October, 2001
HGS Meetings

HGS GeneralDinner Meeting

"Workstation Visualization Techniques and Workflows: Examples from the Deepwater Gulf of Mexico"

Figure One

Abstract:

All phases of the upstream petroleum industry, from wildcat exploration to field development, now benefit from massive amounts of available data. Seismic interpretation in particular benefits from 3D seismic data volumes that nearly blanket the entire offshore Gulf of Mexico. Depth migration of seismic data has advanced to the point where the interpreter can literally treat views extracted from a three-dimensional seismic volume as a “digital outcrop”.

Armed with these data and well control for calibration, it is now possible to rapidly quantify stratigraphic mapping, seismic facies analysis, and fault definition. By interactively decimating the data through opacity and subvolume detection techniques, individual fairways and prospects can be described and evaluated. Co-rendering amplitude with other seismic attribute volumes allows rapid calibration to well data and identification of attribute combinations that effectively delineate exploration and production parameters, providing effective input to reservoir characterization ( Figure 1 ).

The essence of modern data visualization is the opportunity to view many classes and types of data rapidly and seamlessly in a machine-independent manner. The use of 3D visualization is independent of user interpretation, maintaining objectivity in the project evaluation. 3D visualization also retires the “2D paradigm”, where all interpretation and data presentation occurs on paper, poster, or monitors. Data visualization, while commonly portrayed in large visualization rooms employing expensive hardware, begins rather with the simplest question of “what if…?” in the interpreter’s mind as he or she works at more conventional workstations. The key to visualization is to translate that question rapidly into a working model, which can be constructed and evaluated in realtime by a technically integrated staff. Visualization allows for rapid evaluation of work programs; it is now possible at the onset of a project to review the data, identify prospective regions or reservoir trends, assess key technologic challenges, and determine an efficient work direction, all in the course of an afternoon.

We demonstrate these techniques by displaying workflows and examples from 3D prestack depth-migrated seismic volumes in the deepwater Gulf of Mexico and other deepwater basins. Examples of full-volume description of allochthonous shallow salt bodies, use of supra-salt sediment geometries to unravel complex shallow salt remobilization history, identification and 3D mapping of channelized and fan-form sediment intervals, and mapping of probable field extent utilizing calibrated seismic attributes will be displayed in both images and animations.

Biographical Sketch:

Lou Liro is a senior geologist for Veritas Exploration Services in Houston. He has over 20 years of experience in exploration and field development. Prior to Veritas, Lou worked in geophysical and geologic research units, domestic and international exploration, and international development for a major oil company. His specialties are reservoir stratigraphy, salt tectonics, and petroleum systems evaluation. He has published and presented over 50 papers on sequence stratigraphy, salt tectonics, and workstation visualization and has taught courses in sequence stratigraphy and basin evaluation.

For more information contact Mr. Liro at Veritas DGC, 10300 Town Park, Houston, Texas 77072, telephone: 832 351-8950, fax 832 351-8775, and email: louis_liro@ veritasdgc.com .

University of Houston Geoscience Alumni Association Lunch Meeting

"Hickory Field: Integrated Technologies Revitalize a Sub-salt Prospect"

UHGAA Web Page

Abstract:

The integration of improved seismic technologies and new geologic structural and stratigraphic models can often revitalize a prospect. This is a case history of the Hickory subsalt prospect in offshore Louisiana where 3-D raytrace modeling, new geologic structural and depositional models, and improved seismic processing techniques were employed. They developed a prospect which when drilled became Hickory Field.

In 1994, Anadarko and Phillips drilled the Teak prospect, which was a non-commercial subsalt discovery. Initial mapping showed the Hickory prospect to be a synclinally separated look-alike, with little potential for better sand development.

Improvements in seismic imaging, notably a 3-D prestack depth migration, allowed the base of salt to be accurately re-interpreted and showed the minibasin to be open to the northeast, toward the potential sand sources. A new depsitional model was developed in which deepwater turbidite sands were transported into the basin from the northeast, making Hickory prospect potentially more sand-prone. Empirical models supported the likelihood of increased sand presence as compared to the Teak area.

The improved seismic imaging also revealed several amplitude anomalies. A raytrace modeling study was undertaken to better understand these amplitude anomalies and therefore reduce exploration risk. Comparing modeled results to the existing 3-D prestack depth migrated seismic dataset enabled us to high-grade the initial location and make the exploratory well a success.

