"The Virtual Oil Company: Capstone of Integration"
Date: Monday, November 6, 2000
Place: Westchase Hilton, 9999 Westheimer
Time: Social 5:30 p.m., Dinner 6:30 p.m.
During the 1980s, visionary oil companies embraced new 3D seismic technologies to radically improve subsurface imaging. Today, a new breed of "virtual energy companies" is beginning to explore more collaborative business models, leveraging new global information technologies to re-invent decision making across the entire E&P lifecycle.
In a truly collaborative model, the oil company would own both the reservoir and associated earth model throughout the life of the asset. The service company would provide the information systems and technical support needed to create and store the earth model. It might even have controlled access to that model in real time. But the oil company would never give up ownership. It would remain the macro-level project manager by choosing which service companies to use and managing the interfaces among all the parties involved. By doing so, it would become a true virtual energy company.
Within this virtual company, all partners and service providers would maintain highly interactive and collaborative relationships at every stage of the lifecycle, from early exploration through late production. To the casual observer, it might even be difficult to identify which individuals work for the service company and which work for the energy company. However, the underlying economies of knowledge would always be clear to the individuals themselves through access to and support of the particular decision-making processes associated with their home base.
Biographical Sketch:
Bob Peebler is Halliburton's vice president of e-Business Strategy and Ventures. He assumed this new post in May 2000 after serving as president and chief executive officer of Landmark Graphics Corporation since 1992. Mr. Peebler held a variety of executive positions at Landmark including chief operating officer and president of the company's seismic products division. Before joining Landmark, Mr. Peebler worked in the oil field services industry for 18 years. He holds a BSEE degree from the University of Kansas. He was instrumental in Landmark's strategic acquisition and integration of leading geoscience and engineering software companies, including Zycor, Advance Geophysical, Stratamodel, Munro Garrett, GeoGraphix, Western Atlas Software and others. These acquisitions provided the technological innovations that underlie Landmark's strategy of delivering the industry's broadest range of integrated information solutions for finding and managing oil and gas. Mr. Peebler is recognized as an industry visionary. He is a widely published author and speaker about the information technology trends transforming the exploration and production industry. He is acknowledged as being a driving force behind The Quiet Revolution, a major study on how information technology is transforming the upstream oil and gas industry. His latest publication, entitled The Virtual Oil Company, outlines a visionary model for optimizing the whole value chain associated with oil and gas reservoirs. He is a member of the "25-year Club of the Petroleum Industry" and is on the board of directors for Input/Output, Inc., Synectics Technologies LLC and Sheltering Arms Senior Services. He is a member of the University of Houston President's Advisory Board on Energy, and serves on the editorial advisory board of Petroleum Engineer International. Formerly, he served on the boards of directors of Landmark Graphics Corporation, Drilex Systems, Inc, and the Houston Museum of Natural Science.
Geological Registration: Two formal speakers as well and an open mike discussion
Date: Thursday, November 9, 2000
Place: H.E.S.S. Conference Center, 5430 Westheimer Rd. (refer to map ), just West of the Galleria.
Time: Social: 5:00 - 5:30 PM, Dinner 5:30 - 6:30, speakers will present from 6:30 until 7:00 with an open discussion thereafter
The scheduled speaker cancelled so we are holding a presentation on Geological Registration with two formal speakers as well and an open mike discussion. The speakers will be Dave Rensink, former head of the Registration commitee, and Dan Smith, former HGS President.
"Case History and Integrated Study of the West Cameron 76 Field, Gulf of Mexico Shelf- Big Reserves in the Expanded Marg A"
Note: New Location - Petroleum Club. Meal Cost increase to $25
Date: Wednesday, November 15, 2000
Place: The Petroleum Club, 800 Bell Avenue, Downtown. Valet parking is available.
Time: Social 11:15 a.m., Lunch 11:45 a.m.
Summary
The West Cameron Block 76 field consists of four blocks purchased in a 1988 Gulf of Mexico OCS lease sale. Originally mapped on 2D seismic data, the A-1 and A-2 wells were drilled, encountering 193 and 81 ft. of gas respectively. The field was then remapped utilizing 3D seismic data.
A 3D interpretation was made and four additional wells were drilled before an AVO study was completed. This study led to the drilling of the B-3 well, which became one of the keys to understanding the field. The B-3 was drilled into an expanded Marg A interval, with a gas-water contact common to the B-2. This and other information gained from the B-3, integrated with the reprocessed longer offset data, made field definition possible for the first time. The B-4 and B-5 wells were then drilled encountering the thickest pay column to date.
Introduction
The West Cameron Block 76 field lies in the Gulf of Mexico, 12 miles off the coast of Louisiana in 40 ft. of water. The field's development followed a classic approach yielding very favorable results. A prospect was identified on 2D spec seismic data and verified with additional 2D proprietary seismic data. 3D seismic was obtained and interpreted for a more detailed structural evaluation. As wells were drilled and the results were integrated with the seismic, a more accurate interpretation evolved. During this evolution, the appropriate technology was utilized to gain valuable information for defining the field. This classic approach has led to the latest geological and geophysical integration. Originally thought to be roughly 155 bcfe, the field reserve estimates now top 400 bcfe.
2D Seismic
A prospect was identified on the four blocks of the West Cameron Block 76 Field prior to the 1998 Gulf of Mexico OCS lease sale based on 2D spec seismic data. Proprietary 2D data were then acquired and the resulting interpretation indicated a faulted four-way structure downthrown to a large down-to-the- southeast fault (Fig. 1).
The four-way closure was common to the four blocks on the structural mapping. Sands in the area were found to be from an upper slope paleo environment with the Marg A mapped as the primary objective. In mid-1991, the #1 (A-1) was the initial exploratory well drilled. The well was directionally drilled under a shipping fairway into West Cameron Block 76. This discovery well targeted the crest of the Marg A structure and encountered 193 ft. of gas in three Marg A sands (Fig. 2) .
In early 1992, the #1 (A-2) was drilled into West Cameron Block 60 to help determine the size of the reservoir. This well encountered 81 ft. of gas in two Marg A sands. The "A" platform was set in 1992 and production commenced averaging 35 mmcfg per day from the two wells.
3D Seismic
The West Cameron Block 76 Field was then remapped utilizing newly acquired 3D data. The A-1 and A-2 wells exhibited conflicting sonic and density information. This conflicting information and the structural complexity made it difficult to draw conclusions on rock properties and seismic signature. In late 1993, the A-3 was drilled into West Cameron Block 61 near the top of the structure. The well targeted a bright seismic event at the Marg A level. The well encountered 152 ft. of gas in two Marg A sands. In early 1995, the A-4 well was drilled in a downdip position in an attempt to delineate the field. The well encountered 96 ft. of gas in three Marg A sands; however, these sands were evaluated as tight and nonproductive. The A-4 caused concern about sand quality downdip on the structure and delayed further development until late 1996.
The "B" platform was set adjacent to the "A" platform, and in October 1996 the B-1 was drilled into West Cameron Block 60. This well was drilled targeting the Marg A interval closer to the large down-to-the southeast fault on a structural nose in the hope of seeing a more expanded pay section. The well encountered 58 ft. of gas in two Marg A sands. In early 1997 the B-2 well was drilled into West Cameron Block 76, considerably south and downdip of the A-4 well. The well encountered 105 ft. of gas in two Marg A sands. A very expanded Marg A-3 sand section was seen with gas on water. The B-1 and B-2 wells were completed and placed on production. The field production increased to 55 mmcfg per day.
3D AVO
With numerous wells drilled, the necessary calibration was thought to exist to initiate an AVO analysis of the field. The work was completed in 1998 and with the exception of the B-1 well, the Marg A pay section exhibited a definite amplitude increase with offset. It was evident that a deeper interval downdip and south of the B-2 pays exhibited strong far offset anomalies. In 1998 the B-3 well was drilled targeting these deeper anomalies as well as the expanded Marg A pay section seen in the B-2. The deeper anomalies were false positives to hydrocarbons, but the well encountered 90 ft. of gas in two Marg A sands (Fig. 3) .
A water level common to the B-2 was seen in the very expanded Marg A-3 interval. Using an offset VSP, a very good synthetic tie was made through the Marg A interval in both the B-2 and B-3. The water level tied to a strong flat seismic event. The synthetic ties along with subsequent seismic work was done on the AVO full offset data volume. Because of much longer offset information (20,000 ft.), the AVO full offset data volume provided more continuous and clearer data necessary for doing yet another interpretation integrating the new well information. Using the AVO full offset data, the field was remapped. It became obvious that the Marg A-1 exhibited a distinct phase change that clearly defined the reservoir limits (Fig. 4) .
