Sandstones below 10,500 feet have less than 10% porosity and less than 40 microdarcies of permeability, whereas sandstones above 8500 feet have up to 13% porosity and up to 1 millidarcy of permeability. Individual wells have an average of 600 feet of gross sandstone (range 260-1040 feet) and 335 feet of net sandstone (range 190-570 feet). Shaley-sand log analysis indicates pay intervals average 7.5% porosity (range <6-13%) and 43% water saturation (range 37-71%).
Volumetric reserve analysis of the over-pressured Lance interval, using average pay thickness, porosity, and saturation, indicates over 100 BCF gas in place per section. Estimated reserves of 0.7 - 13.0 BCFG/well are based on decline curve analysis of completed pay.
Total organic carbon values for mudstones in the Lance Formation average 1.0% and are volumetrically significant over the 2500 to 3000 foot thick producing interval. Much richer source rocks are present in thick coals of the Rock Springs Formation below the Lance. Data from production streams on early wells in the field show higher yields in the lower Lance (15-80 BO/MMCF) and lower yields (5-15 BO/MMCF) in the upper Lance. Pressure gradients in the field range from 0.55 to 0.59 psi/ft. The over- pressured nature of the field is a result of continuous upward migration of hydrocarbons into available pore space, possibly via microfracture seepage.
Speaker Biography
John W. Robinson is the Exploration Manager for McMurry Oil Company.
He is responsible for providing geoscience expertise in McMurry's
ongoing exploitation program in Jonah field, Wyoming, and for developing
additional exploration opportunities in the Rocky Mountain region.
Prior to working for McMurry, he worked for AMOCO Production Company,
Forest Oil Corporation, and Snyder Oil Corporation. In addition,
he has taught at Colorado School of Mines and has worked as a volunteer
for the Branch of Petroleum Geology at the U.S. Geological Survey.
He received Bachelor of Science and Master of Science degrees in
Geology from San Diego State University and a Ph.D. in Geology from
Colorado School of Mines. His research interests are in the
sedimentology of fluvial strata, multidisciplinary reservoir studies,
and investigation of basin-centered pressure compartments.
The TNRCC Voluntary Cleanup Program
Abstract:
Business activity on commercial and industrial properties at times results in contamination of the shallow soil and groundwater. At the very least, the contamination results in impaired market value and often makes the property difficult to sell. In some instances, the contamination can present potential long-term health risks to workers. In other instances, the contamination results in the property lying dormant or underutilized due to the liability and stigma associated with contamination.
The TNRCC Voluntary Cleanup Program (VCP) provides several incentives to encourage the cleanup and revitalization of contaminated properties. These include: liability protection to future owners once cleanup has been accomplished, liability protection for contamination that has come from an offsite source, the use of clean-up principles based on potential health risks.
Mr. Carsten will discuss different aspects of the voluntary cleanup program and its value in facilitating transactions of property with contamination. In particular, he will discuss: how the program is utilized by the business and environmental consulting community, the role of the new innocent landowner program, common pitfalls for those participating in the program, a brief update on proposed changes to the risk based cleanup rules, and an overview of Brownfields initiatives for the new year.
BIOGRAPHIES
Mr. Carsten is a geologist and unit manager in the TNRCC’s Voluntary Cleanup
Program. He is responsible for a team of unit managers reviewing site
investigation and remediation documents, including application of the
Risk Reduction Rules, for facilities participating in the Voluntary Cleanup
and Innocent Operator Program. Prior to joining the Voluntary Cleanup
Program, Mr. Carsten was a project manager in the TNRCC Corrective Action
Program. Mr. Carsten has been with the Commission for six years and
previously worked six years in environmental consulting in Houston
implementing site investigation and remediation projects. Mr. Carsten
holds a B.S. degree in Geology from Texas A&M University.
Paleo-Depositional Processes and Geological Drilling Hazards on the Continental Slope of Nigeria Identified using 3-D Seismic Coherency
Abstract:
When applied in the evaluation of slope areas in offshore blocks of Nigeria, 3-D seismic
coherency techniques provide dramatic images of near water bottom and subsurface features
which are not readily apparent on conventional seismic amplitude slices. Some of these
features are indicative of paleo-depositional processes, while others imply potential
geological drilling hazards.
