Top Seal Character and Sequence Stratigraphy of Selected Marine Shales in Gulf-Coast Style Basins
Date: Monday, April 10, 2000
Place: Westchase Hilton, 9999 Westheimer
Time: 5:30 pm Social 6:30 pm Dinner
Marine shales are top seals for approximately seventy percent of documented hydrocarbon accumulations, but represent one of the least studied elements of petroleum systems. Sealing capacity is determined from laboratory measurements (high-pressure mercury injection capillary pressure), which are used to calculate hydrocarbon column heights. The largest interconnected pore throats control seal capacity.
Pore throat size is influenced by numerous compositional (mineralogy, total percentage of clay, and organic enrichment) and textural (fissility, silt content, and degree of compaction) aspects of shales. Mineralogic analyses indicate an average composition of: 65% clay; 19% quartz; 4% feldspars; 5% pyrite; and 7% accessory constituents (authigenic carbonates, glauconite, bioclasts, and carbonaceous debris).
The TOC of these shales ranges from 0.79 to 4.00 (wt %). In general, seal capacity increases with increasing clay and organic content and decreases with increasing detrital silt content. The analyzed Tertiary shales (140 samples) record middle neritic to outer neritic/bathyal paleoenvironments of deposition. Mercury injection capillary pressure (MICP) data indicate that maximum top seal capacity ranges from 735 ft to 2,305 ft (oil column) with hydrocarbon saturations in the seal of 10 percent.
Calculated seal capacity typically exceeds hydrocarbon column heights by a factor of 5 to 20 times. Consequently, top seal capacity is not a significant risk in structures having four-way closure. The interpretation of seal analysis data within a sequence stratigraphic context reveals a systematic trend in top seal capacity. Shales occurring in the uppermost transgressive systems tracts and maximum horizons are excellent top seals. Shale samples from the lower part of transgressive systems tracts are good to excellent seals, whereas shales within highstand systems tracts have moderate to good sealing capacity. Some condensed intervals contain exceptional top seals.
Biographical Sketch:
William C. Dawson is a senior research associate with Texaco Upstream Technology in Houston, Texas, where he has worked since 1984. Previously he was employed by Eason Oil Company and HJH, Inc. His specialty areas are seal and reservoir sedimentology and diagenesis, and their use in basin analysis. He has extensive experience in rift basin studies with emphasis on international exploration. Dawson is a former associate editor of AAPG Bulletin and currently a participant in AAPG Visiting Geologists Program.
William R. Almon is a senior research consultant and Texaco Fellow at Texaco Upstream Technology in Houston. Previously he was employed by Cities Service Oil Company, Anadarko Petroleum, and as independent consultant. He has extensive experience in seal and reservoir characterization and the application of siliciclastic diagenesis to reservoir management. Almon has been a distinguished lecturer for both the AAPG and the Petroleum Exploration Society of Australia. Currently he is a participant and the vice-chairman for the AAPG Visiting Geologists Program.
"Hazardous waste disposal operations "
Date: Wednesday, April 12, 2000
Place: Jalapenos - 2702 Kirby (at Westheimer)
Time: Dinner 6:30 pm, Presentation 7:30 pm
The industrial sector of America is required to comply with some extremely stringent regulations as part of the privilege of doing business in this country. The talk will focus on the basic environmental regulations confronting industry and present an overview of the environmental regulations governing the petrochemical industry. Special emphasis is given to waste regulations in the oil and gas industry along with insights on dealing with some of the Railroad Commission and TNRCC guidelines and how they effect pipe lines.
Industry is confronted with managing numerous issues having potential impact on various media: air, water and soil. The talk offers industry's perspective on numerous environmental regulations, including the Clean Air Act, SARA, CERCLA, NPDES and RCRA. . Regulations govern the way industrial facilities control storm-water runoff, the amount and type of air emissions, and disposition of waste. Solid and hazardous waste regulations will be emphasized.
In Texas, the petrochemical industry has two different regulatory agencies with which to contend. Oil and gas exploration and transport through pipe lines are regulated by the Railroad Commission. Petrochemical refineries and other industries are regulated through the Texas Natural Resource Conservation Commission (TNRCC). The primary regulatory agency with jurisdiction over the routine waste and remedial action of a pipe line is determined by the service of that pipe line. Specific cases where both regulatory agencies have been involved will be covered.
Biographical Sketch:
Lyn Sadler has worked for more than 15 years in the regulatory and industrial sectors as an environmental specialist. Currently, he is an environmental specialist with Chevron Pipe Line Company, managing environmental regulatory issues with emphasis on waste management. He has extensive experience developing and implementing environmentally related practices and policies and has developed numerous procedural documents to assure compliance with state and federal regulations.