HGS International Dinner Meeting

"Structural styles of passive-margin deepwater provinces"

VENDORS:

WesternGeco will show example seismic lines crossing the deepwater slope provinces offshore Angola.
Contact info: John McTernan, (713) 689-6812 john.mcternan@westerngeco.com

Abstract:

Passive margins with salt or overpressured shale layers typically undergo gravitational failure above the weak detachment. The deepwater, distal provinces are dominated by contractional tectonics that balances proximal extension and downdip translation of the overburden. Failure is driven by a combination of gravity gliding above a basinward-dipping detachment and gravity spreading of a sedimentary wedge with a seaward-dipping bathymetric surface. Continued deformation is driven primarily by shelf and upper slope sedimentation, which maintains the bathymetric slope and the resulting gravity potential, and by increased basinward tilting. Deformation is retarded or halted by distal thickening of the overburden caused by the folding itself or by lower slope and abyssal sedimentation. Differences in deepwater deformation along various passive margins, such as the northern Gulf of Mexico or offshore west Africa, can be explained in part by differences in sedimentation, loading subsidence, thermal subsidence, and cratonic uplift.

Salt is a viscous material with no effective strength, whereas shale is a frictional material whose strength depends on the amount of overpressure. This rheological difference has several important ramifications. First, salt-cored folds are generally symmetrical with only minor faulting, while shale-detached foldbelts typically comprise asymmetric fault arrays with multiple detachment levels. Second, deformation above salt usually occurs immediately, beneath only a thin overburden, whereas shale-based deformation does not happen until there is a sufficient thickness of sediment to create overpressured conditions. Third, the location of salt-cored folds is controlled by the basinward pinchout of the salt, the toe of the slope, and thickness variations within the original salt layer, while the location of shale-detached deformation depends largely on the variable build-up and release of overpressure over time.

Salt can also reduce the gravity potential of the failing margin in other ways. The bathymetric slope can be decreased by proximal subsidence into salt and distal inflation of salt. The inflated salt, as well as existing diapirs or salt walls, can be squeezed laterally, thereby accommodating significant shortening. This, in turn, drives further diapirism and/or lateral salt extrusion. Extruded salt may amalgamate to form extensive salt canopies, so that subsequent gravitational failure may take place largely on shallow, allochthonous detachments rather than on the autochthonous salt level.

Biographical Sketch:

Mark G. Rowan, an authority on Salt Tectonics and the instructor for AAPG’s "Practical Salt Tectonics" school is a consultant in Boulder Colorado.

Mark received a B.S. from CalTech in 1976, an M.S. from Berkeley in 1982, and a Ph.D. in structural geology from the University of Colorado at Boulder in 1991. He spent 3 years at Sohio Petroleum Co. in Denver (1982 to 1985), four years at Geo-Logic Systems in Boulder (1985-1989), and three years at Alastair Beach Associates in Glasgow, Scotland (1989-1992). He then returned to the University of Colorado, and in 1996 he was appointed a Research Assistant Professor and headed up a large industrial research consortium investigating Gulf of Mexico salt tectonics. Mark left this position in 1998 and founded his own company, where he consults and teaches for industry and conducts research on salt tectonics. He is widely published having authored or co-authored over 40 papers and 75 abstracts.

For more information contact Dr. Rowan at: Dr. Mark G. Rowan , Rowan Consulting, Inc. , 1633 D 4th St. , Boulder, CO 80302 , tel - (303) 545-9437 , fax - (253) 541-1877 mgrowan@qwest.net

Posters:

Poster #1
Paleogeography of the pre-salt and salt basins of the Angolan continental margin
by Al Danforth, Steve Henry, and Vitor Abreu

Poster #2
Exploration in Syn-rift versus Post-rift Salt Basins of West Africa: Are There Significant Differences?
by Gabor Tari, Jim Molnar, Paul Ashton and Richard Hedley

Gulf Coast Association of Geologic Societies & Gulf Coast Section of SEPM present the

51st Annual Convention

Hosted by the
Shreveport Geological Society

Information:

Visit the GCAGS Web site www.gcags.org

The theme of the 51st annual convention is Odyssey to Success.