The Marg A-1 pay was mapped on a trough through the phase change downdip on a peak. The amplitude extraction provided a very good fit to the structure map, yielding an accurate areal extent of the reservoir. The Marg A-2 was not sufficiently resolved on seismic to map a continuous reflection. The Marg A-2 reservoir was defined using conventional subsurface data. The Marg A-3 flat spot also clearly defined its reservoir limits and could be demonstrated on all downdip sides of the field (Figs. 4 and 5) .
Also mapped on a trough, the Marg A-3 amplitude extraction brightened considerably where approaching and going through the flat spot. This is the area of seismic tuning along the downdip edge of the reservoir. The amplitude extraction exhibited a high amplitude band around the edge of the field which provided an excellent fit to the structure map (Fig. 6) .
Like the Marg A-1, the Marg A-3 amplitude extraction yielded a very accurate areal extent of the reservoir. In the expanded Marg A-3, the area of expansion was identified on seismic (Fig. 4). The top of the Marg A-3 to the water level within the expanded wedge was isopached and an average net-to-gross was used to complete a final net pay isopach.
Verification Through Modeling
A good tie between the seismic and the well control was critical to the understanding of this field. Figure 7 shows the tie between the B-3 well and the AVO full offset seismic data. This tie helped identify the common water contact and the expansion of the Marg 3 section.
To verify the structural and stratigraphic interpretation a 2D model was built. It follows a south-north transet through the field crossing the buried fault that expands the Marg A-3 and includes the Marg A-1 and Marg A-2 pay sections.
Rock properties for the model came from the well control (A-1 and B-3), with shear information provided by the dipole log run in the B-3 wellbore. The seismic field acquisition parameters were used in the model and 500 common source point gathers were ray traced. Rays were traced from the source to the reflectors to the receivers for all reflector curves. Only PP reflections were captured. The modeled shot records were then input to a processing flow that closely matched the one used in the AVO reprocessing. The final pre-stack time migration model exhibits many of the characteristics of the 3D seismic. (Fig. 8) . The common water contact brightening because of tuning is clearly visible, as are the phase changes going from wet sands to pay sands on the flanks of the structure. The model therefore verifies the interpretation of the seismic data.
Recent Development
In 1999 the B-4 well was drilled on the eastern downdip side of the structure for the same expanded Marg A-3 seen in the B-2 . The B-4 found 285 ft. of gas pay in the Marg A. This was followed by the B-5 well which encountered 298 ft. gas in three Marg A sands for the results were also consistent with expectations.
Conclusions
First of all, the success at West Cameron 76 Field illustrates that significant gas reserves remain to be found in the shallow waters of the Gulf of Mexico Shelf. Over 200 bcfe of reserves were added to this field in 1999. These results encourage us at Dominion to remain an active Shelf player. The study also shows that the geophysical response of a hydrocarbon accumulation can be quite complex. This complexity can be difficult to unravel even after drilling several wells in a field. However, using available technology with the proper integration of geology and geophysics enables us to achieve excellent interpretations for use in field development.
Acknowledgments
The authors thank Dominion Exploration and Production, Inc. for allowing us to present this data, along with BHP, Houston Exploration, and Ridgewood for their cooperation. We also wish to thank Fairfield Industries for allowing us to use the seismic data.
Figure Sumary:
Biographical Sketch:
Kevin Guilbeau is general manager, Offshore Exploration and Development for Dominion E&P, Inc. Kevin's responsibilities include both the Gulf of Mexico Shelf and Deepwater provinces. Kevin has over 19 years in the oil industry and has been with Dominion (previously CNG Producing Company) since late 1996. Prior to his position with Dominion, Kevin worked for Shell Oil Company for 15 years from 1981 through 1996 where he held a variety of positions in both the onshore and offshore regions. He was assigned to Shell's Deepwater business unit from 1990 to 1996 where he worked as lease sale coordinater and new ventures team leader. Kevin holds an MS degree in geology from the University of New Mexico and a B S in earth sciences from the University of New Orleans. He is a member of the American Association of Petroleum Geologists, Society of Exploration Geophysicists, New Orleans Geological Society, and the Houston Geological Society.
"The Prizes and Pitfalls of Becoming an Independent"
Date: Wednesday, November 15, 2000
Place: Jillian's, 7620 Katy Freeway
Northwest side of I-10 and 610, next to Edward's Cinemas. 713-263-0303
Time: Social 5:30 p.m., Dinner 6:30 p.m.
NeoGeos is pleased to announce our second dinner meeting of the year featuring HGS President Craig Moore of Bellweather Exploration and Robert Pledger, a Houston independent and president of Benchmark Oil and Gas Company. Craig and Robert will share their advice with those who have recently entered the industry on what it takes to be an independent, what to expect when you're on your own, and how to try to best plan your career to be successful. This will be an interactive discussion and there will opportunities to address both technical and business-specific issues.
