December, 2001
HGS Meetings

HGS Joint Dinner Meeting:
HGS General and North American Exploration Group

"Physiographic Controls on Submarine Fan Development Within Depositional Sequences"

Vendors Corner :

Abstract:

Depositional sequences with distinct depositional relief can occur on the craton and continental shelf, as well as along the continental margin. This depositional topography can occur along sequence boundaries (erosional), within sequences (constructional), or as abandoned (relict) physiography. Detailed analysis of the depositional topography associated with sequences deposited in a variety of tectonic settings reveals that neither the presence of depositional relief or proximity to the continental margin explains basin-floor fan development within sequences. However, in the data sets studied the magnitude of the depositional relief along sequence boundaries can be used to explain and predict basin-floor (low-stand) fan development within sequences.

Integration of published seismic, well-log, and outcrop data from the Cretaceous and Tertiary of the U.S. Gulf and Atlantic coasts, offshore Australia, Norway, Russia, as well as the Triassic through Tertiary of the Alaskan North Slope, suggests that three distinct types of depositional sequences (Low-, Moderate-, and High-relief) can be defined. Low-relief sequences lack clinoform development. These sequences typically have slopes of less than 0.5 of a degree and depositional relief of less than 50 meters (150') along sequence boundaries. Low-relief sequences, which are common in cratonic basins, lack basin-floor low-stand fans. Moderate-relief sequences display distinct clinoform development, have slopes of 0.5 to 3 degrees, and display depositional relief of less than 150 meters (500') along sequence boundaries. These Moderate-relief sequences are common in foreland basins and on continental shelves. Moderate-relief sequences also lack low-stand fans. High-relief sequences display slopes of 2-5 degrees and depositional relief greater than 150 meters (500') along sequence boundaries. These High-relief sequences typically occur along the continental margins, but can occur in foreland and rift basins. High-relief sequences contain low-stand fans.

These observed relationships suggest that there is a Critical Shelf Break that controls slope stability or failure during relative sea-level falls. In basins where the depositional relief is less than the Critical Shelf Break, progradation continues during relative sea-level falls. The resulting Low- to Moderate-relief sequences lack basin-floor (low-stand) fans. In basins where the depositional relief is greater than the Critical Shelf Break, slumping, canyon formation, fluvial capture, and sediment bypass occur during relative sea level falls. The resulting High-relief sequences contain basin-floor (low-stand) fans. In the data sets studied, it appears that the Critical (Erosional) Shelf Break occurs with erosional depositional relief of 150-180 meters (500-600') in clastic systems.

Biographical Sketch:

Art D. Donovan received his PhD from the Colorado School of Mines in 1984. From 1984 to 2000, he worked for Exxon Production Research Company (EPR). At EPR, Art had the opportunity to conduct sequence and seismic stratigraphic studies from basins all around the world, as well as conduct fieldwork on almost every continent. During his time at EPR, he became a recognized corporate expert in seismic stratigraphy, sequence stratigraphy, and siliciclastic depositional systems. Over the last 17 years, Art has become a key player in the development of modern sequence stratigraphic theory, transferring this knowledge both within and outside of industry. The author of numerous publications on sequence stratigraphy, Art led field trips and short courses on sequence stratigraphy for AAPG, SEPM, GSA, and the London Geological Society. Presently he is the chairman of the SEPM Sequence Stratigraphy Research Group. Since December of 2000, Art has worked for BP, where he is the Sed/Analogue Global Network Leader. In this role he coordinates the stratigraphic discipline and champions issues associated with reservoir prediction and continuity, throughout the company.

HGS Environmental / Engineering Dinner Meeting

Texas Regulatory Awareness Committee (TRAC) -

HGS International Dinner Meeting

"Remaining exploration potential on the United Kingdom Continental Shelf (UKCS) - An Opportunity for US Independents"

Vendors

IHS Energy Group will be displaying a workflow poster that demonstrates how you can evaluate opportunities in the North Sea. From initial opportunity investigation to economic appraisal - IHS Energy Group has the application tools you need to make informed decisions for your North Sea Projects. A current North Sea activity map will also be displayed and a FREE map will be available for attendeees.
IHS Energy Group
Tel: +44 (0) 1666 501200
www.ihsenergy.com

PGS (Petroleum Geo-Services) as the holders of the largest 3D Multi-Client Seismic Library in North-West Europe are pleased to be able to demonstrate their "UK Central North Sea and Southern North Sea Mega Surveys" using a PGS proprietary state of the art 3D visualisation system - deskSeis . The total full-fold area of coverage of these 2 surveys is estimated to exceed some 55,000 km² and will be comprised of more than 150 original 3D surveys (when completed).

PGS is assisting several companies to meet their obligations under the DTI /UKOOA initiative on Seismic Data Release and Common Data Access (CDA). As a direct result, PGS now has agreements to broker and/or release over 45,000 km² of data from the UKCS. These recent developments create exciting opportunities for merging these 3D seismic databases to provide continuous full-fold 3D coverage over large regional areas.

