September, 1999
HGS Meetings

Environmental / Engineering Dinner Meeting

Introduction to DRIS—Deep Remediation Injection System

Abstract:

The Deep Remediation Injection System (DRIS) is a method utilizing the in-situ placement of remedial agents and air for on-site subsurface cleanup operations. It injects agents such as oxidizing chemicals, microbes, and nutrients into contaminated soils and groundwater to depths of 30 feet. High-pressure, low-volume injection is done with portable equipment. Air simultaneously injected through a lance into the impacted media increases the effectiveness of the remediation method.

Biographical Sketch:

Mr. Horsak received a B.S. in engineering from the University of Texas at Austin and an M.S. in environmental science from U.T. at San Antonio. He has worked 26 years in all phases of environmental management. Mr. Horsak has worked on many of environmental projects with companies such as Brown & Root, Beck and Associates, NUS, Roy F. Weston, M.W. Kellogg, McLaren Hart, and most recently as the owner of Petra Environmental. He is the author of many papers on topics such as remediation and cost control, pollution prevention, regulatory trends, hazardous waste disposal, geothermal energy, and environmental auditing. Randy's project experience includes regulatory audits, remediation, training seminars, risk assessments, air permitting, engineering feasibility studies, and hazardous waste disposal for sites in the United States and Mexico.

HGS Dinner Meeting

"Subsalt Exploration in the Deepwater Foldbelts of the Gulf of Mexico: Regional Analysis of a Giant Petroleum System"

Abstract:

The geologic setting of the distal U.S. waters is characterized by a complex assemblage of salt-related compressional features. In the U.S. western Gulf, the Perdido Foldbelt is a north—south trending zone of shortened Mesozoic through Miocene strata covering an area of over 30,000 square kilometers. In the deep east central U.S. Gulf, the Mississippi Fan Foldbelt is an arcuate trend of folded/thrusted Mesozoic through Pliocene strata encompassing over 25,000 square kilometers. Approximately 80% of each trend is in the subsalt environment. The difficult seismic imaging of these subsalt trends necessitates a regional approach to understand the development and prospect potential in these vast areas.

Our regional methodology employs source rock analyses, potential field and basement mapping, regional structural mapping of key horizons including the top and base of salt, regional cross- sections, stratigraphic studies and depth-migrated seismic imaging. Basement-controlled thickness and distribution of the Louann Salt and subsequent sediment loading history are the primary controls on the location, distribution, and character of the foldbelts. These primary controls are responsible for observed changes along the regional strike and dip of the trends that include structural inversion. Compression in both areas has lifted objective intervals up to 4 km above regional elevation. Folding accommodates only a small portion of the total regional extension, with the emplacement of the Sigsbee salt canopy serving as the primary balancing mechanism. Understanding the linkage between contraction of the objective intervals and the emplacement of the overlying salt canopy is the key to successful exploration in these trends. Because emplacement of the canopy is partially synchronous with folding, a correlation exists between the structural grain of the subsalt folds and the base of allocthonous salt.

Primary reservoir objectives in both foldbelt trends are Tertiary-age turbidites, although a higher-risk poorly understood Mesozoic section is present. Hydrocarbon sources for both trends are from Upper Jurassic and Lower Cretaceous marls, with the Perdido Foldbelt also accessing potentially mature Paleogene intervals. The combination of large structural traps, rich source rocks, potentially excellent reservoirs, and a regional top seal places the subsalt foldbelts in the forefront of future Gulf of Mexico exploration.

Biographical Sketch:

Mike Roberts received a Bachelor's degree in geology from Bowling Green State University (Ohio) in 1982 and his Master's degree in geology from the University of Cincinnati in 1984. He has been employed by Chevron since 1984 and has spent these 15 years working in Chevron's New Orleans office. Mike has had numerous assignments across the GOM and has spent the last 11 years working in deepwater exploration. Mike is a member of NOGS, AAPG, and SEPM. Mike's professional interests are in salt tectonics, basin analysis and regional studies.