Prior to working for Chevron, Mr. Sadler worked for the Texas Water Commission, now an entity of the Texas Natural Resource Conservation Commission. He has a BS in biology and a BA in chemistry from the College of the Ozarks and an MS in biology from Lamar University.
Turbidites of the Lower Atoka Formation, Jacksonville, Arkansas
Date: Monday, April 24, 2000
Place: Westchase Hilton, 9999 Westheimer
Time: 5:30 pm Social 6:30 pm Dinner
This presentation will concentrate on deepwater fans of the Lower Atoka Formation, located within the frontal Ouachita Mountains of north-central Arkansas. The continued exploration of hydrocarbon provinces within collisional systems proves to be a reliable source for ongoing research in specific areas around the world. The Jackfork Formation, which is stratigraphically older than the Atoka Formation, has been interpreted and reinterpreted on numerous occasions as to its exact placement with a submarine fan complex for many years. Since the Atoka has rarely been studied in detail, it was felt that this would present the authors with the perfect opportunity to explore the complexities of another section within the Arkoma Basin.
The collision between Laurasia and Gondwana in the North American hemisphere resulted in a transition from a continental passive margin to a convergent margin. As the ocean basin was being subducted, the advancing northward thrust complex resulted in flexural deformation, creating the Arkoma Basin. Sediments that make up the Lower Atoka Formation, fill a portion of the Paleozoic foreland basin (Arkoma Basin) that extends from east-central Arkansas to south-eastern Oklahoma. The basin can be divided vertically into two sequences: (1) thin, shallow-marine, shelf deposits of Cambrian to lower Pennsylvanian age and, (2) a thick clastic overlying wedge of flysch to molasses type sediments (turbidites) of Pennsylvanian age. The sediments reach their greatest thickness of 6.5 km in the southern end of the basin where they were deposited longitudinally to prograding submarine fans in a relatively shallow to basinal setting.
Three separate facie have been described from the Lower Atoka Formation outcrop, located along US Highway 5, just north-west of Jacksonville, Arkansas. Facies I is comprised of stacked, amalgamated, thick-to-very-thick-bedded, massive sandstones; Facies II consists of intercalated sandstone and shale layers with varying bed thickness; and Facies III consists of massive shale beds which are morphologically different from one another. These shale beds occasionally contain layers of thin-bedded silty sandstones that represent slumps or debris flow deposits. Stacking patterns within the sequences are variable with upward-thickening, upward-thinning, and mixed sequences present. The sandstone sequences represent lowstand and transgressive time deposits in a channelised mid-fan to sheet sands (lobe) in an outer fan setting. The alternating sandstone and shales represent channel levee or overbank deposits that reflect both proximal and distal depositional settings. The thick shales represent either highstand system tracts, lateral overbank deposition due to avulsion of the centers of major sand deposition, or top fill of a channel forming during lowstand.
Biographical Sketch:
Christian Clark currently works for Reservoirs Inc./Core Laboratories as a reservoir geologist in the Petroleum Services Division studying deepwater cores from the Gulf of Mexico, central Asia and western Africa. He has worked previously with Dr. John Wrenn and CENEX, from Louisiana State University, describing cores from fluvial and lacustrine environments along the U.S. Gulf Coast Region by using palynological and micro-fossil identification techniques. Throughout this study, several hundred cores were described in detail and stratigraphic columns were produced from both palynology and x-ray radiograph techniques. Specific fossil horizons were mapped from the data collected and enabled the USGS to produce a detailed paleo-environment map of the Gulf Coast.
Christian has worked extensively with Dr. Arnold Bouma, from Louisiana State University, over the past couple of years in describing and interpreting deep basin formations. Previous and currently ongoing academic research with Arnold concentrates on interpreting the Lower Atoka Formation and how its sedimentary deposits are situated within a deepwater submarine fan complex. Christian and Arnold presented this work last year at the GCAGS Conference in Lafayette, Louisiana. This is the first paper in a series of four to be published over the next two years. The second paper on the Atoka Formation is near completion and will be presented at the GCAGS 2000 Conference in Houston, Texas.
Christian received his B.A. from Nicholls State University in 1993, went to the University of New Orleans for his MBA from 1994-1996 and received his B.Sc. from Louisiana State University in 1998.
Production characteristics of sheet and channelized turbidite reservoirs, Garden Banks 191, Gulf of Mexico, U.S.A.
