摘要:

The assumption that all salt in the Gulf of Mexico basin is Jurassic demands a fixed structural framework since mid‐Jurassic time. This assumption has questionable geological support and is challenged.Salt in the Salina Basin of southern Mexico has been presumed Jurassic because shallow salt at Chinameca is overlain by ammonite‐bearing Kimmeridgian — early Neocomian limestones which, in turn, are overlain by Oligocene sediments.Despite numerous salt penetrations elsewhere in the Salina Basin, the Chinameca limestone has not been encountered. Instead, the non‐piercing salt massifs directly underlie Oligo‐Miocene beds, which have also been found intercalated with the salt. Two wells that have traversed the salt found Oligocene sediments below.Field checks in the Chinameca limestone type‐locality reveal that these beds are both strongly folded and heavily brecciated. They do not overlie the salt normally, and are interpreted as slumped masses that slid from elevated fault scarps onto Oligocene evaporites during Oligocene block movements.Geological evidence supports the conclusion that the Salina salt is Oligocene, and was deposited during the worldwide Oligocene eustatic drop. Because the Salina salt is stratigraphically continuous with the salt in offshore Campeche, this also is deemed to be Oligocene.The Challenger salt has been dated as Jurassic on the basis of one palynomorph‐bearing sample cored from the cap rock of the Challenger knoll. However, the Challenger salt is in continuity with the Campeche evaporites, which suggests that it, too, is Oligocene. In view of the wide range of datable detrital material recovered from Salina salt samples, the dating of Challenger salt from a single sample of insoluble residue cap‐rock is considered premature.On the north side of the Gulf, evidence for Oligocene salt obtained earlier from the Belle Isle salt dome is supported by the presence of intra‐Frio evaporites encountered in two deep exploration wells.The probability of large deposits of Tertiary evaporites in the Gulf of Mexico leads to the interpretation that the evolution of the Gulf Basin was governed by a sequential process of deep crustal extension that persists until the present day, rather than an exclusively Jurassic extensional event as is c

ISSN:0141-6421    

DOI:10.1111/j.1747-5457.1993.tb00102.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

TheSamgorifield in the Republic of Georgia (CIS) has produced more than 165 million brls of oil since its discovery in 1974, and the development of recently‐discovered deep gas is now under way. The field produces oil from an Eocene volcaniclastic section which has been interpreted as being associated with an island arc. Available data from the field include well logs, porosity and permeability measurements from cores, chemical analyses of fluids produced, and reservoir‐performance history. These data comprise the basis for an investigation of generation, migration and entrapment of hydrocarbons.TheSamgorifield provides evidence that requisite parameters for significant accumulations of oil and gas are present in Georgia. The existence of other large fields depends primarily upon the occurrence of suitable reservoir rocks. Volcanogenic rocks offer potential reservoirs, but the importance of enhanced secondary porosity development must be emphasized. Regional porosity within the volcaniclastic section has developed as a result of zeolitization coupled with fracturing, a situation evidenced by infiltration of meteoric water over large distances. In view of this, reasonable possibilities exist for the occurrence of similar reservoirs nearby. The ability to predict zeolitization and fracturing elsewhere in Georgia would be critical to exploration succ

ISSN:0141-6421    

DOI:10.1111/j.1747-5457.1993.tb00103.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

The Jiuxi (Western Jiuquan) Basin, located in the west of the Hexi Corridor, NW China, is a foreland basin which has been active since the Early Jurassic. It was formed as a consequence of the progressive northwards migration of the North Qilian thrusts in response to sinistral shearing along the 2,000‐km long Aerjin (Altun) Fault. Sedimentary deposits in the basin are controlled not only by foreland loading and thrusting, but also by the development of listric normal faults at high angles to the thrust belt. At the junctions of these two sets of faults, thick organic‐rich sediments and reservoirs have accumulated.During the Tertiary and Quaternary, thrusts propagated along the foot‐wall of the North Qilian Fault, truncating earlier‐formed oil pools and source‐rock layers and thereby causing great difficulties for petroleum exploration. A basin development model is proposed in this paper from cm integrated study of sedimentary fades, drilling and seismic data, structural analyses and cross‐section reconstructions.The average northwards movement in the frontal zone of the North Qilian Mountains since the Pliocene is estimated at about 8 mm/yr. Therefore, about one‐half of the Jurassic‐Cretaceous oil‐bearing basin could be buried beneath the Laojunmiao and North Qilian Marginal Faults, and is virtually untouched by drilling.Source rocks in the basin are black, lacustrine shales of Late Jurassic through Early Cretaceous ages, with a maximum thickness of up to 1.2 km in the Qingxi Depression. The generation of liquid hydrocarbons began in the Late Cretaceous or mid‐Oligocene; seven stratigraphical reservoirs, ranging in age from Silurian to Miocene, are described — anticlinal. fault‐ and “buried‐hill” structures are the most important traps.The petroleum potential of individual depressions is discussed, and suggestions for potential re

