ISSN:0141-6421    

DOI:10.1111/j.1747-5457.1995.tb00913.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

The restoration of sections involving salt structures is complicated, because it is often difficult to understand fully the dynamics of the system. The occurrence of hydrocarbons is often associated with traps in the vicinity of, or directly adjacent to, salt structures; different methods to delineate the combined evolution of salt and sediments have therefore been developed. Because dynamical parameters are rarely known more accurately than within an order of magnitude, intrinsic uncertainties are introduced in any model based on assumptions concerning the dynamical behaviour of salt and sediments.A quantitative approach is presented here, guided by observed geometries of the salt‐sediment interface and of the bed horizons from seismic and/or well data. This novel procedure considers the salt‐sediment system as composed of geometric shapes that are allowed to vary with time when calculating the salt‐sediment evolution. 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. Because the predicted present‐day bed geometries must also be in accord with applied control criteria (such as the change in salt volume with time, the geometry of the depositional surface with time, and the compaction history), additional constraints are put on the parameters controlling the evolution of the salt shape.The capability of being able to follow the changing bed geometries with time allows the strain in the sediments through time to be traced. The stresses that generated the deformations in the sediments can then be inferred through application of the theory of elasticity. Furthermore, the combined evolutionary picture may be used to assess thermal “focusing” through time by a highly conductive salt structure, because the salt and bed geometries are known at each instant.A case history from the North Louisiana Salt Basin shows aspects of different combinations of control criteria on salt‐sediment evolution. Information is thus provided on the importance of evaluating the data and control criteria necessary for constraining the possible evolution histories.It is suggested that the novel inverse procedure presented here will improve understanding of the combined evolution of salt and sediments, and is therefore of significance in hydrocarbon

ISSN:0141-6421    

DOI:10.1111/j.1747-5457.1995.tb00914.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

The supercontinent of Gondwana (Antarctica, Africa, Australia, South America, India, the Arabian Peninsula, Madagascar and Sri Lanka) covered more than six times the combined area of the United States and Brazil. In this paper, the petroleum occurrences and potential of glacially‐related rocks of Carboniferous‐Permian age in this vast area are reviewed in terms of basin types, reservoirs, seals, traps and source rocks.Significant amounts of heavy oil, sourced by Precambrian algal‐rich shales, are produced from glacially‐related sandstones in some 20 fields in Oman. Bolivia has 27 oil‐ and gasfields sourced from underlying Devonian shales, and oil production occurs in two fields in nearby Argentina. In Australia, there is production from two basins: the Cooper Basin has 24 productive fields (mostly gas), and the Canning Basin has six small fields. In Brazil, four non‐commercial shows have been found in the Paraná Basin and one in the Amazonas Basin. In Paraguay, southern Africa and India, there is no production from glacially‐related sandstones.Production and shows occur in cratonic basins either in the interior or along the margins of Gondwana, except for those in Bolivia, Argentina and South Africa, which occur in foreland basins.Sandstone reservoirs were deposited mostly as glacial outwash, as small deltas, either in lakes or marine basins, or as turbidites in marine basins bordered by continental ice sheets. Seals are diamictites, mudstones, shales and possibly diabases in the Paraná Basin. Traps include tectonic and salt‐related anticlines as well as pinch‐outs against glacial channels. Glacial outwash and glacio‐marine sandstones are thus important petroleum exploration targets.Commercial production to date is sourced from both older and younger non‐glacial beds. The fields in Oman were sourced by Precambrian algal‐rich shales, and those in Bolivia and adjacent Argentina by Devonian and possibly Silurian organic‐rich shales. The source of the gas in the Cooper Basin is from overlying coal beds. Neither modern marine, high‐latitude muds nor ancient glacially‐influenced marine shales contain sufficient organic material to be considered adequate source rocks.This review indicates that petroleum production in Gondwana's glaciogenic deposits mostly occurs in cratonic and passive margin basins; it occurs wholly in sandstone reservoirs, chiefly in structural traps, and nearly everywhere, reservoirs are sourced by hydrocarbons from non‐glaciogenic shales (either older or younger). The only “glacially unique” features of petroleum in Gondwana deposits are its seals of diamictites, which surely must also be true when considering the petroleum possibilities of older ancient glac

ISSN:0141-6421    

DOI:10.1111/j.1747-5457.1995.tb00915.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Oilfields in the Middle Jurassic Brent Group of the East Shetland Basin contain abundant quartz cement, which reduces porosity by 10–15%. This quartz cement is believed to have started to grow at depths of around 2‐3km. Oxygen isotope signatures in diagenetic quartz imply that it grew from meteoric pore waters; however, fluid inclusion temperatures are 30–50d̀C higher than temperatures which should have prevailed at the inferred palaeo‐depth. Large‐scale circulation of hot water has been proposed to explain this “temperature anomaly”, but this is geologically difficult in terms of heat and fluid budgets. Finite‐element fluid‐flow models of a generic fault‐block rift‐basin stratigraphy are used to evaluate two alternative hydrogeological models for deep quartz diagenesis in Brent Group sandstones:1Meteoric waters may have penetrated several kilometeres into the crust before rising rapidly as a hot, isotopically‐evolved fluid;2Cool meteoric waters from the palaeo‐land, fed directly into the Brent Group aquifer, moving tens of kilometres laterally into the basin.Numerical models show that in this case gravitational penetration of moving fluids to considerable depth in the crust was indeed feasible with a driving head of only 200 m. Fluid velocities were so low (≅ 0.01 m/yr) that the heating effects of the fluids were minimal. Long‐range lateral transport of heat was also inefficient, for fluids tend to emerge along the first major fault plane encountered. Large‐scale mixing within aquifers resulted in a uniform fluid during the start of quartz diagenesis in the Brent Group. This mixing was not sensitive to permeability anisotropy. The slow infiltration of meteoric fluids into Brent Group aquifers is inferred to have maintained a low‐salinity, meteoric isotopic dominance to the pore fluids. These slow, large‐scale lateral flows may have exited from the Brent aquifer at “leak points” on shallow‐buried structures, such as Gullfaks. Degraded oil on the downdip side of Gullfaks also independently suggests an active deep aquifer in the Early Tertiary. Consequently, diagenetic quartz grew at equilibrium temperatures and adopted a meteoric‐dominated isotopic signature. Quartz supply was decoupled from s