Biographical Sketch:
Robert E. Pledger: BS geology, Lamar University, 1969; MBA business/finance, University of Dallas, 1973. Independent since 1977. President of Benchmark Oil and Gas Company, a 23-year-old Texas corporation. Experience in all phases of oil and gas including capitalization, operations, prospect generation, and purchase of producing properties. Areas of interest include the Gulf Coast, West Texas, Kansas, Oklahoma, Louisiana, New Mexico and California and internationally France, Tunisia, Peru, Australia, Argentina, Morocco and Spain. Prior employment includes Sun Oil Company, May Petroleum Company, General American Oil Company of Texas, and Shenandoah Oil Corporation. He has served as a consultant to numerous domestic and international companies. He has served as Chairman of the Houston Chapter of SIPES twice, on the National Board of Directors of SIPES from 1986 to 1989 and was Chairman of the National Energy Advisor Council in 1987. Currently, he is Chairman of the Houston Geological Society's Continuing Education Committee, an alternate delegate to the AAPG from Houston and liaison on the AAPG-DPA Education Committee and SIPES.
Craig Moore received his professional degree in geophysical engineering from the Colorado School of Mines in 1969. He started his career as a geophysicist with Texaco in Houston. In the summer of 1970, Craig was called into the Army Corps of Engineers, and he worked as an Engineer Staff Officer for the next two years at the Army's Topographic Command Headquarters in Washington, D.C. In 1972, upon release from the Army, Craig joined Gulf Oil Co. in Pittsburgh. His primary task at Gulf was to prepare integrated geophysical/geological regional studies for the company's Asian Operations. He later worked on domestic regional studies in Offshore MAFLA and the onshore Woodbine-Tuscaloosa trend. In 1978, Craig accepted a position as chief geophysicist with Natural Gas Pipeline Company of America. During this time, Craig coordinated geological and geophysical exploration activities in Natural's district offices in Houston, New Orleans, Midland, Oklahoma City, and Denver. He was instrumental in the discovery of several fields, most notably the field in Main Pass 151, offshore Louisiana. In 1980, Craig joined a newly formed exploration company, Trinity Resources, which had just acquired an interest in 33,000 acres in Burleson and Lee Counties in Texas. Craig's success in picking over 175 commercially successful Austin Chalk locations continued into the Edwards and Glen Rose formations, where he made the first commercial Glen Rose discovery south of the Fort Trinidad field. He also participated in the discovery of the Giddings Edwards field. During this period, Craig also generated and sold prospects along the Texas and Louisiana Gulf Coast, East Texas, and the Rocky Mountains. Trinity's exploration budget terminated in the fall of 1984, and Craig set up shop as an independent exploration consultant. Since that time, he has continued to consult, generating and evaluating exploration prospects, based in Houston.
"Real-time Geopressures While Drilling – Considerations and Case Histories"
Date: Thursday, November 16, 2000
Place: Westchase Hilton, 9999 Westheimer
Time: Social 5:30 p.m., Dinner 6:30 p.m.
The failure to accurately quantify geopressures (pore pressure and fracture gradients) at the wellsite for wells drilled in areas of high pore pressures can be costly, both in terms of well cost and human and environmental safety. This is an especially difficult problem for wells in deep water in areas of little known geology, where only surface seismic data is available for the prediction of geopressures. Often there is not sufficient resolution in the surface seismic data to accurately identify the depth of hazards such as shallow gas pockets and pressure zones.
This presentation describes the experience obtained in using a variety of types and kinds of real-time data collected at the wellsite, analyzed by several different models, all integrated together in a single computer system to quantify geopressures. Traditional real time measurements such as gamma ray, resistivity and drilling parameters are discussed, as are some of the newer measurements such as sonic, pressure while drilling and seismic while drilling. The experience has shown that where individual porosity indicators, such as resistivity, are used alone they can be misleading and problematic. Resistivity, for example is affected by environmental factors such as temperature and salinity, and sometimes gives a false pressure indication in areas where those factors prevail. However, when resistivity data is used in combination with sonic data, and perhaps multiple models are used for used with each, the variety of results significantly enhances the ability to quantify results. When other geopressure indicators are added in, such as gas volumes, drilling data (drilling exponent), etc., the picture becomes even clearer. With the benefit of VSPs and/or seismic while drilling, it becomes possible to "look ahead of the bit" to further identify hazards. So while each measurement on its own can provide sometimes misleading and hard to interpret results, the integration of several of them together can give a much more clear picture.
