Preserving geology in reservoir modeling; a prectical application of stochastic modeling in heterogeneous reservoirs
Abstract:
Reservoir characterization is a difficult task particularly in the presence of limited well data. For example, modeling a field with good vertical resolution can present a problem if there are few wells, even in the presence of a 3D seismic survey. This, however, does not necessarily change the demand for immediate detailed information due to imposing deadlines for field development, limited time-windows of rig availability, seasonal constraints, or foreign government requirements. In the presence of such imposing deadlines, it is not uncommon to find the geologic model poorly constructed or even bypassed in lieu of a petrophysical model, the primary input to a reservoir simulator. Numerous pitfalls lie in a hasty approach, and resulting models are often found to be less than satisfactory and potentially the cause of a costly mistake.
The key to modeling such data is in the judicious use of geostatistics, blending both qualitative and quantitative information. For example, quantitative information from the well data can be used to supply vertical detail while seismic data and/or conceptual geologic models can supply information about horizontal continuity, geologic trends, or sequence stratigraphic constraints. The result is a detailed three-dimensional computer model that can be used for constructing reservoir fluid flow studies and a plan of development. While integrating the geologic detail into the model takes time, it is more efficient and less costly than running the model a second time, correctly. In this presentation, different methodologies are demonstrated from actual case histories.
Biographical Sketch:
Jeffrey M. Yarus was born in 1951 in Cleveland, Ohio. In 1969, he began his formal studies in Geology at the College of Wooster in Ohio. During his junior year, Yarus was awarded an opportunity to study geology at the University of Durham, England. Upon completion of this special program, he returned to Wooster and received his B.A. degree with honors in 1973. In September of that year, he Yarus began his graduate studies at Michigan State University under the supervision of Dr. Robert Ehrlich. At Michigan State, Yarus first developed his interest in computer mapping and numerical and statistical analysis.
Yarus followed Ehrlich to the University of South Carolina, where he finished his M.S. degree and continued through the Ph.D. program in geology. Yarus joined Amoco Production Company in New Orleans, Louisiana, in 1977 as a production geologist for the Gulf Coast Region. In 1980, he left Amoco and moved to Denver, Colorado, where he worked in the independent oil business for eight years. As an independent, Yarus worked a variety of domestic basins in the Rockies, mid-continent, and the Appalachian regions.
In 1988, Yarus was hired by Marathon Oil Company's Petroleum Technology Center as a Senior Mathematical Geologist. At Marathon, he played a major role in instituting the desktop computer mapping and geostatistical technology. He was responsible for providing training and consulting in this area for the entire company. Yarus left Marathon Oil Company in 1994 and joined GeoGraphix, Inc. as Manager of Customer Services. In 1996, he Joined GEOMATH, Inc. as the manager of Reservoir Characterization. Yarus has written a variety of papers and taught courses on computer mapping and applied statistical methods. His professional contributions are many, and include the AAPG edited volume entitled, Stochastic Modeling and Geostatistics; Principles, Methods, and Case Studies. Today, he works for Smedvig Technologies, Inc. in Houston, Texas where he is the Manager of Advanced Reservoir Characterization, support and services.
"TITLE RESEARCH: Unraveling the Environmental Record"
Abstract:
Title research is the examination of public records to disclose facts regarding the ownership of real estate. The title, or evidence of ownership, is recorded for public record at the county courthouse. Determining a property's title history requires an examination of all documents filed for public record on the subject property. This includes the records of the Appraisal District, County Clerk, County Tax Assessor, and can include a review of deeds, mortgages, wills, litigation, and property taxes. The challenge is the ability to find these documents and construct a chain-of-title when provided only a minimum of information and working with a public record system that can be vague and inconsistent.
Fight the post-holiday blues and come have dinner with us as we dress as Sherlock Holmes and explore the dark, musty basements of public civil service (Flashlight not needed).
Biographical Sketch:
Ms. Gorman founded BAST Research Services, Inc. in 1994 and has worked in the title industry for twelve years specializing in researching titles for real estate transactions.
At the conclusion of the lecture, all interested people are invited to attend a meeting to outline the design of a compendium of geology for the City of Houston. This is an important project that will need volunteers to research and write on various topics such as depostional history, structure, stratigraphy, and geomorphology as they apply to the area we live in work in.