ISSN:0141-6421    

DOI:10.1111/j.1747-5457.1995.tb00916.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

The Jirani Dolomite was formed during a major relative fall in sea‐level in middle Ypresian (early Eocene) times, in shallow, hypersaline lagoons on a restricted shallow platform, where supretidal and intertidal and semi‐arid to arid conditions prdominated. Localisation of the shallow logoonal facies to the region of the Jifarah Trough suggests that restriction was caused by downwarp relative to mild uplift of the Jifarah Platform to the north.Two main facies are recognised: and anhydritic dolomite facies, composed of dolomite and dolomitic limestone with anhydrite nodules; and a non‐anhydritic dolomite faices, composed of dolomite and dolomitic limestone only. Lithologic and petrographic evidence leads to the conclusion that anhydrite was also present in the non‐anhydritic dolomite facies initially, but was removed by dissolution processes. Petrographic studies show that dolomitisation proceeded in three stages. Stage I involved penecontemporaneous/early8 diagenetic dolomitisation of the precurosr limestones with gypsum/anhydrite under hypersaline seepage reflux conditions. Stage II dolomitisation, mainly confined to the non‐anhydritic dolomite facies, was probably formed in the mixing zone between meteoric and sea water, probably at shallow depths of burial. Stage III dolomitisation occured at depth in the late stage of basin evolution, causing some infilling of mouldic and vuggy porosity by coarsely crystalline, saddle dolomite. Evidence of mixing zone dolomitisation indicates that the Jirani Dolomite was exosed subaerially. Studies of the Metlaoui Group show that this event can be related to a major relative fall in sea level in early Lutetian times following deposition of the Jdeir Formation. Exposure of the deposits to flushing by meteoric waters explains the dissolution of the anhydrite from the non‐anhydritic dolomite faices, and the accentuation of the well‐development porosity in this facies, which make it one of the most important reservoir rocks in the of

ISSN:0141-6421    

DOI:10.1111/j.1747-5457.1995.tb00917.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

The PreCaspian (North Caspian) Basin is located on the SE margin of the Russian Platform, and extends as far south as the north coast of the intra‐continental Caspian Sea. Regional surface elevations here are as much as 24 m below sea‐level. The basin is one of the World's deepest, with basin‐fill sediments exceeding 20 km in thickness. The Proterozoic section, the pre‐slat Palaeozoic section, and the Upper Permian (slat‐bearing) interval are all about 5‐km thick, although as a result of salt movements, the salt‐bearing sequence may be thicker. The basin has a roughly oval outline, and is 900‐km wide, 600‐km is length, and covers around 500,000 sq. km. It is divided into the Central and SE Sub‐basins by the approximately east‐west trending Astrakhan‐Aktyubinsk system of basement highs. A series of massive carbonate build‐ups rim the basin margins.This paper considers the sturcture and hydorcarbons potential of the pre‐salt (Palaeozoic) sedimentary section, whose regional prospectivity has been confirmed by the discovery of a series of “giant” oil, gas and condensate fields, including Tengiz, Karachaganak and Astrakhan. Hydrocarbons in these fields are sourced and reservoired in massive organicri

ISSN:0141-6421    

DOI:10.1111/j.1747-5457.1995.tb00918.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Petroleum Systems are currently being studies within the general framework of plate tectonics. This new approach has led to the definition of three types of system in the context of the dynamic evolution of sedimentary basins. These three types are “initial rift”, “continental platform”, and “orogenic‐deltaic” Petroleum Systems. The richness and efficiency of a petroliferous basin often depends on an association between two, or perhaps all three, of these types of system. Foreland basins are perhaps the best example.Plate‐tectonics theory suggests that a mobile lithosphere is the rule rather than the exception. The transfer of both fluids and materials may occur within a sedimentary basin as a result of horizontal or vertical displacement of the lithosphere. Petroleum Systems therefore appear to be a direct consequence of crustal mobility.When hydrocarbons migrate out of a source rock, they may either be dispersed within another lithological unit and effectively “vanish”, be lost by seepage into the atmosphere, or be trapped by some sort of permeability barrier. In the latter case, the resulting hydrocarbon accumulation can be described as a temporary concentration, whose duration essentially depends on the intensity of the incoming fluid flow and the resistance of the permeability barrier(s).The study of a particular Petroleum System within a global geodynamic framework enables the richness (or otherwise) of the oil province in ques

ISSN:0141-6421    

DOI:10.1111/j.1747-5457.1995.tb00919.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

ISSN:0141-6421    

DOI:10.1111/j.1747-5457.1995.tb00920.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Book reviewed in this article:“Middle East Petroleum Geosciences—GEO'94, vols I and II”. Selected papers from the Middle East Geosciences Conference, Bahrain, April, 1994. Edited by M. I. Al‐H

ISSN:0141-6421    

DOI:10.1111/j.1747-5457.1995.tb00921.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY