March, 2001
HGS Meetings

Joint HGS / GSH Dinner Meeting

"Interpretation and Modeling of Time-Lapse Seismic Data: Lena Field, Gulf of Mexico"

Abstract:

View Figures .

Two 3D seismic data sets from the Lena Field, Gulf of Mexico are analyzed for time-lapse effects. The seismic analysis involves cross equalization and residual migration of the post-stack seismic data, as well as full reprocessing and attribute analyses. The time-lapse differences for the B80 reservoir are compared with production data, geologic models, flow simulations, and forward seismic models. The time-lapse seismic difference anomaly is interpreted to be a region of gas invasion. Areas bypassed by the injected gas are identified from 4D seismic data as opportunities for infill drilling. Successful interpretation of this time-lapse seismic data illustrates the importance of integrating the results of modeling and simulation with seismic processing and interpretation.

Introduction

Seismic monitoring (time-lapse or 4D seismic) has the potential to significantly increase recovery in existing and new fields. One important issue is the significance of the seismic difference anomaly relative to non-repeatable noise. While future field developments should benefit from seismic acquisition designed for time-lapse monitoring, current seismic monitoring opportunities consist of existing fields for which one or more 3D seismic surveys have already been acquired. The reliability of a 4D interpretation is measured by the repeatability and the reconciliation of the time-lapse anomaly with geologic and production data. The objective of this paper is to interpret the seismic difference observed in the Lena B80 reservoir through the use of geologic modeling, flow simulation, and seismic modeling.

B80 Reservoir and Production History

The Lena Field (Mississippi Canyon Block 281) is located south of the modern Mississippi delta in 1,000 feet of water. The field is situated on the western flank of a salt diaper within a fault-bounded intraslope basin. The B80 reservoir is located about 10,500 feet below sea level and is interpreted as a low-stand fan systems tract representing deposition in distributary lobes composed of amalgamated and channelized turbidities. The average total porosity of the B80 sands is 27% and the permeability ranges from 30-200 md. The average reservoir thickness is 100 feet with a net-to-gross of 47%.

Oil production in the B80 reservoir began in 1984. The B80 has been depleted by a combination of bottom water and gas-cap expansion drive, supplemented with up-dip gas injection. Pressure decline below the bubble is believed to have trapped about 5% gas in the entire oil leg. In 1987 gas injection was initiated just below the original gas-oil contact. Gas quickly broke through to producers resulting from gravity. By 1995, most down-structure wells had watered out and many producers had high GOR production.

Seismic Data

A pre-production 3D seismic survey was acquired over the Lena Field in 1983 and a regional 3D spec survey covering the field was acquired in 1995, after 11 years of production. The 1983 survey was acquired in an east-west direction and the 1995 survey was shot in a N58oE direction. Initial differences in the two seismic data volumes are substantial and are primarily due to different acquisition and processing parameters.

A stepwise approach was taken regarding the processing of the two data volumes. Post stack re-processing represents an inexpensive, rapid analysis technique, while re-processing both data sets represents a more rigorous, expensive, and time-consuming methodology.

One of the obstacles to full reprocessing is that the navigation data for the 1983 data is unavailable. Navigation information was generated based on knowledge of the acquisition parameters, the final seismic grid, and observer's notes. The fidelity of the reprocessed volumes exceeds the original processing for both the 1983 and 1995 surveys, especially for steeply dipping reflectors at the salt flank.

For the relatively low dip B80 reservoir, which is removed from the salt dome flank, the time-lapse difference anomaly is similar for each processing stream.

4D Difference and Interpretation

Differences of the 1995 and 1983 surveys are calculated from interpolated time-aligned seismic traces and illustrated in Figure 1. There is a large difference anomaly unambiguously associated with the B80 reservoir. The anomaly is restricted to the reservoir (outlined by the polygon). The difference is nearly zero away from the reservoir, demonstrating that the data are repeatable and that the seismic difference is significant.