The Western End of the Jebilet High Atlas System, the Onshore and Offshore Essaouira Basin (Morocco), and the Virtually Unexplored Cap Tafelnay Folded Belt
Abstract:
Note: The figures from the Bulletin article did not reproduce well here on this web page. Please refer to the January, 1999 issue of the Bulletin to view the figures.
Introduction
East of Marrakech, the High Atlas of Morocco splits into a northern Jebilet and a western High Atlas branch. The onshore Essaouira basin is between these two branches (Fig. 1). Gas and condensate production is from structures involving Triassic-lower Liassic siliciclastics in the Meskala and Zelten fields and from fractured Jurassic carbonates in the Toukimt, Jeer, N'dark, and Kechoula fields. The same fractured carbonates produce oil in the Sidi Rhalem field. Anhydrites form the seal of these petroleum traps. Broughton and Trepanier (1993) established the presence of Carboniferous and Oxfordian petroleum source beds onshore.
Offshore, the Atlas system intersects the Atlantic passive margin of Morocco. A Mesozoic carbonate shelf margin paral- lels the coast, but locally changes into an E-W direction at the latitude of Essaouira (Fig. 1). The right-angle intersection of a folded belt with a coeval passive margin is unusual and raises many questions concerning the influence of facies and older structures on structural styles of deformation. This summary is based on the Ph.D. dissertation (in progress) of M. Hafid, which includes the review of more than 4500 km of seismic profiles.
Onshore Stratigraphy and Structure
Onshore and under the nearshore continental shelf, the basement consists of an eroded Paleozoic folded belt. Superimposed on this basement peneplain and mimicking its structural grain are NNE-SSW striking half grabens that formed in the Late Triassic to early Liassic. Transfer faults, striking roughly E-W, link these half grabens. A wide, less faulted, evaporitic sag basin and extensive basalt flows overlie them. A pre-Pliensbachian "breakup" unconformity truncates the Triassic to lower Liassic sequences on the E and WNW margins of the basin. A mid Liassic to Lower Cretaceous platform sequence overlies the unconformity. In the Cap Sim-Necnafa depression, Jurassic and Early Cretaceous salt tectonics caused widespread salt withdrawal structures. Tertiary NNW to SSE compression caused the inversion of the Late Triassic and early Liassic extensional system and/or the formation of salt anticlines. The same compression is responsible for E-W striking Tertiary faults that reactivated the older transfer faults.
Offshore Stratigraphy and Structure
The near-coast shelf is underlain by an uplifted shallow Jurassic to Lower Cretaceous shelf margin characterized by pronounced Tertiary shelf margin flexure (SMF on Section 8a in Fig. 2). Below the outer shelf and continental slope, deep basement dips rapidly westward from roughly three km to depths greater than eight km. This deep basement probably represents an oceanic/transitional crust that formed in the Early to Middle Jurassic. Beyond and to the west of the carbonate shelf margin, all Mesozoic sediments are likely to be a pelagic facies.
The Cap Tafelnay folded belt (Section 8b in Fig. 2) represents the deep-water continuation of the onshore Essaouira basin and the structural termination of the western Atlas. As shown on Fig. 2, this folded belt involves an evaporite-based decollement and a dramatically southward-thickening Mesozoic basinal sequence. The Cretaceous portion of this sequence was deposited in a flexural basin that responded to tectonic loading by the nascent Atlas Mountains to the south. Angular unconformities show that the deformation in the folded belt began in the mid-Cretaceous and continued into the Tertiary.
Cap Tafelnay folds striking NE-SW formed over a poorly defined d6collement that "ramps" down into the underlying Paleozoic continental basement toward the east. This northerly striking lateral ramp system, more than 80 km wide, coincides with the pronounced Late Cretaceous-Tertiary shelf margin flexure (SMF). Toward the NE, the lateral ramp appears to merge with the main fault associated with the J. Hadid J. Kourati inversion structures and from there connects with the E. Jebilet reverse fault on the frontal ramp.
Conclusion
The deepwater Cap Tafelnay folded belt is virtually unexplored. The Cap Sim well (Fig. 2) penetrated the Cretaceous without encountering significant reservoirs and bottomed in Triassic to lower Liassic diapiric evaporates. Albian-age basinal clays from DSDP Site 545 (approximately 200 km farther north) are reported to have a high organic carbon content (Deroo et al. 1984; Rullk6tter et al. 1984). Steiner et al. (1998) report minor Oxfordian black shale intervals from a basinal section outcrop in Fuerteventura. Thus, together with the Oxfordian source beds reported by Broughton and Trepanier (1993), we cannot preclude the presence of a regional Oxfordian source. So far, most offshore exploration has targeted shallow-water carbonates. The basinal section remains virtually unexplored. Assuming adequate economic incentives, the fold belt remains an intriguing deepwater exploration target for the ftiture.