Date: Monday, April 26, 2000
Place: Hyatt Regency Downtown 1200 Louisiana
Time: 11:15 am social, 11:45 am lunch
Garden Banks 191 is 160 miles from Lafayette, Louisiana in 700 feet of water. Since 1993, block 191 has produced over 210 BCF of dry gas from Pleistocene reservoirs. This paper will address the production characteristics of turbidite sheet (4500' sand) and channel (8500' sand) sand reservoirs. Understanding the distribution of shale breaks within both reservoir types is critical because the shales compartmentalize gas production and control water encroachment.
The 4500' sand interval is 1000 ft (305 m) of interbedded sandstones and shales typical of amalgamated and layered sheet sands (Mahaffie, 1994). The turbidite sands shale out rapidly to the south onto a salt-cored high that had topographic relief at the time of deposition. Three facies have been identified in cores and borehole images: thick-bedded sands, thin-bedded sands, and laminated shales. Electric log evaluations typically underestimate the effective porosity and overestimate the water saturation in the thin-bedded facies, leading to an underestimation of reserves.
Individual turbidite sand beds are 0.2 to 8.5 ft (6 cm to 2.6 m) thick, with most being less than 2 ft (0.6 m). Thin-bedded sheets are interrupted by a few, relatively clean channel and lobe deposits, which occur randomly through the 4500' sand interval. These relatively minor channel sands are 10 to 60 ft (3-18 m) thick. A core from the interval in the adjacent Block 236 structure shows that the fine- to very fine-grained sands are massive or planar- to ripple-laminated, suggesting deposition mainly from low-concentration turbidity currents. The sand is subdivided into four producing members separated by thicker intervals of the laminated shale facies that extend across the reservoir but pinch-out downdip into the aquifer. The reservoir has a strong water drive and is connected to a fairly extensive aquifer. Water encroachment occurs individually in each member and is constrained by the shale breaks. Horizontal permeability is greater than vertical permeability in the reservoir interval. For example, in a dual completion (A-6 well), member 3 watered out before the underlying member 4.
The 8500' sand is an approximately 900 ft thick, fining-upward channel deposited in a slope mini-basin formed by salt withdrawal. Cores and borehole images show the lower part of the channel fill to be dominated by thick (3.0-12.0 ft,) massive, fine- to medium-grained sands. Concentrations of rip-up clasts up to several feet thick are common both along the erosional bases of individual flow events and suspended within the deposits. These facies were probably deposited by high-concentration, sandy turbidity currents and other high-concentration sediment gravity flows (Lowe, 1982; Stelting et al., 1998.) Lower-energy facies, such as laminated sandstone and/or siltstone,interlaminated siltstone and shale, and homogeneous to laminated shale are scattered throughout the interval. These finer-grain deposits were deposited by thin-bedded and muddy turbidites.
Electric log evaluations of thick sands with abundant shale rip-up clasts underestimated the reservoir quality of the facies. Having continuous core was critical to estimating reserves, selecting intervals to perforate, and designing a development strategy for the channel sand reservoir.
Sand character, initial pressure data, and production history show the 8500' sand to have good vertical connectivity but poorer lateral connectivity. The unit is divided informally into five members based on shale breaks and perched water contacts. Initial RFT pressures indicate the stacked channels of members 3, 4, and 5 are connected vertically within the reservoir body. Members 1 and 2 form an abandonment phase that is not connected to the lower members. Perched water contacts and the pattern of water influx indicate lateral barriers in member 3 and between the A1 and A7 wells in members 4 and 5. Bottom hole pressures taken over several years show members 4 and 5 are acting as a single tank. Although initial pressures indicated member 3 was connected to members 4 and 5, the shale break separating members 3 and 4 appears to have acted as a barrier during production.
The aquifer downdip to the 8500' sand is either small or poorly connected to the reservoir as the sand has produced by a combination pressure depletion/limited water drive mechanism. Recoveries have been excellent, but the recovery efficiencies for oil would also have been much lower with the limited water-drive exhibited by the 8500' reservoir.
Acknowledgements
We thank Chevron and Spirit Energy for permission to publish this paper. We would also like to thank Mark Zastrow for his helpful comments and insight into the regional geology and Scott Turner for his help with the RFT data.
References
Clark, J. D., and K. T. Pickering, 1996, Submarine channel processes and architecture: Vallis Press (London), 231 p.
