摘要:

Since 1972, numerous large and giant fields have been discovered in the Reforma area of Chiapas and Tabasco States, southern Mexico, and on the offshore Campeche shelf west of Campeche State. The huge carbonate bank with which these discoveries are associated is called the Great Carbonate Bank of Yucatán. Most of the Reforma fields produce from bank‐edge talus, now largely dolomitized, of Late‐Jurassic and Early‐ to Middle‐Cretaceous ages, and drilling depths to the tops of the reservoirs generally range from 3,800‐4,500m. The offshore discoveries include fields which are productive mainly in bank‐edge talus of Paleocene and Late‐Jurassic ages, and depths to the top of production generally are shallower than onshore‐1,260‐3,500m. The petroleum source materials for the Jurassic, Cretaceous, and Paleocene fields are believed to be mainly in Late‐Jurassic strate, but some Early‐Cretaceous sources cannot be eliminated. Middle‐Cretaceous rocks have not yet been identified beneath the offshore shelf from Tampico (Arenque) to Samaria (A. J. Bermúdez) and Conduacán. Although most of the discovered fields contain mainly oil, some of the fields contain gas and condensate.Some porosity and permeability is primary, and most is secondary‐the result of solution, dolomitization, and intense microfracturing. The original trap for the Late Jurassic‐Middle Creataceous fields appears to have been stratigraphic, but the present traps are mainly fractured and faulted domal salt pillows created during the Laramide orogeny.The basis for the discovery of the fields was the widespread presence on the Yucatán Peninsula, and in the States of Campeche, Chiapas, and Tabasco, of Cretaceous through Tertiary backreef or lagoonal facies‐carbonates, anhydrite, and some halite, The drilling of the Pichucalco well in 1971 for the first time showed that reef and/or bank‐edge facies were present. In addition, more than 200 oil seeps were known in a linear zone along the foot of the Sierra de Chiapas, south of and adjacent to the coastal plain. If one assumes a facies distribution similar to that of the Golden Lane, it can be concluded that an extensive bank‐edge talus deposit should lie gulfward from the lagoonal facies. With this geologic concept in mind, seismic work was commenced, and drilling during 1971–1972 led to the dual discoveries of the Sition Grande and Cactus oil fields in 1972. The first offshore discovery, Chac, was made in 1976.The Great Carbonate Bank of Yucatán is believed to include not just the Yucatán Peninsula, but also a part of coastal Veracruz State, where several discoveries have been made in carbonate rocks of Early‐ to Middle‐Cretaceous ages in thrust sheets along the western margin of the Veracruz basin, which are now buried beneath the coastal plain. It is probable that large, subthrust, anticlinal structures underlie the thrust sheets along the western margin of the Veracruz basin. These, when drilled, ma

ISSN:0141-6421    

DOI:10.1111/j.1747-5457.1981.tb00930.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

The impact cratering process results in unique structures and extensive fracturing and brecciation of the target rock which can be conducive to hydrocarbon accumulations. Examination of Viewfield and Red Wing Creek oil pools in North America reveals that they may have been formed by meteoritic impact in Paleozoic sediments. Additional hydrocarbon traps have most likely been produced by impact but have not been recognized as such because geologists are generally not familiar with crater structures and shock‐metamorphic effects in rocks. It is proposed that petroliferous basement impact craters also exist and that despite arguments to the contrary, at least one may have already been found. Further discoveries are severely limited because of conservative exploration procedures, which characteristically avoid penetrating crystalline basement.Core analysis from several large impact sites developed in crystalline rocks reveals that while permeability factors are marginal, the reservoir potential of these craters exceeds those of many of the largest known hydrocarbon accumulations. Preservation age studies of craters in conjunction with size frequency distribution curves implies that many will have been buried before erosional eradication. As with normally‐fractured and brecciated basement areas, some will have accumulated hydrocarbons. In addition to classical source rocks flanking or overlying these potential reservoirs, recycled kerogen and the possibility of inorganic sources are also considered. A basement impact crater may afford a unique way of testing the inorganic hydrocarbon propos