References
Broughton, P. and A. Trepanier, 1993, Hydrocarbon generation in the Essaouira basin of western Morocco. AAPG Bulletin 77:999-1015.
Deroo, G., J. P. Herbin, and J. Roucache, 1984, Organic geochemistry of Cenozoic and Mesozoic sediments from deep sea drilling sites 544-547, Leg 79, Eastern North Atlantic. In: Hinz K., E. L. Winterer, et al., Initial Reports of the Deep Sea Drilling Project (DSDP), vol. 79: Washington (U.S. Govmt. Printing Office).
Rullkotter, J., P. K. Mukhopadhyay, R. G. Schaefer, and D.H. Welte, 1984, Geochemistry and petrography of organic matter in sediments from the Deep-Sea Drilling Project Sites 545 and 547, Mazagan Escarpment. In: Hint. K., E. L.Winterer, et al., Initial Rpts. DSDP, vol. 79: Washington (U.S Govmt. Printing Office).
Steiner, C., A. Hobson, P. Favre, G. M. Strampfli, and J. Hernandez, 1998, Mesozoic sequence of Fuerteventura (Canary Islands): Witness of Early Jurassic sea-floor spreading in the central Atlantic. GSA Bull. 110(10): 1304-1317.
Biographical Sketches
Mohamad Hafid is an assistant professor at the University Ibn Tofail, Kenitra, Morocco. In 1981 he received a B.S. from the University Mohamed V in Rabat. For six years he worked as a petroleum geologist for ONAREP, the national oil company of Morocco. During that time he also obtained an M.S. degree from the University of South Carolina in 1986 with a thesis on the Guercif basin, Morocco. From 1990 to 1992, he was an assistant professor at the Univ. liassan II in Casablanca and in 1993 he joined the staff at the Univ. Ibn Tofail. He is working on his Ph.D. degree at the University of Rabat, Morocco. In 1994, 1996, and 1997, Mohamad was a visiting scholar at the Geology and Geophysics Department of Rice University. He anticipates defending his dissertation in 1999.
Albert W. Bally obtained a Ph.D. degree from the University of Zurich, Switzerland in 1952. His dissertation project was in the central Apennines of Italy. After a year of postdoctoral work at the Lamont-Doherty Fartli Observatory of Columbia University, he joined Shell Canada in Calgary. In 1966 he was transferred to Houston to become manager of geological research at Shell Development Company. He advanced to become chief geologist and senior exploration consultant for Shell Oil. From 1981 to 1996, A. W. Bally was the Harry Carothers Wiess Professor of Geology at Rice University. He retired and is now Professor Emeritus at Rice.
"Large Scale & Fast Volume Visualization"
Abstract:
Michael J. Zeitlin will discuss advances in large scale volume
visualization. In a time of low oil prices, finding reserves more quickly
with less risk is a must in order to continue operating profitably.
Advanced technologies which reduce uncertainty are needed more than ever.
The presentation will focus on visualization technology as an enabling tool
to improve margin in a low price environment. Critical to success is the
ability to examine very large data sets interactively and reveal hidden but
important features within 3-D seismic data. The presentation will highlight
projects completed using Texaco's Visualization Center which has helped cut
cycle time in seismic analysis from the typical 3 weeks to 3 days on
average; identified new prospective zones not previously identified and
discovered new reserves.
Biographical Sketch:
Michael J. Zeitlin is Portfolio Manager of Texaco's Integrated Reservoir Information and Global Visualization Technology. He has held previous leadership positions with Texaco since 1980 including basin modeling, computer aided exploration and hydrogeology. During the past 6 years, Mr. Zeitlin has been the driving force in Texaco's effort to acquire, develop and deploy 3D visualization technology throughout TexacoÆs business units including the first commercial installation of the industries first visualization center. He has received several top honors from Texaco including Texaco's General Manager's Outstanding Contributors award (1993 & 1995), bottom-line impact (1993) and new product development (1993) awards. He has also been selected to receive the Carnegie Mellon Universities and American Management Institute award for management excellence in Information Technology (1998).