Several case histories will be presented that illustrate application of this technology in areas that range from the Gulf of Mexico, to the North Sea and the South China Sea. Case histories will include the use of available data to predict accurately the pressures ahead of the bit, and the successful transferring of experience and calibrations from one area to another.
Biographical Sketch:
Founder and President of Knowledge Systems and Geopressure Systems, Mr. Bridges has been involved in the design, development and support of engineering software for more than 30 years, founding his first software company in 1969 and seeing it go public in the 1980s. He founded Knowledge Systems in 1985 to develop knowledge based software applications for the oil and gas industry. Mr. Bridges designed the DrillWorks/PREDICT software system. Funding for development of the system was provided by an industry consortium of several major oil companies organized through the Drilling Engineering Association.
DrillWorks/PREDICT was introduced as a commercial software product in 1991, and has since become the most widely used software system in the world today for geopressure analysis. In 1997, Geopressure Systems was formed as a division of Knowledge Systems to provide services at the wellsite to monitor geopressures while drilling using DrillWorks/PREDICT in such areas as Gulf of Mexico, Trinidad, West Coast of Africa and the South China Sea. Currently he is managing another industry consortium project through the Drilling Engineering Association to Develop an Improved Methodology for Pre-Drill Geopressure Prediction for Wells in Deep Water. He holds a BS and MS in Civil Engineering from Texas A&M University.
"Chemistry: An Odyssey of the Mind and of the Eye"
Date: Thursday, November 16, 2000
Place: Crown Plaza Hotel, 2222 West Loop South
Exit Loop 610 at San Felipe and proceed on the service road to the Crown Plaza Hotel (if exiting north, go under the freeway and onto the service road). Ground level and garage parking are available.
Time: 6:30 Social Hour, 7:00 Dinner, 8:00 Presentation (free to all and open to the public)
"AFRICA'S VAST PETROLEUM SYSTEMS." This is the Second Second Annual Robert E. Sheriff Lecture Series , Sponsored by the U of Houston Geosciences Alumni Association in association with the Houston Geologic Society
Date: Monday, November 20, 2000
Place: Westchase Hilton, 9999 Westheimer
Time: Social 5:30 p.m., Dinner 6:30 p.m.
Macgregor and Cameron (2000) showed that 98% of Africa’s petroleum reserves could be assigned to one or other of seven groups defined by: source rock, age, facies and tectonic setting (Fig.1) . I here summarize the tectonic history of Africa over the past 600 My because it provides a dynamic framework for the appreciation of the roles of the seven groups (Burke, 2000).
Assembly of Gondwana and Collapse of the Mountains Built During Assembly
Africa’s geological history began with the final assembly of the great continent of Gondwana about 600 million years ago. What is now Africa formed most of the newly-aggregated western part of the giant, 80 M sq.km., continent. In western Gondwana continental and island-arc collisions at the end of Precambrian time built up a mountainous area five to ten times more extensive than that presently occupying central Asia. The collapse of a part of that huge mountainous region from elevations comparable to those of today’s Himalaya and Tibet extended an area of 5 M sq. km in North Africa and Arabia to 10 M sq. km in an episode of tectonic escape. Widespread rifts halved the thickness of the continental lithosphere as it extended. Thermal subsidence over the rifted and extended continent led to the formation of a composite long-horn basin that accommodated the deposition of Afro-Arabia’s oldest great reservoir rocks: The North African and Arabian Cambro-Ordovician Quartz-Rich Sandstones (the NAACOQRS) of Algeria, Tunisia, Libya and the Arabian peninsula. These reservoirs form parts of what appears to have been the largest body of sandstone ever deposited on continental crust ( Burke,1999 ). Source rocks of Silurian age (Fig.1) have generated fluid hydrocarbons that have charged parts of the Cambro-Ordovician reservoirs at various times during the past 400 My.
Continuing thermal subsidence over North Africa and Arabia until about 300-250 Ma accommodated an average total thickness of 5 km of almost carbonate-free Paleozoic sedimentary rocks (Boote et al.1998 fig.3-8). Nowhere else in the world is carbonate-poor sedimentary rock cover so thick on a continental scale. The gradual and declining thermal subsidence which permitted this exceptional thickness of continental cover rocks to accumulate was rudely interrupted at about 300 Ma by the beginning of 100 million years of intra-continental tectonic unrest following the collision of Gondwana with Laurasia.
