January, 2002
HGS Meetings

HGS Dinner Meeting

"New Resource from Old Fields: Revitalizing Recovery in Shelf-bound Pliocene and Miocene-age Reservoirs, Gulf of Mexico"

Note: To view the figures, please refer to the hard-copy Bulletin .

Abstract:

Gas resource ultimate recovery projections have varied greatly over the past 30 years. Recent estimates by the Gas Research Institute put recoverable domestic resources as high as 422 TCF, nearly 50% higher than estimates made by state and federal government organizations. High uncertainty in gas recoverable projections is in part due to the uncertainty of recovering resources in highly complex fluvial/deltaic/deep marine clastic reservoirs of the Gulf Coast. Heterogeneity exists on all levels. Varying complexity of depositional systems and varying drive mechanisms are the two primary factors that cause differences in the ultimate recovery from reservoirs.

The Secondary Gas Recovery (SGR) research program, carried out by the University of Texas at Austin, Bureau of Economic Geology and funded by the U.S. Department of Energy (DOE), was begun in 1988 in response to growing realization of the amount of gas resources being left unrecovered in U.S. reservoirs. It is the goal of this long-standing research initiative to seek to better resolve the stratigraphic and structural complexities and present methods to reduce uncertainty and improve gas production. The challenge is to identify a process design and enhanced technology for reducing uncertainty in between-well scale reservoir architecture characterization, to identify previously unrecognized stratigraphic and structural play types and to improve economic scenarios for field development. Outcomes must be user friendly, inexpensive to implement and non-manpower intensive. New play concepts must be of large enough scope to drive revitalization of existing fields. Prior to 1998, projects in SGR had been confined to onshore studies; however the most recent project marks the first in offshore federal waters.

Miocene strata account for approximately 40% of all hydrocarbons produced and 40% of all remaining proven reserves in the Gulf of Mexico. These units are mostly restricted to mature fields on the present continental shelf (< 200 m water depth). Two fields, Starfak and Tiger Shoal, located in the Central Planning Area of the northern Gulf of Mexico Shelf, Vermilion and South Marsh Island Blocks, are the current study area for the DOE Offshore SGR research initiative (Fig. 1). Integration of sequence stratigraphy, conventional interperative and attribute extraction geophysical methods, well-log analysis and seismic-to-petrophysics transform and three-dimensional reservoir flow simulation modeling have been used to identify bypassed resources and new nontraditional targets across the area. At certainty, estimates now suggest the possibility of at least 300 Bcf of additional resources available for exploitation within the study area.

Starfak and Tiger Shoal fields are located in offshore Louisiana immediately north of the Salt Deformation Province. Although the area’s large-scale structural folds are a product of deep salt movement, geologic conditions here are structurally simple as compared with the complex diapiric deformation that occurs to the south. The fields are associated with several subregional normal faults and associated antithetic faults that are responsible for additional structural partitioning within these two large fields (Fig. 2, pg. 17). Depositional environments across the study area range from subaerial incised valleys to deltaic to deep marine basin floor fans (Fig. 3, pg.17). The section is progradational, punctuated by higher-frequency flooding and transgressive events. Sediments prograded from north-to-south.

Several stratigraphic trap types, as well as secondary structural traps exist unexploited across the study area. Resources show systematic preferential distribution within seven play types. New seismic methods and attributes have been developed to improve seismic interpretation and inversion of data to petrophysical parameters for population of three-dimensional reservoir models. Seismic geomorphology and sedimentology provide a detailed look at the architecture of these complex reservoir/seal systems (Fig. 4, pg. 19). Several new targets have been tested by industry partners and proven successful. These results are being extrapolated into a more regional area utilizing previous play classification work by BEG and Mineral Management Survey researchers and will provide the roadmap by which resource growth and new opportunity can be exploited throughout the Gulf of Mexico.