Before joining Texaco, Mr. Zeitlin received a BSc. double degree in Earth and Space Science and Biology from the State University of New York at StonyBrook, Long Island. He also received a Msc. degree in Geological Oceanography from the Marine Science Research Institute at StonyBrook. He is an active member of the American Association of Petroleum Geologists, and the Institute of Electrical Engineers Computer Society.
Compartmentation of Oil and Gas Fields: A Geochemical View
Abstract:
Gas and oil fingerprinting techniques allow the prediction of compartments in a detailed manner as it is not possible with 3D seismic analyses. scale.
Natural gases and oils vary in their chemical and isotope composition as a function of their formation and migration history. Compositional and isotopic variations are often caused by mixing of two or more compositionally and isotopically different gases. Isotopic properties in gases can be used to determine the mixing ratio of the two end members and/or calculate the composition of the end members from different mixing ratios. The variation of isotopic properties of gases within a continuous reservoir are generally small but can be significant between fault blocks of one reservoir or between unconnected but closely stacked reservoirs. These inter-reservoir variations can be utilized to help solve many of the problems occurring during gas field development and operation.
Fingerprinting Of Oils and Gases:
Isotope analyses of C1 to C4 compounds in natural gases a precise correlation of gases through a comparison of their compound isotope patterns (isotopic fingerprints).
Reservoir Identification:
Oils and gases in reservoirs of most oil and gas fields exhibit differences between individual reservoirs due to different filling and mixing histories. In many oil and gas fields, each reservoir can be differentiated from another but gases within a single reservoir are very similar. Isotope analyses of gases could be helpful in such cases to identify the production zone in new completions.
Reservoir Compartmentalization And Fault Block Mapping:
Numerous case histories show subtle compositional changes across sealing faults. Thus oil and gas analyses can be used to indicate compartmentation into fault blocks. Such variations can be used by field geologist to better define faults and reservoir configurations. We will show results of a new GRI study that shows that gas isotope analyses readily identify production compartments.
Production Allocation.:
Isotope analyses in commingled production could be used to allocate contributions from individual sands if isotopic differences exist between the gases from the contributing reservoirs. Theoretical mixing curves for two end member scenarios and three end member scenarios will be discussed.
Production Monitoring Of Conventional And Horizontal Wells.:
Production monitoring is a new application of gas isotope analyses which could be particularly valuable for horizontal wells. Isotope variations in the produced gases would reflect variations in the input of different reservoirs. Chevron has developed computer programs which allow to determine the individual contribution of up to 5 different reservoirs from the analysis of the commingled production.
Biographical Sketch:
Martin Schoell received his Ph.D. at University of Clausthal/Germany in 1970 and obtained a lecturer degree (Habilitation) in 1983 at the University of Bochum in Germany. Martin worked for 13 years at the German Geological Survey on isotope geochemistry of hydrothermal systems and natural gases. He joined Chevron Petroleum Technology Company in 1984 and conducts research and regional studies in petroleum and natural gas geochemistry. He lectures extensively in Chevron on natural gas geochemistry and works with affiliate offices on large regional studies on petroleum formation and occurrence in SE Asia and NW Australia. He is editor of many special publications on Natural Gas and Isotope Geochemistry and has published more than 70 papers on Natural gas, petroleum- and bio-geochemistry. Martin won the AAPG best paper award in 1995 and was AAPG distinguished lecturer 1996/97.
Methodology for Minibasin Ranking in the Deepwater Gulf of Mexico
Introduction to abstract
This paper was presented at the September 1998 AAPG Hedberg Research Conference, Integration of Geologic Models for Understanding Risk in the Gulf of Mexico. The paper is a synopsis of part of the work resulting from an alliance between Mobil Deepwater Business Unit and Phillips Petroleum North American Exploration Group. The alliance Regional Study Group was charged with developing a regional framework and risk scenarios in which to evaluate prospects in the deepwater Gulf of Mexico. One of these methods was the delineation and classification of minibasins based upon internal stratal geometry, salt withdrawal styles, accessibility to hydrocarbon charge, and internal hydrocarbon migration focus. The minibasin classification scenario presented incorporates prior published research on salt tectonics and depositional systems focused towards regional risk assessment.