Assembly of Pangea
The collision that assembled Pangea contrasted with both the collision that had assembled Gondwana and the presently active collision of India with Asia. The contrast lies mainly in the extremely widespread distribution of intra-Pangean deformation associated with the collision. In North America we recognize the effects of the Pangean-forming collision in intra-continental tectonic phenomena such as the inversion of the Southern Oklahoma rift. Contemporary events on the global scale include the inception of rifting in the North Sea, the establishment of the Gondwana rifts of India and the beginning of rifting off the north-western corner of Australia and in the Perth basin. If we add Permo-Triassic rifting under the West Siberian basin and in Antarctica we can see that 60 % of the area of the world’s continents (100 M sq. km out of 160M sq.km) remote from the immediate vicinity of collisional mountain-belts was affected. Africa was no exception to these effects. The tar sands of Madagascar represent an organic rich accumulation in a rift formed during this time. The collapse of the mountains formed in the Pangean collision was achieved by rifting in the familiar Newark rift system and in North Africa rifts. A composite long horn basin over those rifts in Tunisia and Algeria is occupied by the "Triassic argillo-greseux de l’interieur (TAGI)". Those rocks accumulated in a sub-aerial basin below sea level that was catastrophically flooded by sea water c.200 Ma in an event which generated a seal of extensive Liassic age evaporites.
A change in Africa’s tectonic style at 200 Ma
For the past 200 My Africa’s tectonic development has contrasted with that of all the other continents. Africa has been dominated by the consequences of interaction with mantle plumes. Mantle plumes, whose existence is recognized in topographic and volcanic phenomena at the Earth’s surface, represent hot material rising from the underlying mantle. Plate-margin phenomena around Africa since 200 Ma have been closely linked to plume activity and only to a minor extent to plate boundary convergent and mountain building events. One reason for this unusual development has been that the slab-pull force, which is the dominant force governing plate motion, that has been applied to the African plate has been small. Consequently Africa has moved only slowly (Fig.2) facilitating interaction with the underlying hot mantle. Because no cold subducted slabs of lithosphere have penetrated under Africa during the past 250 My the deep underlying mantle has escaped refrigeration. Conduction from the core has gradually heated a large volume in the sub-African deep mantle. During the past 200 My half a dozen giant plumes which have extracted heat from that deep-seated volume have risen to the surface.
The eruptions of two of those plumes, the Karroo plume, at 180 Ma, and the Afar plume, at 30 Ma, have played important roles in the development of Africa’s petroleum systems. The eruption of both plumes coincided with the initiation of a spectacular range of plate-wide phenomena including the generation of basins and swells, episodes of intracontinental rifting, and widespread intraplate igneous activity. These outbreaks have been attributed to the arrest of the slowly-moving overlying plate (Fig.2) and the consequent establishment of a distinctive pattern of shallow upper-mantle convection. The Karroo plume eruption at 180 Ma was also associated with the immediate departure from Africa of two continents: North America and" Greater Antarctica", which consisted of Antarctica, Australia, India, Madagascar and the Seychelles. Those departures represented responses to a failed attempt by the Karroo plume to pin the whole of Pangea. The two departing continents proved unpinnable because they were subject at the time to strong slab roll-back forces which pulled the continents away from Africa at existing rift sites. The Central Atlantic and the Indian Oceans began to develop from those rifts.
A new population of rifts began to form within the interior of Residual Gondwana ( Africa, Arabia and S.America ) at various times between 180 and 140 Ma while Karroo-plume-induced pinning persisted. Currently exploited petroleum systems of Central Africa, Sirte, Yemen and the South Atlantic stem from Cretaceous and Late Jurassic source rocks deposited in rifts of this population (Fig.1) . The petroleum potential of others of this population of rifts, for example on the shores of the Gulf of Guinea and the Bulge of Africa is being actively pursued. Eruption of the Tristan plume on the site of the future South Atlantic at 130 Ma unpinned Residual Gondwana. South America began to rotate away from the Afro-Arabian continent. Until 115 Ma a barrier formed by the Tristan plume hot-spot track prevented ocean waters from spilling into the northern South Atlantic. Balance-filled lakes at 3 km below sea level in a subaerial depression on top of oceanic crust were the site of deposition of source rocks, possibly also reservoir rocks and finally, when the ocean waters did spill into the depression, of the deposition of Late Aptian evaporites.