For digital abstracts and extended abstracts visit www.beg.utexas.edu/resprog/sgr/index.htm

Biographical Sketch:

Dr. Lesli J. Wood. Email lesli.wood@beg.utexas.edu

HGS Environmental / Engineering Dinner Meeting

"Hydrogeology and Simulation of Ground-Water Flow and Land-Surface Subsidence in the Chicot and Evangeline Aquifers, Houston Area, Texas "

Abstract:

In November 1997, the U.S. Geological Survey, in cooperation with the City of Houston’s Utilities Planning Section and the City of Houston’s Department of Public Works & Engineering, began an investigation of the Chicot and Evangeline aquifers in the greater Houston area to better understand the hydrology, flow, and associated land-surface subsidence. As part of the investigation, a numerical model was developed to simulate ground-water flow and land-surface subsidence in the greater Houston area. The study area covers 18,100 square miles. Simulations were made under transient conditions for 31 ground-water withdrawal (stress) periods that began January 1, 1991, and ended on December 31, 1996. The finite-difference computer code MODFLOW was used to simulate the Chicot and Evangeline aquifer system. Simulation of land-surface subsidence and water released from storage in the clay layers was accomplished using the Interbed-Storage Package. The elastic and inelastic skeletal specific storage coefficients are parameters that were calibrated interactively with potentiometric surfaces of the aquifers. Simulated and measured potentiometric surfaces of the Chicot and Evangeline aquifers for 1977 show a good correlation. Water-level measurements indicate that by 1977, large volumes of ground-water withdrawal in east central and southeast areas of Harris County had caused the potentiometric surfaces to decline as much as 250 feet below sea level in the Chicot aquifer and as much as 350 feet below sea level in wells in the Evangeline aquifer. Simulated and measured potentiometric surfaces of the Chicot and Evangeline aquifers for 1996 also show a good correlation. The large potentiometric-surface declines in 1977 in the southeastern Houston area now show significant recovery. In 1996, new centers of potentiometric-surface declines are shown much farther to the northwest. Potentiometric surface declines of more than 200 feet and 350 feet below seal level in the Chicot and Evangeline aquifers, respectively, were measured in observation wells and simulated in the flow model.

Biographical Sketch:

Mr. Kasmarek received his BS in geological sciences from the University of Texas at Austin. He served in the Strategic Air Command maintaining navigation electronics in the late seventies and then became a logging consultant in San Angelo, Texas. He worked as a hydrogeologist for the USGS in Houston from 1984 to 1994 and then was promoted to the Chief of the Groundwater Section. In 1997, he created a groundwater flow model for the Chicot and Evangeline aquifers covering a 21 county area. Currently, he is working on a ground-water flow model (MODFLOW) of the Chicot, Evangeline, and Jasper aquifers that encompasses a 30-county area and incorporates the Interbed-Storage Package to compute land-surface subsidence interactively during transient model calibration.

HGS International Dinner Meeting

"Chronostratigraphic Isopach Mapping of Sequences of the Arabian Plate"

Vendors:

GETECH -a new ArcView project covering Arabia contact: Jeff Martin, Marketing Manager, GETECH, Inc., (281) 240-0684, jrm@getech.com
www.getech.com

C & C Reservoirs -delivers a Web-based Digital Analogs System with extensive data, re-interpretation and analyses on nearly a thousand of World's most important fields and reservoirs. For details, please contact us at (713) 776-3872 or e-mail us at info@ccreservoirs.com

GEOMARK - will show summaries of their studies of oils and source rocks from the Middle East and Lower Arabian Gulf. Contact: Steven M. Brown, 281 856 9333, biomarkers@aol.com

Abstract:

Figure: Figure 1.
Lower Cretaceous isopach of the Arabian Plate constrained by wells that spud below interval, wells the penetrate, wells with interval absent in subsurface, outcrop of subcrop, and wells that have thickness of lower Cretaceous present. See the map legend for symbols of each of these elements.

Having as a product objective, regional maps which enable:

  1. construction of cross-sections,
  2. understanding sequence distribution, and
  3. modeling of maturation;

we describe the construction process of plate-wide chronostratigraphic isopach maps from a large multi-country area. The Arabian plate database is comprised of over 46,000 top records for 1,400 aged stratigraphic units and 2,640 mappable wells with tops. Four tables are used, including well header, tops, stratigraphic age, and surface ages. The most important contribution of this mapping system is that it handles multiple stratigraphic nomenclatures, maps unconformity-bounded sequences, and takes full advantage of multiple constraints to enhance mapping and zero-edges. Once set up, the system also adapts other kinds of mapping. Figure 1 represents a mapped example of the lower Cretaceous of the Arabian Plate.

Absolute ages for lithostratigraphic units are inferred from the literature and superposition. For age quality control I have devised a spreadsheet-database cycle system that focuses on superposition/age problems. I re-run the cycle until superposition is obeyed and ages are constrained to literature. A dual query-system is used to obtain thickness values. The first part of the duel query-pair delimits upper and lower ages of the unit in question and searches downward in the database for each side of the age bracket. A second part of the query uses the same age delimited interval and then searches upward from the base and downward from the top for minimum and maximum depths. Querying out the largest thickness value from the dual query maximizes data control.

Series of linked queries enable constraint of mapping by using

After querying or assigning these individual elements they are aggregated into a combined table, a) through e), to constrain contouring. Then a) through e) are independently mapped superimposing them on the contour result with distinct identifiers, to enhance appearance for quality control. In addition to visual study of individual maps, stratigraphic thickness elevation plots are used to find and check data outliers.

Fifteen unique interval maps have been constructed in GIS, these include

  1. Neogene,
  2. Oligocene,
  3. Eocene and Paleocene,
  4. Upper Cretaceous,
  5. Middle Cretaceous,
  6. Lower Cretaceous,
  7. Upper and Middle Jurassic,
  8. Lias and Triassic, and
  9. each (9-15) Paleozoic System.
This method adapts to making lithostatigraphic, structural, subcrop, worm’s eye, and time-hiatus maps.

Biographical Sketch:

Walter H. Pierce is the director of WHPierce Exploration located in Cypress, Texas, USA His background includes consulting after early retirement subsequent to 17 years of experience with international groups within Amoco. He holds Ph.D. and MSc. degrees in Geology from the Colorado School of Mines and an A. B. from DePauw University. Previously he taught Geology for eight years at Ball State University, University of Georgia, and The Colorado School of Mines. He also worked for the USGS in the Petroleum Group and in the Heavy Metals group. His recent work has focused on a review of Middle East source rock for exploration, hydrocarbon system analysis of the Arabian plate, undiscovered reserve assessment, multi-basin assessment of Central Asia and the Middle East, and new ventures. Mr. Pierce may be contacted at:

WHPierce Exploration:
12931 Bowing Oaks Drive,
Cypress, Texas, 77429,
Telephone: 281 376 3414,
Web page , Email: walterhpierce@yahoo.com

HGS North American Exploration Dinner Meeting

"The Ellenburger of West texas and the Devonian Keg River of Western Canada:
Case Studies where Deep-Burial Dissolution Controls Dolostone Reservoir Development "

Abstract:

Case studies of Devonian dolostone reservoirs from Western Canada (Keg River, Swan Hills, Leduc, Blueridge, Wabamun) establish diagenetic/porosity relationships that bear on the timing of porosity evolution in Ellenburger dolostones from West Texas.

Deep-burial dissolution controls reservoir quality in many of these deeper Devonian reservoirs. Diffused plane-polarized light and fluorescence microscopy allow recognition of relict textures and diagenetic fabrics in these dolostones previously invisible with standard petrographic light. These enhanced petrographic techniques prove that replacive dolomites, and their subsequent dissolution, are deep burial in origin. Further, what often appears to be vuggy or intercrystalline porosity is, in fact, fabric-selective moldic porosity, demonstrating that reservoir quality in many of these dolostones is facies-controlled.

Detailed core studies of Keg River dolostone pools from the Rainbow Sub-Basin of Northwestern Alberta consistently revealed that dolomites replaced carbonate grains already sutured by pressure solution. Dolomitization, therefore, occurred coincident with, or after, incipient pressure solution. Since these grains were leached, their dissolution also occurred during burial. Deep-burial secondary porosity development was further evidenced by dissolution of dolomitized grains and matrix along stylolites, or along fractures that cut stylolites. Stylolites and fractures often terminated into secondary pores, implying that they were conduits for diagenetic fluids. Dissolution of late-forming saddle and other dolomite cements provided further evidence of burial dissolution. Brecciation, which was not uncommon in this sequence, was simply a grander expression of burial dissolution. Breccias formed under deep-burial conditions consisted of clasts containing stylolites that were rotated at different angles to each other and the horizon. Keg River diagenesis and porosity evolution, as well as pool entrapment, was controlled by reactivated basement faults related to a nearby master wrench fault, the Hay River Fault.