Abstract:
Deepwater northern Gulf of Mexico is characterized by extensive allochthonous salt
sheets with isolated minibasins. Assessing the exploration potential of these minibasins
requires an integration of all the petroleum systems elements. An analysis of minibasins
in the Garden Banks, Green Canyon, Keathley Canyon and Walker Ridge protraction areas
shows the relationship of stratal and structural architecture to
the interaction of sedimentation and salt movement. Minibasins are broadly
classified using stratal and allochthonous salt geometries into
five basin types (Fig. 1).:
Ramp basins predominate on the slope in Garden Banks and Green Canyon. They are characterized by a south-bounding, north-dipping salt ramp. Most ramp basins have young thick depocenters adjacent to the counter regional ramp. Ramp basins tend to be asymmetric and larger in areal extent. Welded basins were previously underlain by allochthonous salt that has been fully or partially evacuated. They increase in frequency southward into the Walker Ridge and Keathley Canyon protraction areas.
Welded listric (Roho) basins have south-dipping arcuate faults that sole into the evacuating salt. Welded basins have a multitude of patterns of internal faulting and sediment fill, some are symmetrical with bowl-shaped fill, others have multiple depositional axes and bi-directional stratal fill.
Primary basins show no evidence of allochthonous salt and display continuous sedimentary fill from Cretaceous to Recent. Salt-floored basins are underlain by continuous allochthonous salt which shields them from the underlying petroleum kitchens.
Salt-floored basins occur along the down dip edge of allochthonous salt near the Sigsbee escarpment and above very young salt sheets in Garden Banks and Green Canyon.
As basin fill changes through geologic time, each of the basins has differing capability to receive and internally distribute the hydrocarbons it receives via a complex plumbing system from sources at greater depths below the basin. Regional classification of the basin types combined with mapping the sequence stratigraphy framework within the basins provides a spatial and time framework for evaluating risk more effectively. In general, hydrocarbon entry points to basin strata are controlled through time by salt movement and geometry.
Using this basin ranking methodology, ramp basins have attractive plumbing and enhanced trapping focus. Welded and welded listric basins are dependent on the evacuation of the salt floor for charge to occur, therefore the age and areal extent of the weld are factors. Primary basins appear to have access to underlying sources but may lack effective migration pathways and trapping geometries. Salt-floored basins are the lowest ranked basins due to separation from source. Within the four protraction areas, most discoveries have been in ramp and welded minibasins (about 1BBOE in each basin type). Primary, salt floored, and unclassified basins have minor discoveries, none of significant size.
Biographical Sketch:
Al Koch is the Petroleum System Advisor for the Mobil Deep Water Business Unit in New Orleans. He has worked for the past six years in the deepwater Gulf of Mexico evaluating the regional elements of the petroleum system and developing means of risk assessment. His career with Mobil has spanned 28 years working in both research and exploration in multiple basins worldwide emphasizing the application of petroleum systems technology. He receives a Ph.D. in geology from the University of Washington, Seattle in 1970.
Vinod Mathur is currently a Senior Geophysical Advisor with Mobil E&P U.S. He is involved with regional analysis of the deepwater depositional systems and play concepts and is the Coordinator of all regional deepwater Gulf of Mexico sequence stratigraphy projects. He holds an MS in Geophysics from the Centre of Exploration Geophysics, Osmania University, and attended Technical University, West Berlin in Graduate Studies.
Rick Nagy is a Senior Exploration Geologist in Phillips Petroleum Company Deepwater Exploration Team in Houston. He has 18 years of industry experience and joined Phillips in 1989 working in their Regional Studies Group. Project areas included primarily the Gulf Coast, but prior experience ranged from offshore California to Alaska. He also worked in the Phillips Subsalt Exploration Team prior to 1996. Has a degree in Geology from San Diego State University and is a current member of AAPG (C P G #5364), HGS, and SPWLA.
Frank C. Snyder is currently the team leader of the Alaska Exploration Team, Phillips Petroleum Co., Houston. Prior to May of 1998 he was the Principal Geologist in charge of Regional Studies in the Deepwater Exploration Team. In this group he was responsible for regional geological synthesis, play generation, and prospect evaluation in the deepwater, offshore Louisiana. Over the past seventeen years he has worked a variety of geological basins in the North Sea, Norwegian Sea, Rocky Mountains, Australia, China, and Gulf of Mexico subsalt trend as an exploration and development geologist. He received his formal education at Louisiana State University, Baton Rouge, graduating with an MS in Geology in 1981.