For over a hundred years, geologists have been on a long wandering journey of exploration and discovery that has led many to the Gulf of Mexico. Come and join us in sharing your odyssey for knowledge and achievement.

North America Exploration Dinner Meeting

"Reexamination of Late Jurassic Reef Building in the East Texas Basin; A Maturing Gas Play"

Abstract:

In 1993, Marathon Oil Company drilled the MOC Poth #1 near the western margin of the East Texas Basin. The well was completed in an Upper Jurassic reefal buildup approximately 350 feet thick. This outstanding gas well discovery kicked off a new gas play in a basin with a long history of extensive exploration. The depositional model in use at Marathon for their several reef discoveries can now be reexamined using additional information provided by 100 wells during 7 years of exploratory drilling. Workers can now focus on the identification of conditions favoring optimal reef growth and porosity development in Upper Jurassic reefs.

A faulting episode at or near the end of Gilmer time dislocated the carbonate ramp and effectively reshaped the shelf margin and basin. The topography created by this faulting event proved advantageous for reef growth and facilitated clastic sediment bypass into adjacent synclinal troughs. Evidence indicates that this faulting episode post-dated deposition of the Gilmer (Cotton Valley) Limestone and predated any significant Bossier deposition. Seismic data shows slide blocks composed of Gilmer Limestone were carried basinward. Deposition of the Lower Bossier shows no evidence of disruption by the décollement faulting, but does exhibit draping over fault toes of Gilmer blocks.

Derivative maps of paleogeographic surfaces were generated to identify the trend of the reef tract. They also served to underscore the value of sediment traps that protected coral reefs from the influx of clastic sediment shed from the near-by shelf. The highly developed, thickest, microbially bound, coral dominated, reefal buildups are positioned near the western margin of the East Texas Basin.

In 1998 Clayton Williams Energy, Inc. reinvigorated and expanded the Jurassic Reef play by stepping out 35 miles southwest of Marathon’s Riley Trust discovery to drill a successful reef wildcat. Limits of the play have yet to be defined.

Biographical Sketch:

Ed Norwood attended Potomoc State College and West Virginia University, receiving his Bachelors and Masters degrees from WVU in 1956 and 1957. He has worked as a Petroleum Geologist for 43 years in the employ of several companies starting with Phillips Petroleum Co and Pennzoil Company and more recently, Marathon Oil Company and Clayton Williams Energy. Ed's range of experience spans several basins including the Alaskan North Slope, The Appalachians, California, the Gulf Coast and the East Texas Basin.

HGS Emerging Technology Dinner Meeting

"E-Business: What’s the Big Deal?"

Abstract:

The author will discuss the benefits and advantages of the various kinds of e-business web sites, including:

The surviving dot-coms in the upstream oil and gas sector will be compared to the dot-bombs, and forecasts and quotes from major e-business players will be shared. A list of handy e-business Web sites will be given as a handout.

Biographical Sketch:

Jeanne Perdue is Senior Technology Editor of Harts E&P magazine. After receiving her BS degree in chemistry at the State University of NY at Albany, she went to work for Texaco in the Bellaire research laboratories testing oils and rock cores. Jeanne ran her own technical marketing company called JuMPstart Ventures prior to joining Hart Publications in 1996. Jeanne has been very active in the Society of Petroleum Engineers. She was the first woman to be appointed Review Chairman for the SPE Reservoir Engineering journal, she helped develop the SPE MasterDisc CD-ROM and SPE Magic Suitcase, and she currently chairs the Gulf Coast Section’s Community Services Committee.

HGS General Lunch Meeting

"Shanghai Field, Expanded Upper Yegua Trend, Texas Gulf Coast: Unexpected Reserves and a Distinctive Fault Style Defined by 3D Seismic "

Figures 1-5

Abstract:

As presented in 3-D Seismic Case Histories from the Gulf Coast Basin: GCAGS, 1998, p. 283-299.

A 3-D seismic survey resulted in efficient drainage by a directionally drilled well of a previously unrecognized, 80-acre structure on trend with 1980s production from Upper Yegua reservoirs at Shanghai Field.