Reservoir flow simulation and the 3D geologic model are used to generate a synthetic seismic difference volume. Petrophysical analyses based on sonic and density logs relate the reservoir properties in the geologic and simulation models to seismic properties. A comparison of the synthetic and actual seismic differences is used to facilitate the interpretation of reservoir changes imaged by 4D seismic data.

Geologic Models and Simulation

Geologic models of effective porosity and shale volume are initially constructed independently for each parasequence using Sequential Gaussian simulation. Because the reservoir is below seismic resolvable thickness, collocated cokriging with Bayesian updating is used to incorporate seismic amplitude attribute information in the geologic model. The seismic attribute is corrected for the effect of reservoir fluids using forward seismic modeling. The resulting reservoir flow model has a good match between thte simulated and actual cumulative production history of the B80 reservoir

Petrophysics

Petrophysical analysis shows that from 1983 to 1995 the original water leg sees a very slight increase in impedance because the formation fluid pressure has declined, increasing the effective stress on the reservoir. Where oil has been swept by water, the impedance is almost unchanged because of the compensating effects of trapped gas, water displacing oil, and pressure decline on the rock frame. In the remaining oil leg, the small decrease impedance is again the result of trapped gas competing with the effect of pressure. Impedance in the original gas cap increases as a result of pressure decline. The gas-invaded zone, originally the up-dip portion of the oil leg, has the largest impedance change.

Seismic Models

Synthetic 3-D seismic volumes representative of the 1983 and 1995 reservoir conditions are derived from the geologic models, reservoir flow simulations, and the petrophysical analysis. The most significant change in the seismic response between 1983 and 1995 occurs in the gas cap expansion or gas injection zone. The seismic difference anomaly in Figure 1 is located in the area invaded by gas and represents regions of significant gas saturation changes.

Interpretation

As shown in Figure 3, the anomaly is restricted to the central portion of the reservoir, suggesting there may be regions of bypassed oil or areas not contacted by gas to the north and to the south. But, the area to the north may be an area of poor reservoir quality or an area swept by water as suggested by the flow simulation. Both conditions will result in little seismic change. Thus, an area of bypassed oil is identified to the south near the A29ST well. The interpretation is consistent with well production data.

Conclusions

Lena represents a significant challenge for the application of time-lapse seismic methodology. Even so, the time-lapse seismic analysis at Lena represents an important success. Post-stack processing and full reprocessing of the seismic data has shown that time-lapse differences in the B80 reservoir are distinct and robust. These differences are interpreted using reservoir simulation and forward seismic modeling to be the result of gas cap expansion and/or gas injection. By comparing measured time-lapse seismic differences with model predictions, areas bypassed by the injected gas can be identified. The identification of potentially bypassed oil may affect future drilling decisions.

Acknowledgment

We thank Exxon USA New Orleans Production Office for their support in this study.

Biographical Sketch:

David H. Johnston is a Research Associate for the ExxonMobil Upstream Research Company (URC) in Houston, Texas. He received a BS degree in Earth Sciences from the Massachusetts Institute of Technology in 1973 and a Ph.D. in Geophysics in 1978, also from MIT. He joined Exxon in 1979 and has held assignments in rock physics research, velocity analysis, and seismic reservoir characterization. He is currently technical team leader for time-lapse seismic research and is responsible for the development and the world-wide application of the technology.

Dr. Johnston is active within the Society of Exploration Geophysicists (SEG) and the Society of Petroleum Engineers (SPE). He was Secretary/Treasurer of the SEG in 1990, Chairman of the Development and Production Geophysics Committee from 1987 to 1988, and Chairman of the Interpretation Committee from 1991 to 1992. He has served on SEG, SPE, and OTC technical program committees and was Technical Program Chairman for the 1988 SEG/CPS Conference in Daqing, China.

In addition to a number of published papers in Geophysics and other technical journals, Dr. Johnston was co-editor of the book Reservoir Geophysics, published by the SEG in 1992 and co-editor of the SEG Reprint Series volume on Seismic Wave Attenuation published in 1981. He has presented numerous papers on rock physics and reservoir geophysics including keynote addresses at several conferences. Dr. Johnston was awarded the Best Presentation by the SEG in 1993, was an SPE Distinguished Lecturer from 1992 to 1993, and an SEG Distinguished Lecturer in 1999.