A Quiet Time
For the most part Afro-Arabia was a tectonically quiet continent between 125 Ma when the South Atlantic began to open and 30 Ma when the Afar plume erupted. The African plate grew steadily while rotating slowly anticlockwise about an internal pole close to 7N 11E (Fig.2) . Rifted margins of the continent followed the classic progression from rift-fill deposition through subsiding carbonate banks to siliciclastic deposition with integration of river systems in that last stage from "numerous and short" to "few and long". Longer rivers of Africa during the quiet time included: the Sirte feeder, the Tan-Tan,the Benue, the Casamance-Senegal, the Orange,the proto-Volta the proto-Ogoue and the Zambezi. By 40 Ma Afro-Arabia was a low-lying, generally humid continent with little relief and a well-integrated drainage system. A remarkable perturbation of the quiet evolution of Afro-Arabia had happened during Santonian times (85 Ma) when folding and thrusting over half the area of the continent broke the peace. This event which produced its most spectacular results in the Syrian arcs and in the lower Benue rift is attributable to arc collision with the east coast of Arabia. That collision, which is best recorded in Oman, not only caused widespread deformation within the continent and on the ocean floor of the African plate but led to the rotation of the direction of Africa’s convergence with Eurasia from almost due east to almost due north.
The Past 30 Ma: Erosion of newly formed swells
At 30 Ma the Afar plume erupted raising the local base of the lithosphere so that plate-rotation was again arrested (Fig.2) . Immediately a new pattern of shallow-mantle convection was set up and another episode began in which the consequences of plate-pinning dominated tectonics. The familiar active plate-wide basin and swell structure of Africa was established, the East African rift system developed by rift-propagation from a rift star that formed over the Afar plume and volcanic activity, related to the new shallow-mantle convection, broke out on the crests of 60 % of 75 newly formed topographic and structural swells.
Deposition of sediments eroded from the newly formed swells on the continent has dominated the development of African Petroleum systems during the past 30 Ma. Completely new river systems notably the Nile and the Congo have formed and older systems including the Niger-Benue, the Orange and the Zambesi have been radically changed.
Sedimentary deposition around Africa during the past 30 Ma, although primarily dependant on the erosional response to the uplift of the new swells, has also been strongly influenced by climatic change. The ice-sheet of East Antarctica attained continental-scale dimensions at the end of the Eocene (34 Ma). World-wide this led to about a 50 m drop in sea level and to the formation of new submarine canyons. Around Africa the consequences of swell elevation, beginning at 30 Ma, and glacially controlled sea level lowering, at 34 Ma, can seldom be separated but submarine canyon development around Africa appears to me have been more spectacular than on other Atlantic-type continental margins. I would explain the canyon development around Africa as the result of superimposition of the effects of eustatic and tectonic processes since 30-34 Ma. The other way in which climatic change has influenced Africa’s petroleum systems during the last 34 Ma has been in forming deserts and relatively dry areas from which there has been only limited erosion. The Benguela current is a cold ocean current that began to flow northward past the Cape of Good Hope and along the west coast of Africa when the East Antarctic ice-sheet fomed at 34 Ma. Westerly winds crossing the Benguela current reach Africa dry. This has been a primary control on erosion in southern and eastern Africa. The reason that the swells in southern and eastern Africa are higher than those in northern and western Africa is that although uplift has probably been comparable there has been much less erosion in the south and east. The driest large areas in the world in the Saharan and Arabian deserts have only become dessicated since 3 Ma when Northern hemisphere glaciation got underway. The Ahaggar which rises to nearly 3 km in the middle of the Sahara desert has had 4 km or more eroded from its crest during the past 30 My. Much of that material now lies in the Niger delta. By contrast erosion of southern Africa has been relatively limited during the past 30 My. The Orange delta was a much more active delta during the Late Cretaceous than it is now.
The Niger and Nile deltas and the Congo fan are places at the edge of the African continent where petroleum systems involving Tertiary sources, reservoirs and seals are most important. Newly deeply-buried Cretaceous source rocks are also important in all those areas. A crude rule of thumb might be:"Places around Africa where the post-30 Ma sediment pile has contributed to burying organic rich Cretaceous rocks to a depth of more than 3 km should be considered as potentially prospective".
Conclusions
Africa’s petroleum systems can be considered in relation to tectonic phenomena:(1) the assemblies of Gondwana and Pangea (2) Collapse of mountain belts built during those assemblies (3) the slow motion of Africa with respect to the underlying mantle. (4)two episodes of plate arrest related to the eruption of the Karroo and Afar plumes. The erosion of swells formed in response to the eruption of the Afar plume at 30 Ma has been responsible for generating the environments in which the greatest part of Africa’s present reserves are to be found (Fig.1). Climatic influences on the African environment during the past 30 My have been important.
Figure Summary:
Figure 2. Slow Movement of Africa Over the Past 300 Million Years The position of Africa with respect to the equator and the zero meridian estimated from paleoenvironmental, apparent polar wander and sea-floor magnetic data for the past 300 My. Africa has moved slowly because it has not been pulled by subducted slabs. Movement was minimal from 180 to 13
References
David Boote, Danny Clark-Lowes and Marc Traut, (1998) Paleozoic petroleum systems of North Africa in Spec. publ. Geol. Soc. 132 Petroleum Geology of North Africa ed. Macgregor, Moody and Clark-Lowesp.7-68.
Kevin Burke (2000) Africa’s Petroleum Systems: Four Tectonic Aces in 600 Million Years in" Petroleum Systems and Evolving Technologies in African Exploration and Production". Geological Society of London and Petroleum Exploration Society of Great Britain.
Kevin Burke (1999) Tectonic significance of the accumulation of the voluminous early Paleozoic reservoir-containing quartz-rich sandstones of North Africa and Arabia: Houston Geological Society Bulletin v.41,no.7,p.11-13
Duncan Macgregor and Nick Cameron (2000) An Overview of the Petroleum Systems of Africa in " Petroleum Systems and Evolving Technologies in African Exploration and Production" Geological society of London and Petroleum Exploration Society of Great Britain.
Biographical Sketch:
Kevin Burke was born in London, England a few days after the collapse of the stock market in 1929. He received B.Sc and Ph.D degrees from London University in the 1950's and worked as a geologist with the British Geological Survey and in Universities in Africa, Asia and the Caribbean until 1970 when he went to Toronto to work with Tuzo Wilson. Between 1973 and 1983 he worked at the State University of New York in Albany with Bill Kidd, Celal Sengor and John Dewey.
Kevin came to Houston in 1983 to direct the Lunar and Planetary Institute (1983-1988) and to work in the University of Houston. Kevin's research concentrates on tectonics " the large scale evolution of planetary lithospheres" but he gets less done in that field than he might because he edits journals first TECTONICS and now THE JOURNAL OF ASIAN EARTH SCIENCES and gets involved in international organizations like the SCIENTIFIC COMMITTEE ON THE LITHOSPHERE.
Kevin has newly reduced his teaching commitment to one semester a year at the University of Houston and is now spending part of his time at the Carnegie Institution of Washington in the hope of getting more research done especially on Africa, Asia and the Caribbean. Kevin's mantra is "All geology is regional geology".
Posters on current research activities and Synopsis of presentations from the AAPG, GSA, SEG, GCAGS and AGU conventions. Meet the next generation of Geoscientists from UH.
The Dr. Robert E. Sheriff Lecture Series:
Dr. Robert Sheriff has had a long and distinguished career in industry and academia. He was chief geophysicist at Chevron and a senior vice president at Seiscom Delta before coming to the University of Houston in 1981. He has authored, co-authored and edited several widely used books for exploration and production geoscientists, including: Applied Geophysics, Geophysical Methods, Reservoir Geophysics, Exploration Seismology, Problems in Exploration Seismology and their Solutions, Seismic Stratigraphy and his Encyclopedic Dictionary of Exploration Geophysics. He has played an instrumental role in helping build the reflection seismology faculty and staff in the Geosciences Department at UH to the largest in the nation. Dr. Sheriff contributes very generously in both time and funding to student and programmatic causes within both the Geoscience Department and the Allied Geophysical Lab.
He has recently contributed funding for two graduate student endowed fellowships at UH and has generously endowed the Robert and Margaret Sheriff Chair in Exploration Geophysics.
In recognition of Dr. Sheriff's many contributions to the University, the applied petroleum community and the geoscience profession as a whole, the University of Houston Geoscience Alumni Association initiated the Sheriff Lecture Series in 1999. We are very pleased that this year's lecture, which continues to honor Dr Sheriff as an educator, scholar, and a proponent for the geosciences, will be co-sponsored by the International Explorationists Group of the Houston Geological Society. The purpose of the Lecture Series is to attract top geoscience speakers with highly relevant ideas to exploration geology or geophysics. The lecture on "Africa's Vast Petroleum Reserves" by Dr. Kevin Burke will be the second in the series.