Half-Day Thrust Tectonics Symposium
The meeting cost is $35, which includes a catered lunch, posters and demonstrations during the afternoon social break, and a book of abstracts.
Agenda:
Thrustfest '98 Speaker Abstracts - Symposium Introductory Comments
by James G. Buchanan, Conoco Inc., Houston, TX
Predicting Structural Trap Geometries in Overthrust Belts by Shankar Mitra, ARCO Exploration and Production Technology, Plano, TX
Trap-forming structures in overthrust belts are commonly characterized by structural complexity and poor seismic data quality. Therefore, seismic data is usually insufficient to constrain the location and size of potential structural traps. Geologic and geophysical data, when combined with structural modeling and balanced cross section techniques can improve structural interpretations and thereby reduce trap risk for prospective structures.
Predictive models for interpreting structural styles must incorporate key geometric and kinematic characteristics observed in well-constrained surface and subsurface structures. Mechanical contrasts of key lithotectonic units play an important role in determining the type and geometry of fold-fault relationships, such as fault-bend, fault-propagation, and detachment folds. Lithotectonic packages with strong competency contrasts, such as thick carbonate units encased within thin shale units, result in fault-bend folds and duplexes. Examples of this structural style are found in the Sawtooth Range in Montana, the Canadian Foothills and the Southern Appalachians. Moderate to low competency contrasts, such as interlayered, thin-bedded sandstones characterized by high flexural slip efficiency, result in fault-propagation folds. Examples of these styles are found in the Polish and Romanian Carpathians. Over-thrust belts characterized by relatively competent packages overlying weak shales or salt typically result in disharmonic, detachment folds with related accommodation faults. Examples of this style are found in the Dinaride, Zagros, and Jura fold belts.
Delineation of deep anticlinal traps typically involves the extrapolation of surface and near-surface geometries to deeper horizons. Trap risks are related to changes in the geometry, location, and size of structures with depth. The relationship between the geometries of deep targets and near-surface horizons are dependent on the structural model, structural disconformities or changes in structural style. Therefore, a good understanding of the mechanical stratigraphy and its influence on structural geometry is critical in delineating poorly-imaged traps.
Structural Geometry of the Taconic-Acadian Thrust System in the Cambro-Ordovician of Western Newfoundland by Mark Cooper, PanCanadian Petroleum Limited, Calgary, Alberta, Canada
The Humber zone is the most external zone of the Appalachian orogenic belt in Western Newfoundland and records multiphase deformation of the Cambro-Ordovician passive margin and Ordovician to Devonian foreland basins by Taconic, Salinic and Acadian orogenic events.
The recent phase of exploration well drilling in western Newfoundland has provided new evidence for structural and stratigraphic models of the region. The first well drilled supported the hypothesis that the Round Head thrust had an earlier extensional history prior to the Acadian compressional inversion that created the present-day structural high of the Port au Port peninsula. The Port au Port #1 well penetrates the footwall of the Round Head thrust which has a significantly thinner Middle Ordovician section than in the hanging wall of the fault. The structure tested by the well is a small anticline caused by a footwall shortcut fault from the Round Head thrust. The second well was drilled some 40km to the NE to test the triangle zone discussed by previous workers in the area. This well demonstrates that the frontal monocline at the western edge of the triangle zone is elevated by a stack of imbricate thrusts composed of rocks of the Taconic allochthon. The age and facies of these imbricates suggest that they may have originated from the along strike equivalents of the Cow Head group which is exposed at outcrop some 130 km to the NE. Some of the elevation of the triangle zone is also due to inversion of basement involved extensional faults which have uplifted the Cambro-Ordovician carbonate platform. The third well was drilled in 1996 to test the up-plunge portion of the structure penetrated by the first well.
The structural model developed in the Port au Port area with the aid of these wells has been extended throughout the Humber zone in Western Newfoundland. The changes in structural style can be illustrated by a suite of regional cross-sections that show that prospective trap geometries are only developed in the southern part of the trend.
The reservoir model developed from these wells invokes exposure and karsting of platform carbonates on extensional fault footwalls during the Middle Ordovician. These structurally high fault footwalls became the foci of the dolomitizing and mineralizing fluids that utilized the major faults as fluid conduits.
3-D Visualization and Validation of Structures in Complex Compressional Terranes by Peter Bentham and Sandro Serra, Amoco, Houston, TX
Exploration for and production of hydrocarbons within compressional terranes continues to provide stiff challenges for our industry. Our ability to effectively acquire and analyze the data needed to make informed geotechnical decisions in such areas is inhibited by a number of geologic and non-geologic factors. It is crucial that the available data be used and integrated in a timely fashion, and that appropriate tools and technologies be applied during the evaluation process. The marriage of 2-D seismic data, balanced 2-D structural interpretations, surface outcrop and well-data is best done interactively within a dedicated three-dimensional environment.