HGS Environmental / Engineering Dinner Meeting

" Offshore Environmental Issues for Oil and Gas "

Abstract:

Biographical Sketch:

HGS International Dinner Meeting

"Petroleum Geology of the Peng Lai 19-3 Oil Complex, Bohai Bay, Peoples Republic of China"

Poster Session

Abstract:

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The Peng Lai 19-3 (PL 19-3) Oil Complex, located in the south central Bohai Bay, People’s Republic of China, was discovered in May 1999 with the drilling of the PL 19-3-1 well by Phillips China Inc. The PL 19-3-1 intersected a gross 425 meter (1394 feet) hydrocarbon column in Miocene - Pliocene fluvial sandstones at a depth of approximately 1,000 meters (3280 feet). The PL 19-3-2 appraisal well, located 1.6 kilometers (1 mile) south-southwest of the discovery well, intersected a gross hydrocarbon column of 515 meters (1690 feet) in the same reservoir interval. Subsequent drilling of an additional five appraisal wells has proven that a large oil accumulation exists.

The oil complex is located on the northeast extension of a large basinal high and is interpreted as a north-south trending wrench anticline associated with a major north-south strike-slip fault system. En-echelon northeast-southwest trending normal faults are intersected by north-south trending wrench faults. Reservoirs are good quality, unconsolidated to semi-consolidated, stacked, post-rift fluvial sandstones within the Miocene Lower Minghauzhen and Guantao formations; with seals consisting of intraformational mudstones. Source rocks are organic-rich lacustrine mudstones in the syn-rift Oligocene Dongying / Eocene Shahejie formations located in the adjacent sub-basins. The oil quality varies from 13 - 23 degree API, with a broad range of viscosities, but with moderately low pour-points and low wax content. Gas-to-oil ratios are relatively low and range from 100 - 300 scf/stbo. A significant portion of the oil complex is masked by shallow gas covering approximately 30% (crestal portions) of the structure. A 4C, OBC seismic survey was initiated in the Spring of 2000 to help image this portion of the complex.

Phillips acquired the right to explore Bozhong Block 11/05 in 1994 when it signed petroleum contract with China National Offshore Oil Company (CNOOC). Phillips has a 100 percent undivided working interest in the 2.3 million-acre block. CNOOC has the right to acquire up to a 51 percent interest in any development in this block. The PL 19-3-1 discovery well was the fifth well Phillips China Inc. had drilled in Bohai Bay. Three of the previous wells were discoveries (BZ 22-2-1, Jan. 1997; PL 14-3-1, Nov. 1997; and BZ 36-2-1, Jan. 1998). Two additional discoveries were made in 2000 (PL 9-1-1 and PL 25-6-1). Phillips is evaluating the commercial viability of these five additional discoveries and has several other unexplored features that it plans to drill in the block.

  Biographical Sketch:

Michael D. Kuykendall received his B.S. and M.S. Geology degrees from Oklahoma State University and has over 19 years experience in domestic and international hydrocarbon exploration and exploitation. He previously was Senior Geologist with MASERA Corporation where he was involved in multiple geological exploration studies. In 1994 he formed Solid Rock Resources, Inc. which provided customized geologic consulting and integrated petra-stratigraphic technical services. He has author / co-authored several papers and presentations on various exploration and development aspects of clastic and carbonate reservoirs, and oil and gas fields. Since 1998 he has been employed as Senior Exploration Geologist with Phillips Petroleum Company, Worldwide Exploration Division, and is currently involved in exploration in Bohai Bay, offshore China. He is a member of AAPG, SPE, SEPM, and TGS.