The benefit of 3D is to enable companies to 'search for the subtle trap' in finding and developing remaining reserves. Additional benefits of a regional coverage of data are:

The availability of such large data sets also encourages companies to take new areas into consideration or to re-evaluate existing interests - much in line with the DTI initiative. It also provides potential new entrants to the UK with a cost effective seismic, well and interpretation package.

PGS (Petroleum Geo-Services)
Tel: (44) 1932 26 00 01
Email: europeinfo@pgs.com
www.pgs.com

Figures:

Abstract:

About 4000 exploration and appraisal wells (including re-spuds and sidetracks) have been drilled on the UK Continental Shelf (UKCS) over the past 37 years. These wells have resulted in more than 285 producing fields and another 168 significant discoveries. Almost 60% of the wells have been drilled in the largely oil-bearing northern and central North Sea (Fig. 1 ). The majority of the oil is found in sandstone reservoirs ranging from Devonian to Eocene in age, with the bulk of reserves in Jurassic strata (Fig. 2 ). About 20% of the wells have been drilled in the gas-bearing southern North Sea. Permian desert sandstones are the most prolific reservoirs there, with significant reserves also in Carboniferous and Triassic strata.

The peak of exploration and production activity occurred in 1990. Drilling activity then declined gradually to about 100 wells a year until the oil price collapse in late 1998. The success rate across the last 30 years has been a robust 35%, using a rolling five-year centered average. Six significant discoveries have been announced so far in 2001. Of these, PanCanadian’s Buzzard discovery has been described in a press release with reserves of 200-300 MMBOE, making it the largest discovery on the UKCS since Foinaven in 1992. Oil and gas production in the UK reached peak production in year 2000, and remains close to record levels at 5 MMBOE per day.

This paper will address the major new plays developed in the last decade, and summarise the opportunities for exploration in the next decade and beyond. The greatest potential for major new discoveries (Fig. 1 ) lies along the Atlantic Margin, where water depths are between 1,500 and 5,000 feet. The giant Foinaven and Schiehallion oil fields were discovered there in the early nineties, and both have Paleogene deepwater sandstone reservoirs. Significant discoveries will continue to be made in the relatively shallow waters of the mature North Sea oil and gas provinces. Most of these discoveries will be made in subtle stratigraphic and structural plays, requiring state-of-the-art technology to identify the best prospects and minimise the uncertainty.

The UKCS is located on the passive continental margin of the European plate, on the eastern seaboard of the North Atlantic. One of the most significant events in its geological history was a Late Jurassic phase of crustal extension along the axis of the North Sea, which led to the formation of major rift basins in the northern and central North Sea. A world-class source rock, the Upper Jurassic Kimmeridge Clay, was deposited within these rift basins and in many other parts of the UKCS (Fig. 2 ). Following Early Cretaceous collapse of the rift system, post-rift thermal subsidence led to hydrocarbon generation along the axes of the basins. Migration has been essentially vertical. Most of the traps were produced as a result of the rifting or post-rift faulting, but halokinesis of Upper Permian salt is locally also an important trapping mechanism. The Kimmeridge Clay source rocks have been largely eroded from the southern North Sea or are immature. The principal source rocks for the gas there are thick Westphalian coal seams preserved in the core of the basin.

The plays developed in recent years, and the focus of future exploration activity, are likely to be in the following:

Estimates of yet-to-find reserves on the UKCS are very subjective. The 2001 edition of the UK government’s publication “The Brown Book” predicts undiscovered reserves in the range 4-26 billion barrels of oil equivalent. These figures appear to be consistent with industry estimates, and could be viewed as somewhat conservative when compared to some! However, government and industry agree that the most prospective oil plays will continue to be in the central and northern North Sea, with parts of the Atlantic Margin providing the best gas opportunities.

In summary, the UKCS has proved to be a very successful exploration province in the last 35 years, with a success rate of 35% for its 4000 E&A wells. Recent successes have demonstrated that substantial reserves remain to be discovered in the mature North Sea. Exploration of the Atlantic Margin is still at a frontier stage, but this province has the potential to yield further giant oil and gas fields. * Note: full color versions of these figures are available at the HGS Website at http://www.hgs.org/meet1201.htm#intdin

Biographical Sketch:

Jim Munns B.Sc. Geology (London) is a Senior Geoscientist with the UK Department of Trade and Industry. He joined the DTI in 1999 following 20 years with Amoco in both technical and managerial positions. He has published several papers on various aspects of petroleum geology of the North Sea. Currently he is responsible for promoting international interest in the UKCS. He can be reached at the UK Department of Trade and Industry, Tel: 44 (0)20 7215 5079 Fax: 44 (0)20 7215 5070, email: jim.munns@dti.gsi.gov.uk

Posters:

Reserves Opportunities in the UK Southern North Sea
by Jim Hollywood, John Sneider and Bob Sneider