ISSN:0141-6421    

DOI:10.1111/j.1747-5457.1993.tb00104.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Numerous deep seismic and borehole studies have been made in the Dnieper‐Donets Paleorift (Ukraine), and, when combined with studies of oil‐ and gasfield distribution, indicate that there exists an interesting relationship between deep lithospheric structure and evolution, and the hydrocarbon potential of the Paleorift.It has been found that hydrocarbon accumulations tend to be associated with slopes in the Moho discontinuity, where most faults are located, and also where the basement and the lower layers of sedimentary cover have been fragmented by faults. These areas are the most promising for exploration.These facts could imply an abiogenic, mantle origin for oil and gas. Alternatively, the hot mantle ascending beneath the Dnieper‐Donets Paleorift may have created thermodynamic or fluid‐flow conditions within the sedimentary cover which were favourable for the transformation of biogenic material into oil and gas. In this case, mantle fluid‐flow along faults assisted the migration of hydrocarbons and its accumulation

ISSN:0141-6421    

DOI:10.1111/j.1747-5457.1993.tb00105.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

The paleoenvironments of the middle Miocene E2.0 Reservoir in theKolo Creekfield have been reconstructed in cores of Wells27and29from investigations of sedimentological and microfossil data. The sediments were examined for lithological features, trace fossils, mineralogical composition, diagenetic imprints, palynodéhris, palynomorphs and foraminifera, and these results were integrated with geophysical log data. Seven deltaic sub‐environments of deposition have been recognized: the distributary channel‐fill, lagoon/tidal flat, coastal barrier and delta fringe sub‐environments were common to both cores, while the prodelta was present in the core of Well27,and lagoonal and flood‐tidal deltas occurred in Well29.The sequence‐stratigraphic concept has been applied to these sub‐environments, and using the information from Wells27and29,well‐to‐well log correlation across the entire field allowed a reconstruction of the depositional history of the reservoir. The reservoir was deposited as one or two progradational parasequences during a high‐frequency highstand systems tract. There was more open vegetation and extensive development of lagoons/tidal flats in the western part of the field, but the overall depositional trend is similar to that of the prese

ISSN:0141-6421    

DOI:10.1111/j.1747-5457.1993.tb00106.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

This paper describes the use of heavy minerals and the characteristics of quartz grains in the study of three exploratory wells (149 core samples) in the northern Western Desert, Egypt.The studied sandstones are characterized by a predominance of tourmaline, zircon, rutile, anatase. epidote, garnet, monazite. staurolite and chlorite, in decreasing order of abundance. In general, there is no distinctive heavy‐mineral variation between Jurassic and Lower Cretaceous sands.Examination of the frequency distribution of the different types of inclusions in the quartz revealed that abundant rutile needles reflect a metamorphic terrane and a plutonic environment. Abundant tourmaline, microlites and devitrified magmatic relicts reflect acidic intrusive/extrusive parent rocks. The abundance of rutile with apatite and zircon is interpreted as being derived from host quartz of various parent rocks. The alteration in some inclusions (segmented rutile needles, spotted apatite and dark zircon) suggests possible dynamic disturbance of the area, resulting in the introduction of inclusions and devitrified and/or altered primary solid inclusions.It is concluded that the Jurassic and Lower Cretaceous sandstones studied were formed in areas characterized by an arid climate. These conditions led to the decomposition of both unstable and metastable heavy mineral

ISSN:0141-6421    

DOI:10.1111/j.1747-5457.1993.tb00107.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Zeolites and authigenic/diagenetic clay minerals in Neogene sandstones of the East Slovakian Basin are closely related to the presence of locally‐abundant tuffs and tuffaceous sediments. In tuffs, plagioclase crystals, glass shards, and volcanic rock fragments alter to zeolites and clay minerals. In sandstones, zeolites are formed both from the direct alteration of volcanic rock fragments, and as authigenic pore‐filling minerals; clay minerals occur as diagenetic products of both volcanics and feldspars. Zeolites present include erionite, clinoptilolite, mordenite, analcime, and minor offretite, phillipsite, and laumontite. Authigenic/diagenetic clay minerals include smectite, illite, chlorite, and kaolinite. Vertical and lateral distributions of authigenic/ diagenetic mineral assemblages tend to follow published models. A complete paragenetic model of the occurrences of these minerals within the basin is not currently possible with the present, limited database.Diagenetic/authigenic mineral suites in sandstone hydrocarbon reservoirs present special problems for exploration and production technology. These problems include: (1) well‐log distortions; (2) reservoir permeability reduction through diagenesis; and (3) reduction of permeability through interactions between diagenetic clay minerals and zeolites and incompatible fluid systems. Recognition of problematic mineral suites in this study allows for the application of accepted technological solutions, which in turn could result in the increase of recoverable reserves in addition to those added by exploration ef

ISSN:0141-6421    

DOI:10.1111/j.1747-5457.1993.tb00108.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

ISSN:0141-6421    

DOI:10.1111/j.1747-5457.1993.tb00109.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

ISSN:0141-6421    

DOI:10.1111/j.1747-5457.1993.tb00110.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Book reviewed in this article:“Basins on the Atlantic Seaboard: petroleum geology, sedimentology and basin evolution”. Geol. Soc.“Lacustrine basin exploration — case studies and modem analogs”, edited by B

ISSN:0141-6421    

DOI:10.1111/j.1747-5457.1993.tb00111.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY