Rim Syncline Research Articles

Thermal Anomalies in Sediments near Evolving Salt Structures: Importance for Modeling Timing of Oil Generation: ABSTRACT

ABSTRACT The temperature distribution through time in the subsurface has an important impact on the generation of hydrocarbons. It is therefore of interest to model the spatial variation of the temperature through time and the causes of the variation. The thermal conductivity of salt is a factor of two to three times higher than that of typical sediments. Salt structures provide paths of low thermal resistance for the conduction of heat from depth to the surface. The focused heat reenters the sediments near the salt apex so neighboring sediments are warmer than regional sediments, whereas sediments close to the salt base, and in the secondary rim synclines, are cooler than regional sediments. A combined self-consistent model of evolution of salt and sediments has recently been developed, so that the temperature distribution through time can be calculated. The relative thermal anomaly effects caused by height and width variations of salt structures are illustrated. The vertical extension of the oil window promotes earlier onset of maturation in sediments near the salt apex and delays conversion of trapped oil to gas in the deeper sediments when compared with the regional picture. The temperature history can then be incorporated with that of the modeled structural evolution of migration pathways and trap development, thus providing an integrated picture of the dynamic evolution of salt and sediments. Examples illustrate the importance of modeling thermal history in order to reduce hydrocarbon exploration risk near salt structures.

Salt and fault interactions in the northeastem Danish Central Graben: observations and inferences

Salt and fault interactions in the northeastem Danish Central Graben: observations and inferences

Interactive salt and sediment evolution: self-consistent quantitative models

Assessment of the combined evolution of salt and surrounding sediments is one of the major problems in salt-dominated basins. A quantitative approach, guided by observations from seismic and/or well data, is presented. The modeled present-day shape of a salt structure is constrained by an inverse non-linear procedure which determines the parameters controlling the salt shape. The non-linear procedure guarantees the shape to be in close correspondence with the observed present-day salt shape. By introducing time dependence of each of the parameters controlling the salt shape, the procedure permits an assessment of an evolving salt shape with time. By letting sedimentary beds move around the developing salt structure, the influence of the uprising salt on the evolving bed geometries above and around the salt is depicted. As the predicted present-day bed geometries must also be in accord with the observed rim syncline bed geometries, additional constraints are put on the parameters controlling the dynamic evolution of the salt structure. The inverse procedure automatically determines, in a self-consistent way, resolution and sensitivity of all parameters in the quantitative model, and also of the dynamic evolution of both the salt and the surrounding sedimentary formations. The procedure handles symmetric and asymmetric two-dimensional structures as well as symmetric three-dimensional structures. Applications are given to two salt structures in the North Louisiana salt basin. The first structure is a tall diapir with clearly defined rim synclines. By varying the parameters in the non-linear inverse procedure, a consistent reproduction of the observed data is obtained on both sides of the asymmetric diapir. In addition, in the regions where absence of data is greatest, the consistent model provides a measure of the degree, extent and location of allowed salt overhang in order that the observed and predicted salt shapes are in accord. Therefore, the procedure produces a quantified measure of the salt stock stem width to overhang width and the locations of both. The second structure consists of two salt pillows. Here the quantitative model provides a consistent picture of the dynamic shaping of each mound in relation to their common rim syncline. A synthetic case exemplifies the capability of modeling the combined salt-sediment evolution with the constraint that the depositional surfaces through time are horizontal. The modeled self-consistent dynamical evolution then permits a better understanding of evolving stress-strain, thermal focusing and hydrocarbon entrapment to be realized.

Physical modelling of overburden deformation around salt diapirs

Salt diapirs produce highly complex deformation patterns in the surrounding overburden which are difficult to image seismically or model numerically. To further the understanding of deformation around salt structures we have used physical models with brittle granular overburdens, and simulated sedimentation accompanying diapiric rise. Rigid linear indentors produce a crestal horst above the indentor with two flanking graben. Large amounts of indentation produce predominantly reverse faults along the margins of the diapir and extensional faults over the crest. In contrast hemispherical indentors produced inward-dipping concentric reverse faults. Forefully intruded polymer diapirs produce a narrow crestal graben above the diapir crest. Downbuilt polymer diapirs produce extensional faults on the flanks of the diapirs which offset the diapir walls. No clear secondary rim synclines were developed as polymer is withdrawn evenly from the whole of the polymer layer across the model. Strong and anisotropic layered overburden were simulated using cohesive clay and mica respectively. Detachments were formed along mica layers which suppressed faults with large throws. Cohesive layer deformation began with tensile fractures, permitting rotation of fractured rafts around the sides of the diapir. These progressively slip off the crest and create large gaps in the stratigraphy.

天北・羽幌地域の石油地質 深部構造特性と炭化水素ポテンシャル

The thick Cretaceous-Tertiary sediments which cover the Tenpoku and Haboro area, the northern part of Hokkaido, is believed to possess substantial hydrocarbon potential. More than seventy anticlinal structures have been recognized in this area, but to date only eight wells have penetrated the Paleogene section while four have drilled to Cretaceous sediments.Four types of anticlinal structures are recognized as interpreted from well data and seismic profiles. The Kitakawaguchi feature represents the first type of anticline. Two wells have been drilled on this structure and seismic profiles are available. A gentle antiform exists as the Paleogene section drapes across thrust-faulted Cretaceous sediments. A more pronounced Neogene anticline is superimposed upon the pre-existing structure. The later structure was formed by flowage of Miocene shales and associated thrust-faulting. The Miocene shales exhibit abnormally high pressure and steep dips. Small rim synclines commonly exist on the flanks of this type of structure.The Uttsu Anticline illustrates the second type of anticlinal feature. The MITI Enbetsu well was drilled to test this structure. The anticline was formed by deep-seated vertical thrust-faulting which affected Paleogene and Cretaceous strata. The formation of the anticline produced an important effect on Tertiary sedimentation. Similar features are thought to exist along the Horonobe and Magaribuchi-Toyotomi fault systems.The Rikibiru structure is an example of the third type of anticline and is located in the southern part of the study area. The MITI Rumoi was drilled on the western flank of the feature. Dipmeter logs indicate that this deep Cretaceous structure is quite huge and broad with gently dipping flanks. The thick sequences of coarse-grained Miocene sediments deposited in this area contrast with the predominantly shaly strata seen to the north. The formation of the Rikibiru Anticline is thought to have formed due to loading of the thick Miocene section. Shale flowage did not occur in this area due to the lack of thick shale sequences.The Maruyama Anticline illustrates the fourth type of anticlinal structure. No wells have been drilled to date on this type of feature. These anticlines are broad and gentle-dipping and are surrounded by rim synclines similar to those exhibited by the first anticline type.Growing mechanism, timing and distribution of each type of anticline are discussed with the view of petroleum geology.

Dynamical Evolution and Overhang Development of Salt Structures in the North Louisiana Salt Basin: Quantitative Models

ABSTRACT Applications are given of a novel quantitative inverse modeling procedure to two salt structures in the North Louisiana salt basin. The first structure is a tall diapir with a clearly defined rim syncline to one side of the diapir and a less well defined rim syncline on the other side. By varying the parameters in the non-linear inverse procedure, a consistent reproduction of the observed data is obtained on both sides of the asymmetric diapir. In addition, in the regions where absence of data is hardest felt, the consistent model provides a measure of the degree, extent, and location of allowed salt overhang in order that the observed and predicted salt shapes are in accord. Therefore the procedure produces a quantified measure of the salt stock stem width to overhang width and the locations of both. The second structure consists of two salt mounds. Here the quantitative model provides a consistent picture of the dynamic shaping of each mound in relation to their common rim syncline. In addition the inverse procedure provides a self-consistent dynamical evolution for both salt and sediments taken together which will be discussed.

Quantitative Modeling of the Dynamic Evolution of Salt Structures

ABSTRACT Assessment of the combined evolution of salt and surrounding sediments is one of the major problems in salt-dominated basins. A quantitative approach, guided by observations from seismic and/or well data, is presented. The present-day shape of a salt structure is constrained by an inverse non-linear procedure which determines the parameters controlling the salt shape. The shape is shown to be in close correspondence with the observed present-day salt shape. By introducing time-dependence of each of the parameters controlling the salt shape, the procedure permits an assessment of an evolving salt shape with time. By letting sedimentary beds move around the developing salt structure, the influence of the uprising salt on the evolving bed geometries above and around the salt is depicted. As the predicted present-day bed geometries must also be in accord with the observed rim syncline bed geometries, additional constraints are put on the parameters controlling the dynamic evolution of the salt structure. The inverse procedure automatically determines, in a self-consistent way, resolution and sensitivity of all parameters in the quantitative model, and also of the dynamic evolution of both the salt and the surrounding sedimentary formations. The procedure also handles asymmetric two-dimensional structures as well as symmetric three-dimensional structures. Introduction of basement heat flow permits assessment of the thermal focusing effect of the evolving salt relative to the surrounding sediments which, in turn, permits an estimate of the timing of maturation of possible source rocks, migration and possible trapping below salt overhangs, or in reservoirs developed above and along the flanks of the salt.

The development of salt structures in Denmark and adjacent areas: the role of basin floor dip and differential pressure

Most of the North Sea region is underlain by Permian salt deposits, and many hydrocarbon accumulations are related to salt structures. It is therefore important to understand salt tectonics. Numerous articles have been published on salt teetonic subjects, including model studies by Parker and McDowell (1955), salt migration in northern Germany by Trusheim (1960), salt stock families by Sanneman (1968), salt structures in the Gulf region in the book by Halbouty (1979), the effect of differentialloading in the Gulf region by Bishop (1978), coupling between sedimentation and rim synclines by Seni and Jackson (1983a,b), and several studies from the North Sea region by Jenyon (1985,1986,1987,1988).

Architectural features of the Kayenta formation (Lower Jurassic), Colorado Plateau, USA: relationship to salt tectonics in the Paradox Basin

Fluvial sandstones of the Kayenta Formation were analyzed using architectural element analysis. Paleocurrent trends, the distribution of lacustrine facies and local silcrete development indicate that synsedimentary movement of evaporites in the underlying Paradox Basin created an unstable basin floor beneath the Kayenta fluvial system. This instability resulted in deflection of fluvial axes, local basin development and local areas of interrupted fluvial deposition with eolian dunes. Paleocurrent trends in the Kayenta system reflect periodic interruptions of southwesterly flow. Salt migrating laterally out of a rim syncline into an adjacent salt anticline resulted in a rim syncline of slight topographic relief. The resulting basin was probably rapidly filled, allowing the resumption of southwesterly flow. Differential movement of salt (incipient solution collapse features (?)) resulted in the formation of small centripetal basins in which playa mudstones formed. A laterally extensive resistant ledge underlies a horizontal surface, suggestive of deflation to the water table of an exposed section of valley fill. A channel scour in the top of one of these surfaces has margins much steeper ( > 60°) than the angle of repose for unconsolidated sand. Early cementation of the exposed floodplain could account for this resistance.

The Vredefort structure: estimates of energy for some internal sources and processes

The conspicuous features of the Vredefort structure are the concentric arrangement of gneissose core, steeply dipping metasediments and metavolcanics and a peripheral rim syncline; the alkali intrusive suite and its metamorphic aureole; the indicators of fracturing and high pressure (shatter cones, coesite and stishovite, and microscopic deformation textures); and the predominance of CO 2 over H 2O in fluid inclusions in the gneissose core. The cause of the Vredefort structure lies in either external or internal agencies; possible internal agencies and sources of energy are discussed here. In reviewing possibilities, a continuum is recognized between two extremes: at one extreme the major sources of energy are taken to be the density inversion (metasediments overlying granitic gneiss) and the alkali intrusions, whereas at the other extreme the major source of energy is taken to have a deep-seated and explosive character, most of the energy being liberated in one or two short, but very great, bursts. Between the extremes lie scenarios in which violent energy releases form substantial, but not overwhelming contributions to the total. Attention is focused initially on the less explosive end of the range: the hypothesis explored is that the gneiss rose because of buoyancy, while being disturbed and accelerated by the alkali intrusions. The aspect selected for emphasis is the energy budget; quantities of energy are estimated as follows: (1) Gravitational energy available from the density inversion, —10 21 J, (2) thermal energy associated with the alkali intrusions—10 21 J, and (3) energy consumed in forming shatter cones—10 15 J. (By comparison, for Mount St. Helens in April–May 1980 the estimates are: thermal energy associated with magma—10 18 J, and energy released in four major seismic events—10 13 J.) In addition to the energy budget, aspects requiring attention are the apparent compressive stress intensities (8–10 GPa to form stishovite) and the form and distribution of the shatter cones. Possibilities are (1) for stishovite, that sufficient compressive stress developed locally at asperities on fracture surfaces, and (2) for the cones, that they formed by quasi-static Mohr-Coulomb fracture in radially symmetrical local stress fields produced by seismic pulses of magmatic origin imposed on rocks already prestressed during gravity doming. With regard to the role of compressed volatiles, they may have been important in affecting fracture behavior, preserving stishovite by quenching and promoting development of certain microdeformations at low stress levels. Their relative importance as a source of energy, in comparison with the other sources mentioned, is not brought out by the calculations. Nothing in the above is intended to exclude other possible reconstructions from consideration, the method of multiple working hypotheses being upheld.

Impact on Hydrocarbon Retention of Sedimentary Fracturing and Faulting Around Salt Domes and Salt Sheets in Gulf Coast: ABSTRACT

Emplacement of diapiric masses can have a profound effect on the structure of the formations overlying the diapir and on the formations being intruded. This influence may be manifested in many ways, such as the deformation of these formations to accommodate the intrusion, development of faulting in the supradomal formations, modification of the depositional pattern resulting in thinning of beds as one approaches the dome, and the development of a rim syncline at depth. These features may, in turn, also impact the further development of the salt diapir and may also create an environment favorable for the trapping of hydrocarbons. In this paper, the authors present a model of the initiation of faulting in the formations overlying a salt diapir that is being emplaced at depth. A proposed technique to estimate the stress induced in the formations surrounding the uprising dome is based on analysis of the deformation induced in these formations and is expected to be valid for small to moderate levels of deformation. To underscore the physical processes that are operating, they invoke a model of the deformation of the sedimentary formations surrounding a salt dome; however, this analysis may also be extended to the situation where themore » deformation of the formations is estimated from the available observational data. Having specified the deformation of the sedimentary formations, they then infer the stresses that generated these deformations through application of the theory of elasticity. In this way, they can model the state of stress in the formations surrounding a salt dome during the time in which the dome is being emplaced.« less

SOME DEFORMATION EFFECTS IN A CLASTIC OVERBURDEN RESULTING FROM SALT MOBILITY

In a basin containing an evaporite sequence that includes salt rock, should the salt become mobile and deform plastically, it will produce important structural effects in overlying sediments. These effects may include folding, faulting, slumping, and in some cases where dissolution of the salt also occurs, collapse structures. The movement of the salt/overburden system during plastic deformation of the salt may be syndepositional, in which case rim syncline sedimentation will take place at the surface. The form taken by the rim syncline deposits will be related to the stage of development of the salt structures with which they are associated.An understanding of the mechanisms involved is important, particularly in a basin containing hydrocarbons. Also, study of the behaviour at depth of sediments which are subject to deformational stress may assist in solving structural problems on the Larger, regional scale. Selected examples of various effects seen in the North Sea Zechstein salt basin are discussed and illustrated with recently‐acquired seismic data.

Buoyancy‐driven instabilities of low‐viscosity zones as models of magma‐rich zones

The low Reynolds number dynamics of a thin layer of fluid bounded below by a flat horizontal boundary and above by a fluid of another viscosity and greater density is reported. Three distinct stages of growth were observed. The first stage is a Rayleigh‐Taylor instability, in which disturbances of one specific wave number grow most rapidly. If ε is the ratio of the viscosity of the thick layer to the viscosity of the thin layer, fastest growth is for wave number ε−⅓. In the second stage, distortion of the interface is large, and it is found experimentally that the fluid moves out of the thick layer as circular columns surrounded by relatively broad regions of descending material. In the third stage, fully matured structures are formed. If the upwelling material has less viscosity than the surrounding material, the structure develops a rim syncline and a pronounced overhang and eventually ascends as a spherical pocket of fluid fed by a conduit. Two applications to geophysics are given: The first application follows from the fact that a melt source must exist in the mantle below mid‐ocean ridges. This source can be approximated as a cylindrical body with lower viscosity and density compared to the overlying mantle. If the cylinder develops a gravitational instability, it will develop regularly spaced vertical protrusions. Estimates of the spacing are compared to high‐resolution segmentation data, and some constraints on viscosity of the mantle below spreading centers are made. These are that viscosity of the mantle is 1018±1 P, and the ratio of this viscosity to the viscosity of the cylinder is less than 100. In the second application, the upwelling conduits are measured experimentally and solitary waves are observed. A recently found analog with magma rising up through the pores of a viscous crystalline matrix is discussed.

The Fulmar Oil-field (Central North Sea): geological aspects of its discovery, appraisal and development

The Fulmar Oil-field (Central North Sea): geological aspects of its discovery, appraisal and development

Physical Modeling of Sedimentation Adjacent to Diapirs and Comparison with Late Precambrian Oratunga Breccia Body in Central Flinders Ranges, South Australia

The interaction of sedimentation with the change in shape of a developing diapir is modeled in a series of simple sandbox experiments. This model replicates the pillow, diapir, and postdiapir stages of salt movement. Modeling produced rim synclines, crestal unconformities, and turtle-structure anticlines--all features known to be associated with diapirs. By changing experimental parameters such as diapir shape, sedimentation was simulated around various diapiric situations. One experiment closely matches the sediment distribution around the Oratunga diapir, one of the controversial breccia bodies in the late Precambrian-Cambrian Adelaide geosyncline exposed in the Flinders Ranges of South Australia. Rim synclines, unconformities, and bedding attitude around Oratunga resemble those described around salt domes. In addition, the distribution, size, orientation, and lithology of breccia within the Oratunga diapir resemble breccia associated with active salt diapirs in Iran. These data suggest the breccia was emplaced as a salt diapir.

Possible Salt Movement in Northern Wasatch Plateau: ABSTRACT

The Jump Creek 7 ½-minute quadrangle in the northeastern Wasatch Plateau is an area where Late Cretaceous to early Tertiary formations are fractured by at least two complex systems of faults. Southern and eastern sections of the area are dominated by north-south-trending faults, such as the Gordon Creek fault zone, whereas the northern section is dominated by northwest-southeast-trending faults. Strong evidence, including horst and graben structures, rim synclines, and other collapse-related features, suggests that north-south-trending faults may be related to salt movement within the underlying Jurassic sediments. Indeed, the Gordon Creek fault zone could represent part of the eastern boundary of the Arapian evaporite basin. The northwest-southeast-trending faults appear to parallel major lineaments that cut across the Wasatch Plateau, Book Cliffs, and San Rafael swell areas and suggest origins not related to salt tectonics. This fault system, however, may be part of these lineaments that have been accentuated by the salt movement. The possibility of the structures in the Jump Creek 7 ½-minute quadrangle producing excellent hydrocarbon traps cannot be overlooked. Structures similar to those found in this area are proven producers in Joes Valley and Pleasant Valley fields, both located within several miles of the Jump Creek quadrangle. End_of_Article - Last_Page 938------------

Domes of East Texas: ABSTRACT

Data have been collected in the last 5 yr on the 15 salt diapirs that extend upward to shallow depths (4,000 ft or 1,220 m) in the East Texas basin. These salt diapirs penetrate Jurassic and younger units and have controlled their deformation in the central part of the basin. Both primary and secondary data have been gathered. Primary data are observations of dome shape, depth, structure, and resources. Examples of primary data are depths to cap rock and salt, cross-sectional area, axial ratio, crestal area and percentage of planar crest, axial plunge, tilt azimuth and distance, structural symmetry, side convergence, and overhang azimuth and percentage, as well as a new quantitative classification of dome shape. The structural styles of strata around each dome can be desc ibed in terms of the size of the rim syncline and drag zone around the diapir, angular relations between the strata and the salt, and style of faulting. Secondary data include deductions and inferences based on the primary data. The growth evolution developed from the pillow stage, through the diapir stage, to the post-diapir stage. Unconformities resulted from erosional breaching of the dome in the past. The structural stability and hydrologic integrity of each dome have been assessed in terms of the age of the most recent deformation. Geomorphic and hydrologic evidence for dome uplift, subsidence, or brine leakage are included in a new classification of drainage patterns above domes. End_of_Article - Last_Page 1213------------

Gibsland Salt-Stock Family in Northwestern Louisiana: ABSTRACT

A semiregional isopach map of the Hosston-Sligo interval in north Louisiana suggests the existence of a salt-stock family similar to D. Sanneman's example in the Zechstein basin of northwestern Germany. The mother salt appears to be the Gibsland salt dome in Bienville Parish, which the isopach map indicated had a well-developed rim syncline during Hosston deposition. Withdrawal of salt into the Gibsland dome appears to have triggered the growth of peripheral salt pillows such as Vacherie, Minden, Athens, Sugar Creek, and Arcadia. Some of these pillows subsequently developed into salt stocks. The centrifugal or outward growth of salt structures continued with the withdrawal of salt from beneath the Minden subbasin into the Minden and Bistineau salt domes. This acce tuated growth of the Sligo, Bellevue, and Cotton Valley salt pillows, which in turn triggered development of the Pine Island salt pillow in latest Early Cretaceous time. The growth of the salt structures progressed outward from deeper to shallower portions of the North Louisiana salt basin. An older salt-stock family may be centered on the Winnfield or Cedar Creek salt domes in the deepest part of the salt basin. Centrifugal growth of these stock should be discernible in seismic profiles. A knowledge of the relative ages of these structures is important in predicting sites of Lower Cretaceous reefs and hydrocarbon migration paths. End_of_Article - Last_Page 1219------------

Exploration Significance of a Possible Subsurface Meteorite Impact Feature in Garfield County, Montana: ABSTRACT

Geophysical information gathered near the western edge of the Williston End_Page 1347------------------------------ basin by ARCO Exploration Co. indicates the presence of a structural anomaly resembling a meteorite impact feature. Many anomalous features believed to be subsurface astroblemes are documented in the literature. Controversy exists concerning these astroblemes, not only as to their existence but also to their potential as hydrocarbon reservoirs. There have been many hypotheses generated concerning the origins of such structural anomalies. Upon examination of the seismic data, surrounding well control, and literature, the most reasonable interpretation remains that of an astrobleme. ARCO's Chimney Prospect, located in Garfield County, Montana, has seismic features similar to those seen at Red Wing Creek field, a well-documented probable astrobleme in North Dakota. These similarities formed the basis for the interpretation of Chimney Prospect as an astrobleme feature. Both impacts occurred in the Jurassic, and seismic evidence indicates that neither feature resulted from basement tectonic movement. Seismic data also indicate that Chimney Prospect has a central uplift with approximately 250 ft (76 m) of structural closure. It is surrounded by an identifiable rim syncline and a much less developed outer rim. Chimney Prospect encompasses approximately 2,000 acres (800 ha.). The time of impact has been determined to be Jurassic, with deformation found in pre-impact se iments as old as the Mississippian Kibbey Formation. The deposition of post-impact sediments has been affected by the rebound of the central uplift. The ARCO Coastal/BNRR 1-9 Skeleton Creek, located 3 mi (5 km) southeast of the prospect, has been used as a control well representing normal nonimpact sedimentation in the region of the anomaly. Chimney Prospect has been tested by the ARCO-1-1 BNRR/Coastal well. No significant hydrocarbons were encountered. Geologic evidence indicates that a small meteorite landed in a shallow Jurassic sea impacting soft, plastic sediments which dispelled much of the impact force. The underlying sediments at the time of impact were elastic enough to brecciate. Subsequent to impact, the open fractures were either healed or filled with calcite, thereby destroying the porosity and permeability in the potential reservoir prior to oil migration. By contrast, the fracturing at Red Wing Creek field was more extensive because the meteorite body was larger; and it impacted more brittle, lithified carbonates. Using Donofrio's classification system, Chimney Prospect must be considered to be a possible rather than a probable meteorite impact crater. Borehole samples did not confirm the presence of any shock metamorphic features. The occurrence of astroblemes in the subsurface is rare. When detected, five main criteria must be met to enhance the possibilities of an economic reservoir: (1) a meteorite body of sufficient size and velocity to produce a brecciated reservoir, (2) preservation of open fractures and pore space through time, (3) effective seals for trapping hydrocarbons, (4) oil migration after impact and deposition of the seal, and (5) open-minded management aggressive enough to drill such features. One obviously does not actively explore for these features; however, once stumbled upon, they should be considered as an unusual opportunity to explore and test for hydrocarbons. End_of_Article - Last_Page 1348------------

The Dummy Creek association: rim syncline deposits

The Dummy Creek association: rim syncline deposits