Poster Session

Regional Depositional Systems of the Vicksburg Formation, by Janet M. Combes, Ph.D.

The lower Oligocene Vicksburg Formation of the Texas Gulf Coastal Plain contains major petroleum reservoirs in the Rio Grande Embayment and the Houston Embayment. Several discoveries in these areas over the past few years have led to renewed interest in the potential for undiscovered fields in the embayments as well as in the San Marcos Arch region. Knowledge of the depositional systems distribution during Vicksburg times is essential to understanding sand concentration and is fundamental to effective exploration and production of the section.

International Dinner Meeting

Chronostratigraphy, Sedimentary Facies, and Architecture of Tectono-Stratigraphic Sequences within a Miocene Rift, Gulf of Suez, Egypt

Abstract:

The Miocene synrift stratigraphy of the Suez Rift records the complex interplay between the structural development of the rift and the sedimentary response to tectonics. Along the Sinai margin of the Gulf of Suez (GOS), the Miocene sediments were deposited during the three main phases of rifting: rift initiation, clysmic rifting, and early post-rift. In general, this stratigraphy records the progressive subsidence and drowning of the basin during rift initiation and the clysmic stage, followed by isostatic adjustment and shallowing during the early post-rift stage.

A regional synthesis of the Miocene stratigraphic sections exposed along the Sinai margin of the Gulf of Suez has resulted in a depositional and sequence stratigraphic model for these strata that integrates tectonic history and sedimentary response during the early, clysmic, and post-rift phases of basin evolution. The development of this model was made possible by establishing rigorous chronostratigraphic control based upon micropaleontology and magneto-stratigraphy. Application of this model, along with 3-D seismic, has had a major impact on the ability to recognize stratigraphic and subtle combination traps within this mature basin, resulting in a 75% increase in exploration drilling success (1993–1997) and an increase in production of 164,000 BOPD (IP).

Graphic correlation of paleontological data from wells and outcrops reveals that the Neogene section consists of at least eight biostratigraphic sequences (S10–S80) separated by graphic terraces (T00–T70) or geologic hiatuses (gaps in time). Outcrop analysis of terraces T00 to T30 and their associated fossil assemblages indicates that they represent either regional regressive or transgressive events. The number of depositional sequences (those bounded by regressive erosional surfaces) is therefore less than the number of paleontologically defined sequences. Terraces T00 and T20 are sequence boundaries, and subsurface evidence suggests that T40 is a condensed interval and that T50 is an erosional unconformity (sequence boundary). Field observations of T10 at Wadi Thal in the Sinai indicate that it consists of at least two ravinements and a condensed section within a narrow stratigraphic interval. Similarly, the T30 hiatus associated with the Markha Anhydrite at Wadi Feiran is composed of several stacked flooding and regressive surfaces. These surfaces at both Wadi Thal and Wadi Feiran represent minor time breaks. These small lacunae cannot be individually resolved by graphic correlation, but their sum total within a thin rock (hiatal) interval is detectable as a graphic correlation terrace. Despite limitations in resolution, graphic correlation of paleontological data was crucial for recognizing key surfaces and intervals that allowed us to decipher the sequence stratigraphy of the Miocene synrift section of the Gulf of Suez and to make more precise correlations within the basin.

The key stratal surfaces and intercalated sequences can then be related to the tectonic evolution of the GOS. T00, for example, represents the pre-rift unconformity. The initiation phase of the Suez Rift is recorded by deposition of the Aquitanian Nukhul Formation (S10). Rift initiation was characterized by northerly flowing fluvial systems that occupied the downthrown segments of asymmetric half-grabens. Increased subsidence resulted in a relative sea-level rise that flooded the half-grabens and created elongate estuaries and, ultimately, shallow marine environments. Nukhul depositional facies include: continental alluvial valley fill, estuarine, tidal flat, tidal channel complexes, and shallow offshore marine. The clysmic phase began with uplift of the rift shoulders and concomitant basin subsidence. This resulted in a period of progressive sediment starvation within the basin (T10) as sediment sources adapted to the new topography. The clysmic stage of rifting is recorded by deposition of relatively deep marine mudstones, basin-floor fan sandstones, and footwall-margin conglomeratic-talus cone and fan delta deposits of the Mheiherrat Formation (S20). Continued extension and crustal thinning resulted in isostatic uplift, shallowing of detachment depths, and increased rotation of fault blocks (T20). The later stages of the clysmic rift were documented in the channelized submarine fan, offshore marine, deltaic, lacustrine, and hypersaline lagoon/sabkha deposits of the Hawara, Asl, and Ayn Musa formations (lower S30). The early post-rift phase is recorded by open marine mudstones and delta front deposits of the Lagia and Ras Budran members of the Ayun Musa Formation (upper S30 and S40).

Within the subsurface of the Gulf of Suez, seismic data are generally poor because of energy attenuation by shallow evaporites, multiple reflections, and complex structure. These conditions make traditional seismic sequence stratigraphy techniques difficult to apply. However, the tectono-sequence stratigraphic model developed from outcrops and the paleontologically-defined chronostratigraphic framework provides tools that allow for better subsurface correlations by systematically mapping stratal geometries using sequence boundaries and flooding surfaces defined by high-resolution biostratigraphic data. The stratigraphic picture that emerges from application of these concepts creates a profound change in quantification of fault throws and recognition of stratigraphic and combination traps. In addition to revealing new plays, application of the tectono-stratigraphic model also results in a better understanding of reservoir geometry and distribution. Biographical Sketch:

William (Bill) Krebs received his B.S. (geology) from UCLA in 1970. He did dissertation research in Antarctica and in 1977 received his Ph.D. (geology) from UC Davis. He joined Amoco Production Co. in Denver in 1978 as a biostratigrapher for west coast and Great Basin exploration. In 1987, Bill was transferred by Amoco to Houston where he worked as a chrono-stratigrapher and paleontological coordinator for international exploration. He has had project experience in numerous foreign countries, and in recent years has worked extensively in Egypt and Turkey. Bill retired from BP Amoco in 1999 and now consults. He has published 27 articles on paleontology and stratigraphy.

Bill Wescott received his undergraduate degree in geology from Franklin and Marshall College in Lancaster, Pennsyl-vania. After serving in the U. S. Army, he continued his geological education, earning an M.S. degree from Southern Illinois University at Carbondale and a Ph.D. from Colorado State University. From 1979 until 1984 he worked a series of domestic exploration projects for Amoco Production Company. In 1984 he transferred to Amoco's international new ventures group and spent the next 15 years engaged in a variety of world-wide exploration activities, predominantly in Africa and the Middle East. He is presently a consulting geologist specializing in sedimentology and sequence stratigraphy.

Bill Wescott has authored or co-authored more than 75 papers, abstracts, book chapters, and field guides. His present research interests are the evolution of depositional systems and development of stratigraphic sequences in extensional settings and imaging paleo-depositional systems using 3-D seismic.
Bill Wescott can be contacted by e-mail at atwwescott@flash.net

Emerging Technologies Dinner Meeting

Breaking the Rules for Seismic Reservoir Analysis

Abstract:

Criteria for the selection of reservoirs suitable for monitoring have been developed based on either theoretical principles or discussions around the water cooler.

In general, it is concluded that the optimum case for advanced characterization and monitoring is for low-dip, low-velocity strata that have a low-modulus fluid moving during the production process coupled with a high signal-to-noise ratio on the seismic data. Given these assumptions there is a strong tendency for the selection of reservoirs suitable for monitoring and advanced seismic characterization to be clastics associated with high GOR oils, or with gas movement on marine seismic data.

A more aggressive strategy using multi-component acquisition, alone or in combination with permanent installations, offers the opportunity to break these rules and develop methods for reservoir description extending across a wide range of traps in more challenging signal-to-noise provinces. To accomplish this goal, advancements are required in several areas:

Results from field experiments demonstrate that there are significant developments suggesting that future surveys will capitalize on improved coupling, multi-component analysis, and new algorithms. Combining multi-component recording with new acquisition and processing concepts provides the opportunity to improve both the characterization and monitoring of reservoirs that are outside conventional wisdom for seismic work. New results extend the concept of reservoir work to include fracture mapping, detection of sand/shale ratios, and monitoring of non-gas fluid movement.