IDENTIFICATION OF PALEO-DEPOSITIONAL PROCESSES
A 3-D seismic coherency horizon slice 144 ms below the water bottom shows numerous
depositional features, which, when viewed together, provide an interpretable picture of
the paleo-depositional processes. Interpretation of the depositional setting is
accomplished much more quickly than would be possible using traditional methods.
Linear features observed on the 144 ms coherency slice, which are up to 12 km in length and 100-200 m in width, are morphologically analogous to smaller scale (less than 1 km in length and 125 m in width) glide tracks formed by the down slope movement of outrunner blocks during a recent debris flow in the Kitimat fjord of British Columbia, Canada. Alow-coherency-bounded area with dimensions of 100 m x 250 m at the down-dip end of a glide track on the coherency slice is interpreted to be an outrunner block Vertical seismic sections and dip/azimuth displays show that the glide tracks and outrunner blocks exhibit topographic relief.
The coherency slice, associated dip/azimuth displays, and vertical seismic sections also suggest the presence of pressure ridges on the Nigerian continental slope. These pressure ridges occur both within a proposed debris flow and in front of a selected outrunner block. Pressure ridges have been identified at similar locations in the Kitimat debris flow.
The presence of glide tracks, outrunner blocks, and pressure ridges on the Nigerian continental slope indicate that debris flows have been the predominant depositional processes active on this continental slope during the Holocene.
DELINEATION OF GEOLOGICAL DRILLING HAZARDS
3-D seismic coherency can be used to delineate potential geological drilling hazards prior
to the acquisition of high-resolution hazard surveys. Potential geological hazards
identified on the Nigerian continental slope include shale ridges and diapirs, pockmarks,
and slumps.
Massive (3-5 km x 30+ km) low coherence subsurface shale ridges are orientated orthogonally to the present shelf edge. Random high coherency zones within the ridges indicate that the ridges are texturally heterogeneous. Some high coherency zones still retain a stratigraphic signature and are interpreted as blocks of the adjacent substrate that have been incorporated into the ridges. Shale diapirs, associated with the ridges, are observed in various stages of development, ranging from doming to collapse. Oil seeps, as evidenced by drop cores, are associated with some of the diapirs.
Shallow coherency slices show numerous circular to oblong pockmark-like features, 100 to 200m in diameter. These features are depressions, with depths up to 45 ms on vertical seismic sections, and occur in both random and non-random patterns. The non-random pockmarks line up along underlying features, such as faults and subsurface channel margins. The origin of these features is thought to be associated with the escape of pressurized gas/fluid through the seabed.
A coherency slice from 100 ms below the water bottom shows a rotational slump approximately 5 km wide by 17 km long. The head of the slump is characterized by extensional faulting and relatively large rotational blocks. Downslope, the slump sediments are chaotic and exhibit compressional structures. Recognizing slumps in the shallow subsurface indicates that an area has a history of instability.
Oil seeps associated with shale diapirs, pressurized gas/fluid associated with pockmarks, and historical instabilities are hazards which should be considered in development plans for the Nigerian slope.
BIOGRAPHIES
Susan Nissen is a Research Scientist with Amoco’s Exploration and Production Technology
Group in Tulsa. She received a BS (1983) in geophysics from the University of Delaware
and a Ph.D. (1992) in marine geophysics from Columbia University. Since joining Amoco in
1991, Susan has worked in the areas of high-resolution seismic data analysis,
stratigraphic modeling, and seismic attribute analysis. She is currently Agreement
Coordinator for the Enhanced Multi-Attribute Seismic Analysis Team, which is
responsible for the development and geological calibration of seismic attributes
such as coherency and spectral decomposition. She is a member of AAPG, AGU, GSA, SEG, GST,
and TGS.
Norman Haskell is a Research Associate at Amoco’s Exploration and Production Technology Group in Tulsa. During the last four years, he has worked with a technically diverse team, which has been responsible for developing, implementing, and calibrating seismic attributes such as coherency and spectral decomposition. His work has principally focused on geological calibration of seismic attributes. Norm worked for Texaco in the Permian Basin from 1966-1970 and Sun Research/Exploration in Dallas from 1975-1979. In 1979, he joined Amoco’s Tulsa Research Center where he provided sedimentological support to both Amoco’s International and Domestic Groups. He received a BS degree in geology from Augustana, 1964; an MS degree in geology from Iowa State University, 1966; and a Ph.D. in marine geology/sedimentology from the University of Connecticut in 1975. He is a member of the SEPM, IAS and AAPG.