Upper Yegua deltaic sandstones form a wedge that thickens into the Shanghai Fault. The top of the wedge (D-1) forms a series of downthrown closures transitional to rollover anticlines, with normal southward dip to the south. The base of the wedge (E-1) dips north into the fault, but is upturned into the main fault in various places, forming a series of “flaps” with apparent normal drag. The D-1 highs overlie the E-1 flaps. The structures were formed by differential movement along the fault plane-differential stickiness-during and after Upper Yegua deposition.

History

Shanghai Field (Wharton County, Texas) lies in the Jackson-Wharton Fairway of the Expanded Yegua Trend (Ewing and Fergeson, 1989, 1991).

Ladd Petroleum and Venus Oil developed four stacked Upper Yegua reservoirs at Shanghai Field (D-1 shallowest, D-3, D-5 and E-1 deepest) in 1985-1986 (Hart and others, 1988; Parker and Swenson, 1989). Eleven completions in six wells yielded 24.6 BCFG and 814 MBC from some 250 acres.

In December 1986, Ladd discovered Shanghai East Field in the same Upper Yegua sandstone sequence downthrown to the Shanghai fault, two miles east of the original field. Two wells were drilled. The first well was completed in the E-1 sandstone and the second well produced from the D-series sandstones. The two wells produced 3.3 BCFG and 196 MBC by the end of 1994.

Venus discovered Lower Yegua gas pay beneath the old field in 1993. To develop the Lower Yegua, Venus acquired with others a 9.8-square-mile 3D seismic survey. As a by-product, we found a new untapped 80-acre structure. We also identified the structural style of the Shanghai Field and can speculate on its origin.

Shanghai Field Structure

Seismic reflectors at the shallower D-1 and deeper E-1 levels clearly define the Yegua 25 wedge of deltaic sediment downthrown to the Shanghai Fault. At D-1, the field shows a weak rollover closure but is primarily a downthrown closure. The D-1 “peak reflector” dims in association with production ( Figure 1 ). At E-1, distinctive flaps of upturned sediment underlie the shallower closures, coming out of a tight syncline lying near the fault ( Figure 2 ). Where there is a productive field, the E-1 shows a dip reversal from reverse to normal dip adjacent to the Shanghai Fault ( Figure 3 ). Between fields, the E-1 dips directly back into the fault with no reversal ( Figure 4 ). The E-1 reflector also dims within the productive area. The intermediate, thick D-3 and D-5 sandstones show strong amplitude related to the original gas-water contact.

The Henry Closure

Seismic characteristics identical to the productive Shanghai Field were found on a small (80-acre) structure less than a mile east along the Shanghai Fault between Shanghai Field and Shanghai East field. The structure appears to be identical though smaller than the Shanghai Field (downthrown closure at D-1, flap at E-1) and similar to the Shanghai East Field. Bright spots related to fluid contacts in the D-3 and D-5 zones were imaged, as well as dim spots in the D-1 and E-1 ( Figure 5 ). The structure migrates along the fault plane, so that a vertical well could not efficiently develop the four anticipated pays. Therefore Venus planned a directional well which would penetrate the sandstones at an angle of 50° from the vertical.

The #1 Henry well discovered 314-368 ft of gas column with 52-127 ft of high-quality net pay distributed in five zones at the depths predicted from the seismic survey. The well is anticipated to produce over 4 BCFG and 300 MBC.

Origin of the Upper Yegua Structures

The Shanghai chain of fields form a distinctive series of downthrown closures within the depositional wedge of the Upper Yegua, underlain by flaps of sharply tilted rocks in the lower part of the wedge. In the flaps, dip is a sharp normal drag, compared with the reverse drag nature of the wedge base elsewhere. This implies that the expansion of the Yegua 25 section is lowest over the structural crests and greatest between and downdip of these crests.

Gulf of Suez normal faults show a similar evolution from local normal to regional reverse drag (Gawthorpe and others, 1997). In areas where expansion takes place without the fault penetrating to the free surface, normal drag develops as a “growth fold” over the buried fault. When and where the fault penetrates to the surface, the usual reversed-drag develops, with thickest accumulation occuring against the main growth fault.

The same mechanism may apply at Shanghai. Along parts of the fault during Upper Yegua deposition, the fault “stuck” and did not break the seafloor, and overall subsidence due to the regional faulting formed a growth fold, now seen as flaps of normal drag sediments. Later, these imperfections were smoothed out, and reverse drag formed the main wedge of Upper Yegua sediment.