Biographical Sketch:

John (Jack) Ward started his career in development geology with Texaco in 1974. In 1978 he began working with Teknica in Houston, developing quantitative techniques for seismic mapping of stratigraphic traps using seismic sonic logs. In 1991 he co-founded Simon Geolithic and engaged in AVO analysis, adding these observations to the characterization of reservoir properties. Current work at PGS includes integration of multi-component methods and permanent installations for advanced reservoir characterization and monitoring. Dr. Ward received his degree in geology from SUNY Binghamton in 1978.

HGS Lunch Meeting

"Subsalt Turtle Play, Walker Ridge Area, Deepwater Gulf of Mexico"

Abstract:

The Miocene section under the Sigsbee Escarpment salt in Walker Ridge offers several plays with large reserve potential. Plays include the western edge of the Mississippi Canyon fold-belt trend extending under the salt, large salt pillows showing minor compressional effects, and finally turtle structures that exist upslope and landward from the folds and pillow structures.

Turtle structures formed in Miocene sediments as a result of autochthonous Jurassic salt withdrawal. Broad elliptical low areas formed during Late Cretaceous and Paleogene time, flanked by low-relief salt pillows and ridges. Sand-prone Early—Middle Miocene turbidite sediments ponded between the salt highs, accentuating the height of the salt ridges. Collapse of the flanks of the salt ridges during late Miocene time flexed the edges of the Miocene depocenters creating turtle features. Large volumes of salt escaped through near-vertical feeders above the salt ridges forming an extensive, thick, salt canopy system above the Miocene section. Many of the vertical salt feeders formed above basement fault trends, indicating an inter-relationship of the rift geometry and later salt mobilization. During Pliocene—Pleistocene time, large suprasalt mini-basins developed above the salt canopy, substantially modifying the allochthonous salt distribution and masking much of the subsalt geometry.

Drilling these structures will be challenging. Water depths range from 6,000 to 7,500 feet. Salt sheet thickness varies from 7,500 to over 20,000 feet. Drilling depths of up to 30,000 feet are necessary to reach the prospective intervals. However, reserve potential is high ranging form 200 to 900 MBOE per structure.

Biographical Sketch:

Rick Nagy is a senior geologist with Phillips Petroleum Company currently assigned to its Deepwater Exploration Group as regional mapping team leader. He has over 19 years of exploration experience in many domestic basins including onshore and offshore Alaska, offshore California, and the entire Gulf of Mexico region. Prior assignments were in the Regional Studies Group with projects in many areas of the Gulf both onshore and offshore, and then in the Sub-Salt Exploration Group. His recent experience has been in the Gulf of Mexico deepwater trend, where responsibilities include regional geological synthesis of deepwater depositional systems and salt tectonics, play generation, and prospect evaluation. He has a B. S. degree in geology from San Diego State University.

SPE Lunch Meeting

SPE Reservoir SG: 3D Seismic in a Cost-Constrained E&P Environment

Abstract:

Delivering high performance by eliminating dry holes and marginal wells and by finding previously undefined locations and prospects, 3D seismic has had a profound impact on the E&P industry in the last decade. Three-dimensional seismic reduces exploration finding costs and increases reserves on major properties. But, as the industry finds itself in a low-product-price environment that may have been caused, to some degree, by 3D-guided E&P success, close examination of the technology is in order. Through data and examples, the lecture explores the accomplishments and limitations of 3D seismic.

Biographical Sketch:

William (Bill) K. Aylor, SPE, recently retired as a geophysicist with BP Amoco and is currently engaged part time in geophysical consulting, specializing in 3-D seismic strategic planning and technology valuation. He is a 1999 SPE Distinguished Lecturer. Mr. Aylor holds a BS degree in Physics from the University of Texas at El Paso.