Ellenburger dolostone reservoirs on the Eastern Shelf of Texas, such as Suggs and Withers Fields, underwent deep-burial replacement dolomitization and subsequent dissolution. Petrographic criteria noted above for the Keg River in Canada are replicated in cores and thin sections of these West Texas dolostones. These timing relationships, along with other diagenetic fabrics, implied that faults and fractures related to a master wrench fault, the Ft. Chadbourne, were the conduits for diagenetic fluids that promoted deep-burial dissolution of dolomites and secondary porosity development. Unconformity-related diagenesis was not responsible for reservoir quality in these dolostones.

Case studies of dolostone reservoirs from Canada and the Ellenburger demonstrate that the timing of dolostone reservoir development is more accurately resolved when enhanced petrographic techniques are rigorously applied. Failure to understand the timing of secondary porosity development in any carbonate reservoir severely limits one’s ability to exploit it.

Biographical Sketch:

Jeff Dravis is a carbonate geologist and owner of Dravis Geological Services, which conducts exploration and reservoir development projects in the U.S., Canada and overseas. A number of these projects involved studies of structurally altered sequences, explaining Jeff’s interest in the influence of wrench faulting on carbonate diagenesis and porosity evolution. Jeff is also president of Dravis Interests, Inc., through which he conducts applied training seminars for industry. Since 1987, Jeff has taught nearly 100 in-house and field carbonate seminars.

Jeff received his B.S. (Geology) from St. Mary’s University in San Antonio, his M.S. (Marine Geology) from the University of Miami’s Rosenstiel School of Marine and Atmospheric Sciences, and Ph D (Geology) from Rice University, Houston. He has been an adjunct professor at Rice University and the University of Miami (Florida) since 1987.

HGS Lunch Meeting

"100 Years of Exploration and Production at Jennings Field"

Abstract:

The Jennings Field of Acadia Parish, was the first commercial oil discovery in Louisiana. The Jennings Field was discovered just 9 months after the Spindletop discovery in Texas, making it one of the earliest discoveries in the Gulf Coast. The field has produced over 118 MMBO and 51 BCFG from Miocene through Oligocene Anahuac and Frio age sands associated with the supercap and flanks of a shallow salt dome. The field is still producing today, with 1999 annual production of 141 MBO and 224 MMCFG. Initial production from supercap hydrocarbon accumulations yielded spectacular gushers and prolific flow rates estimated at 7000 barrels per day for the discovery well. Supercap production peaked in 1909 at 9 MMBO. Supercap production from the Jennings Field accounted for 67% of Louisiana’s cumulative oil production for the years 1901 to 1920. The Yount-Lee Oil Company established production on the flank of Jennings dome in 1928 after discovering hydrocarbon accumulations on the salt flank of Spindletop dome in 1926. Development of the flank acreage revived field production to a peak of 8 MMBO in 1939.

The Jennings dome has a slightly elliptical northwest-southeast orientation to the salt with the steepest salt face on the northwest flank. The salt exhibits an overhang on the east flank with associated hydrocarbon production. A shallow Miocene mineralized sand section is also associated with this eastern flank. The dome has not been adequately evaluated seismically. Limited seismic control includes a 1996 3D seismic survey over the southern half of the dome and a few older 2D seismic lines.

Biographical Sketch:

Jeff Spencer is Chief Geologist for Osprey Petroleum in Houston. Jeff received a BS in geology from the University of Cincinnati and a MS in earth sciences from the University of New Orleans. Prior to joining Osprey, he was employed by UNOCAL (1998-2000) and Amoco (1981-98). Except for one year working Angola, Jeff has spent his career as both an exploration and development geologist working the Gulf Coast onshore and Texas/Louisiana shelf. 15995 N. Barkers Landing, Ste.350, Houston, TX, 77079-2493, phone 281-582-3117, fax 281-582-3139, Email: jspencer@orientpetroleum.com