Cook, T. W., A. H. Bouma, and M. A. Chapin, 1994, Facies architecture and reservoir characterization of a submarine fan channel complex, Jackfork Formation, Arkansas, in Weimer, P., Bouma, A. H., and Perkins, B. F. eds., Submarine fans and turbidite systems: sequence stratigraphy, reservoir architecture, and production characteristics: GCSSEPM 15th annual research conf. (Houston), p.69-81.
Lowe, D. R., 1982, Sediment gravity flows: II. Depositional models with special reference to the deposits of high-density turbidity currents: J. Sed. Petrol., v. 52, p. 279-297.
Mahaffie, M. J., 1994, Reservoir classification for turbidite intervals at the Mars discovery, Mississippi Canyon 807, Gulf of Mexico, in Weimer, P., Bouma, A. H., and Perkins, B. F. eds., Submarine fans and turbidite systems: sequence stratigraphy, reservoir architecture, and production characteristics: GCSSEPM 15th annual research conf. (Houston), p. 233-244.
Stelting, C. E., W. J. Schweller, J.E Florstedt, D. S. Fugitt, G. J. Herricks, and M. R. Wise, Production characteristics of sheet and channelized turbidite reservoirs, Garden Banks 236 Field, Gulf of Mexico: EAGE/AAPG Third Research Symposium (Almeria, Spain), paper #A006.
Fugitt, D. S., C. E. Stelting, W. J. Schweller, J.E. Florstedt, G. J. Herricks, and M. R. Wise, 1999, Production characteristics of sheet and channelized turbidite reservoirs, Garden Banks 191, Gulf of Mexico, U.S.A.: Gulf Coast Association of Geological Societies, Transactions, v. 49, p. 254-265.
Biographical Sketch:
David Fugitt is a staff geologist with Chevron in Lafayette, Louisiana. He joined Chevron in New Orleans in 1978 where he worked both exploration and geophysical assignments in the Gulf Coast. In 1985, he moved to Lafayette where he has worked in field development and in the building of integrated subsurface and reservoir models. David received a BS in geology from the Ohio State University in 1976, and an MS from Texas A&M University in 1978. He is a member of AAPG, Lafayette Geological Society, New Orleans Geological Society, and SPWLA.
Charles Stelting has been a regional and reservoir stratigrapher/sedimentologist specializing in deepwater depositional systems in various Chevron companies since 1982. He currently works in the New Orleans office. Charles provides stratigraphic assistance in Chevron's operations in North America and overseas. He teaches several corporate courses emphasizing the stratigraphic and reservoir character of deepwater, deltaic, and fluvial reservoirs. Prior to joining Gulf and Chevron, he worked 7 years with the USGS Office of Marine Geology. Charles participated on the Deep-Sea Drilling Project (DSDP) Leg 96 on the Mississippi Fan in 1983. He received his BS in geology from Texas A&M University--Kingsville in 1980 and his MS from University of California - Riverside in 1989.
William Schweller has worked in petroleum research with Gulf and Chevron since 1982. His principal interests are in turbidite reservoirs and sequence stratigraphy of deepwater systems.
Gary Herricks has worked primarily in reservoir engineering during his 20 years in industry. He received his BS in petroleum engineering from Texas Tech University in 1979. Gary started with Tenneco Oil Company in the Rocky Mountain region where he was involved in several secondary and tertiary recovery projects. His last 15 years have been spent working reservoir engineering issues in the Gulf of Mexico. Since 1989, Gary has worked at Chevron in various capacities, including senior reservoir engineer, Garden Banks 191 project communication coordinator, petroleum engineering information technology coordinator, and most recently as reservoir engineering advisor.
Michael R. Wise is a senior petroleum engineer with Chevron U.S.A. Inc. and is currently working in the Gulf of Mexico business unit of the North American E&P Company. Wise has almost 22 years of combined experience with Gulf and Chevron and has worked in both the Gulf of Mexico and the Permian basin, primarily in production and reservoir engineering.
Rice University invites the Houston geoscience community to a symposium in honor of Albert W. Bally, Professor Emeritus.
The Albert W. Bally Symposium will bring together an international group of world-renowned geoscientists to honor Bert's great insight in combining geology and reflection seismology, which has been a hallmark of all his research and teaching.
Technical presentations that focus on regions of the world where Bert has conducted research for almost five decades such as the Appenines, Canadian Cordillera, and Gulf of Mexico will be presented by:
Simultaneously, "Bert Fest" presents the opportunity for participants to celebrate Bert's life-long achievements and dedication to the advancement of Geology and Geophysics. Bert Fest will consist of three events: a late afternoon reception and an evening banquet on Thursday, April 13, and and evening festival to conclude the symposium on Friday, April 14.