Posters:

Poster #1:
"Investigation of a Neogene Petroleum System in the Ragay Gulf, GSEC 76: A Frontier Province in the Philippines"
by Linda Sternbach, Globex Energy and John Conolly, Petrofocus, Sydney, Australia

Poster #2:
"Gravity and Magnetics Interpretation of the Sunda Shelf and South China Sea"
by Dale Bird, Bird Geophysical and Dick Gibson, Gibson Consulting

Poster #3

"Gravity and Magnetics coverage over All of Mainland and Offshore China"
Mark E. Odegard, GETECH, Sugarland Texas.

NeoGeos Dimmer Meeting

"The Geologic/Geophysical Dialogue"

Abstract:

Most modern exploration is done by multidisciplinary teams, wherein each member brings his own expertise to the table, but must also be able to understand the other members' contributions. In particular, each must be able to understand the jargon, the assumptions, and the approximations of the other, in order to hold a constructive dialogue. A lot of cross-disciplinary education is important for all members of the team.

The geologist is typically the expert in synthesis; whereas the geophysicist is typically more expert in analysis. Because of this, the geophysicist is the more able to win an argument by appealing to the Laws of Physics, and to heavy computation; here are some questions to ask him, in order to (help) keep him honest:

Questions like these, along with the robust self-confidence needed to pose them, can go a long way toward helping the members of the team appreciate each other.

Biographical Sketch:

Dr. Leon Thomsen holds degrees in geophysics from Caltech (B.S. '64) and Columbia (Ph.D. '69). His academic career began with post-doctoral appointments at CNRS in Paris, and at Caltech, followed by faculty appointments at the State University of New York in Binghamton (1972-80). His industrial career began with 14 years at Amoco, at its famous Tulsa Research Center. Following the change of its mission in 1994, he joined Amoco's worldwide exploration department in Houston. Following the recent merger, he serves in BP Amoco's Upstream Technology Group in Houston, as Principal Geophysicist.

For his work in seismic anisotropy, Leon was given the Fessenden Award in 1994 by the SEG. He served as its Distinguished Lecturer in 1997, and as the Chair of its Research Committee in '99-'00. He and his colleagues received the EAGE's Best Paper Award in 1997 for their converted-wave analysis at Valhall, and several SEG "Best Paper Honorable Mentions". He was made an Honorary Member of the GSH in 1998.

HGS Emerging Technologies Dinner Meeting

"Knowledge Management & New IT Architecture Will Maximize Upstream Value-Creation"

Abstract:

Since long before the oil price collapse of 1998, the petroleum industry has been on a roller coaster ride that isn't over yet. Despite currently high oil prices, slowly rebounding energy stocks and a general atmosphere of optimism, our industry faces a number of serious challenges in the coming years.

For one thing, our workforce is rapidly aging and enrollments in petroleum-related university programs are at record lows. So we're facing an impending shortage of intellectual capital. That will impact our ability to make wise decisions. Knowledge management, therefore, must become a way of life, not just another buzzword.

What's more, energy companies are still not as consistently profitable as other investment alternatives in the marketplace. The oil and gas industry must leave no stone unturned in its quest for greater efficiency and productivity. New Internet-based IT architectures will be necessary to enable us to sustain and grow profitability not just at $25 or $30 per barrel, but at any oil price.

Part 1 of this talk will explore the "people problem" and issues of knowledge management in more detail. Part 2 will describe an emerging IT infrastructure that promises to lower costs and maximize both efficiency and value industry-wide.

Outline

Part 1: Knowledge Management

Part 2: Emerging IT Architecture

Biographical Sketch:

John Gibson became president and chief executive officer of Landmark Graphics Corporation in May 2000. Prior to that time, Mr. Gibson had been Landmark's chief operating officer since July 1999. He joined the company in 1994 and held various executive positions, including executive vice president of Landmark's Integrated Products groups, and president and vice president of Landmark's Zycor Division.

Mr. Gibson has played a key role in providing worldwide leadership to the company's development, marketing, sales and delivery groups. He has driven the development and delivery of innovations within specific scientific arenas, as well as the integration of those technologies to accelerate the activities of multidisciplinary teams from exploration to production, drilling and data management. John is credited with ensuring that continuous technical and process innovations would drive the commercial delivery of leading-edge technology and services based upon industry standards. He has been instrumental not only in Landmark's internal initiatives, but also in the identification and acquisition of essential technologies for rapidly deploying innovations and technology within the Landmark suite. John has provided executive leadership for many of Landmark's strategic relationships with technology partners including Halliburton, Western Atlas, Microsoft and Silicon Graphics.

His career in oil and gas began as an exploration geophysicist for Gulf Oil Company. Following the acquisition of Gulf by Chevron, Mr. Gibson became manager of geophysical and geological subsurface imaging for Chevron's Oil Field Research Company. He holds a bachelor's degree in geology from Auburn University and a master's degree in geology from University of Houston. He is a member of the American Association of Petroleum Geologists, the Society of Exploration Geophysicists and the Geological Society of America. He is also a member of the Board of Directors for POSC.

HGS Lunch Meeting

"Garden Banks 625 - A deepwater Gulf of Mexico post-drill review"

Abstract:

The Garden Banks 625 prospect was drilled in September 1998 to test several bright spot associated Pleistocene objectives in a salt withdrawal mini-basin. This post-drill review will briefly compare and contrast the results of this dry hole to a recently drilled 100+ MMBOE discovery near-by. This presentation was originally part of the HGS "Gulf of Mexico Dry Hole Seminar" held November 8, 2000.

Pre-drill technical analyses for this well included 3D seismic interpretation, AVO, instantaneous frequency, seafloor piston core geochemistry, and 3D acoustic impedance inversion calibrated to several wells within the basin. The integrated data suggested a strong likelihood of reservoir quality sands with a good chance for hydrocarbon saturation. AVO analysis indicated a strong class III response at both objective levels within the trap. A high GOR oil was predicted as the most likely hydrocarbon phase based on data collected from oil saturated seafloor piston cores. Top seal capacity and lateral stratigraphic pinch-out integrity were assessed to be the highest geologic risk attributes due to the shallow depth of burial below mud-line (5000-8000’), the apparent lack of reflector terminations and interval thinning at the limit of amplitude anomaly in the deepest objective level.

The well results confirmed the presence of high quality Pleistocene sand reservoirs as predicted. Post-drill log analysis, well-tie synthetic seismogram and mud log data showed that the sands had low gas saturation's of 10-20%. Well data confirmed the lack of adequate compaction to generate a top seal capable of trapping a commercial column of hydrocarbons. Seals that did form were subject to rupture due to frequent movement of allochthonous salt within the mini-basin. Several named tropical storms and hurricanes complicated drilling and logging operations and resulted in an incomplete wire-line log suite to evaluate the deepest objective. The well was plugged and abandoned on November 4, 1998.

Biographical Sketch:

Mark Sunwall is currently exploration manager for Texaco's Deepwater Gulf of Mexico Business Unit in Bellaire, Texas. He is responsible for prospect acquisition, maturation and rank wildcat drilling. Mark began his career as a geoscientist with Texaco, in 1976, after receiving a M.S. degree in geology from Miami University (Ohio). In the past ten years his work experience has included a broad range of technical and leadership positions in rank exploration, producing asset management and business development - both onshore and offshore Gulf Coast. He is a member of the New Orleans and Houston Geological Societies, AAPG, SEG and the Southeastern Geophysical Society.

Rob Alexander is currently a team leader for Texaco’s Deepwater Gulf of Mexico Exploration Business Unit. He is responsible for lease sale and farm-in evaluations, prospect maturation, coordinating geophysical efforts, rank wildcat drilling, and compilation of regional framework data. Rob began his career as a geoscientist with Texaco in 1992 after completing a Ph.D. in structural geology at the State University of New York at Albany, and a M.S. at the University of Alaska - Fairbanks. His experience includes research and exploration in the shelf and deepwater areas of the Gulf of Mexico, the coastal ranges and offshore basins of California, and the Brooks Range and North Slope of Alaska. Rob is a member of the American Association of Petroleum Geologists, the Geological Society of America, the American Geophysical Union, and the Houston Geological Society.