Development of viable structural interpretations that integrate all of the available structural information requires a sound understanding of structural geologic concepts as well as an ability to rapidly evaluate complex geometric relationships in three-dimensions. Recently developed 3-D structural geologic tools are now available that allow an expert user to easily manipulate and integrate large volumes of data collected from both the surface and subsurface within compressional systems. The application of such tools, and how they have impacted the business of fold and thrust belt exploration within Amoco will be the subject of this presentation.
Geometric and Kinematic Tests of Contractional Fold Models Using Some Exceptional Natural Examples by Randall A. Marrett, University of Texas at Austin.
A wide variety of geometric models have been introduced to aid the interpretation of folds in the subsurface of fold-thrust belts, but the models have received little kinematic validation. Fragmentary data describing the geometry of a specific prospect-scale anticline typically can be modeled equally well using several different models, each of which implies a distinct kinematic development of the fold. The non-uniqueness of any interpretation in such cases results in two problems. First, an inadequate understanding of fold development limits the degree that one anticline favorably imaged by seismic profiling may be used to guide the interpretation of other anticlines or even the same anticline along strike. Second, without an understanding of fold kinematics, the impact of fold-related deformation on reservoir quality cannot be confidently assessed.
In order to study the applicability of fold models to natural folds, we have been using growth strata and strain markers to constrain fold kinematics in several exceptional surface and subsurface examples: the Monterrey salient and San Julian uplift of the Sierra Madre Oriental, Mexico; the Sardinero and Catemaco folds in the southern Neogene belt of Mexico and the Reed Wash fold train in the Cordilleran belt of Utah. Preliminary results from these folds suggest that the kinematic development of geometrically analogous folds may be different, and that the predictive capability of our geometric models is quite limited.
3-D Seismic Volume of a Buried Thrust Front, Foredeep to Emergent Thrust Sheets, Quiriquire Block: Improved Exploration and Production, Eastern Venezuela Basin by Vincent Rigatti, et al., Maxus, Dallas, TX
Sizeable 3D seismic surveys over buried thrust fronts provide the start of a full 3D work process that greatly improves the exploration and production efforts of multiple plays in complex geologic trends and maximizes their profitability. This full 3-D platform not only improves seismic imaging and interpretation, but allows continuous 3-D analysis of the projects; from structural modeling and mapping, to cost reduction efforts for well and development programs; to stratigraphic, structural and fracture modeling input for full field simulation and in fill drilling.
YPF/Maxus and its partners have achieved a full 3-D image of a buried thrust front in one of the most prolific hydrocarbon-bearing trends in the world with two merged 3-D seismic surveys totaling 550 km2 of surface coverage. This 3-D volume covers the series of stacked thrust sheets that form the eastward continuation of the Furrial field complex in the Eastern Venezuela basin. These data and the interpretive products were performed as a part of our technological commitment to Lagoven in the service contract of the Quiriquire block, awarded to Maxus in the 1993 Venezuela second marginal field bid round.
Lessons Learned from the Sikes Disposal Pits Superfund Site.
Abstract:
Sikes disposal pits Superfund site was an 185-acre uncontrolled hazardous
waste dump-the depository for a variety of chemical wastes created by nearby
petrochemical complexes during the 1960s. The site is located about two miles
southwest of Crosby, immediately north of old U.S. Highway 90 and roughly 20
miles northeast of Houston, Harris County, Texas.
The site is characterized by river alluvium overlying Texas coastal plain deposits. Shallow water-bearing zones occur in the alluvium. A second water producing zone is found in a sandy silt zone at about a 65 foot depth. The Chicot and Evangeline Aquifers occur below this zone, beneath several hundred feet of clay. The site lies within the 100-year floodplain of San Jacinto River.
The Record of Decision (ROD) for the Sikes disposal pit site called for onsite incineration of sludge and soils and treatment of contaminated water; this was accomplished in two phases. In the first phase (October, 1990 through January, 1992), the site was prepared for remediation, including construction of flood control structures, installation of a temporary incinerator, and construction of a water treatment facility. During the second phase, all wastes were incinerated eliminating the threats to human health and the source of contamination to the ground water; removal of treatment facilities and site restoration were completed in 1994.
Incineration is now finished, the incinerator facilities have been removed and the site has been planted with local grasses. The preliminary Close Out Report documenting completion of construction activities was signed in January, 1995. The final Close Out Report is issued and site deletion should occur in early 1998. O&M began in 1996, second year ground water monitoring was conducted in 1997.
Biographical Sketch:
Tom Davis served for three years as the on-site construction manager and was
later promoted to project manager for this two-phase, $116,000,000 hazardous
waste superfund site funded by two government agencies. In addition, he
supervised a health and safety inspection and provided oversight services on
behalf of Lockwood Andrews and Newman (LAN) to the TNRCC. LAN participated
in a joint venture that operated under a complex, multi-document contract.
Tom managed the project to closure; one of the first major superfund sites
successfully completed in the United States. This project won the highest
award in Texas for engineering and management from the Consulting Engineering
Counsel of Texas.
The Integration of Geochemical, Geological and Engineering Data to Determine Reservoir Continuity in the Iagifu-Hedinia Field, Papua New Guinea.
Date: Monday, June 15, 1998
Place: Westchase Hilton, 9999 Westheimer
Time: Social Hour 5:30 p.m., Dinner at 6:30 p.m.
Abstract:
Recent reservoir studies of the Iagifu-Hedinia field in Papua New Guinea have shown
the benefit of using a combination of geochemical, geological and engineering data.
Each type of data reflects a different characteristic of the reservoir compartments. The
combination of oil fingerprint and RFT pressure data demonstrates that some seals
have been effective over geologic time, while others are effective only during
production. The challenge to the evaluation of the Iagifu-Hedinia field is the result of
the structural complexity of the region and the lack of useful seismic data.
In Papua New Guinea, a series of oil and gas fields, including Iagifu-Hedinia, occur along the leading edge of the Papuan fold and thrust belt. Formed during Pliocene to Recent compression, they are structurally complex, and typically broken into multiple reservoir compartments. The presence of the karsted Darai limestone at the surface over most of the fold belt prevents acquisition of useful seismic data. Reservoir mapping, and establishment of reservoir continuity, is therefore based solely on surface geologic data, drilling data, dipmeter and RFT pressure data, well production histories, and geochemical correlation of reservoir fluids. During appraisal of the Iagifu-Hedinia discovery, these complimentary data sets demonstrated that a single hydrocarbon column existed above a flowing aquifer in the main block of the Iagifu-Hedinia field, a separate accumulation existed in the Iagifu 2X/8X block, and that two or more separate reservoir compartments existed in the Usano area.
Geochemical data have suggested the presence of reservoir compartments where other data were missing or inconclusive. Production history data has confirmed the geochemically based interpretations. Geo-chemical data suggest that oils at Iagifu-Hedinia have a common source. Slight differences in oil composition between reservoirs are likely due to variations in the reservoir filling history and multiple phases of oil expulsion from the same source rock.
Technology to Identify Reservoir Compartments In oilfield appraisal and development, a variety of tools are used to help understand future reservoir performance. Identification of reservoir compartments, whether vertical or lateral, is a critical part of this evaluation. Compartmentalization may develop over geologic time or during production depending on the characteristics of the seals which isolate the compartments. Frequently, the identification of many reservoir compartments are found only after the field is put on production. One very common measurement for detection of reservoir compartments is formation pressure. In the early stages of field development these pressures come from well tests (DST or RFT). Different pressure regimes is usually a good indication of reservoir compartments. In some instances though, small pressure differences may be difficult to detect or pressure data may be missing.
A particularly powerful tool complimentary to pressure data is comparison of the reservoir fluids themselves. This represents a direct measure of hydrocarbon continuity. The use of compositional data from PVT measurements as well as physical property data (gravity, bubble point and gor) are common. While the compositional data from PVT measurements are typically in the C1-C6 region, other methods can extend to considerably higher carbon numbers.
Geochemical methods are also well suited for reservoir compartmentalization studies. These methods utilize all the formation fluids, gas, oil and water. For oil analyses, gas chromatography can rapidly give a detailed analysis of the oil composition from C1 to about C35. Oil composition determined in this way is often referred to as a fingerprint of the oil. Comparison of these oil fingerprints is a direct way to evaluate the presence of reservoir compartments.
Biographical Sketch:
Russell Kaufman received his B.S in chemistry from the University of California at
Davis in 1972 and his Ph.D. in chemistry from the University of Colorado in 1977. He
joined Chevron Oil Field Research Company in 1978 and developed new tools for
reservoir geochemistry studies. After an assignment at Chevron Canada Resources in
Calgary, he joined Chevron Overseas Petroleum where he is currently a senior staff
geochemist.