ISSN:0141-6421    

DOI:10.1111/j.1747-5457.1981.tb00931.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

The history of petroleum exploration in Lebanon and the known stratigraphic succession and structural evolution are briefly reviewed. The negative results of the six relatively‐deep exploration boreholes so far drilled cannot be regarded as condemning the petroleum potential of Lebanon, in view of the fact that none explored formations older than the earliest exposed (Lower Jurassic) nor the offshore, and particularly in view of the many hydrocarbon indications encountered, especially when the earlier and recent geochemical work results on source rock potential and origin of shows are considered. Correlation with updated surface and subsurface data from Syria and Jordan enhance the probability of favourable seal formation development in the Late Triassic under Lebanon while favourable location for source/reservoir rock facies emerges when the palaeogeography is considered; postulated Palaeozoic facies also offer favourable potential. The effects of limited extrusive phases in the Late Jurassic/Early Cretaceous and the Late Neogene are examined and considered as non‐critical to hydrocarbon accumulation other than on a very limited local structure scale, while the structural effects of Neogene horizontal displacements along the length of the country are taken into account in the presentation of three exploration options designed to look thoroughly at pre‐Jurassic pros

ISSN:0141-6421    

DOI:10.1111/j.1747-5457.1981.tb00932.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

Anomolous seismic horizons which (1) are strongly reflective, i.e. have a high impedence contrast; (2)cut across bedding planes of sediments;(3)are subparallel with the sea floor; and (4)increase their sub‐bottom depth with increasing depth of sea floor (and thus with decreasing temperature of bottom water) are tentavely identifed as the base of a gas hydrate layer. The anamalous reflections occur below waters 1000‐2500m deep, and along 500km of the continental slope. Some 10–20,000 sq km appear to be underlain by gas hydrates.The hydrate layer is often associated with structural anomalies(anticlines, tilted faultblocks). These would allow gas to migrate up‐dip into pressure and temperature conditions suitable for hydrate formation. Since the hydrate‐cemented layer itself acts as a barrier to gas migration, free gas will be trapped and accumulated in the sediments beneath it.It is concluded that huge amounts of hydrocarbon gas, both free gas and solid hydrate, have accumulated in this continental margin. On land, gas and oil generation is widespread, mainly originating from overpressured, Lower Teritiary to Upper Cretaceous shales. From seismic evidence the same formations appear to extend under the shelf and continental slope. The extensive occurence of gas hydrates would confirm that organicrich, terrigenous sediments have extensively been deposited in th

ISSN:0141-6421    

DOI:10.1111/j.1747-5457.1981.tb00933.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

Difficulty of migrating a large amount of oil in either molecular or micellar solution may lead to an assumption that a continous oil phase or a relatively high (20–30%) concentration of oil in pores of shales is necessary for primary migration to overcome the capillary restrictions against the oil. Movement of small oil globules in shales is believed by many workers to be an extremely difficult process. However, the above assumption is not necessarilly valid in shales which contain a large quantity of structured and semi‐solid water. Such oil globules may defrom by the effect of compacting grains (solid material) and the semi‐solid water, thus reducing the capillary restrictions significantly. This suggests that the small oil globules which are separated from each other can move in the direction of lower stress in the shales: a continous oil phase or relatively high oil concentration is not a necessary requirement for primary oil migr

ISSN:0141-6421    

DOI:10.1111/j.1747-5457.1981.tb00934.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

This paper comprises a continuation of the second section of a detailed and riegorous geomechenical analysis of the stability of overpressured, gently‐sloping sediment layers presented in the Journal of Petroleum Geology 2, 3, 1980 and 3,2, 1980. The authors continue to describe the delta model which they use to explain and permit quantitative reproduction of the main features associated with growth faulting; part II(a) considered stress equilibrium, related stress equations, types of overpressure, the representation of the stress state in Mohr space and the plastic/elastic stated of frictional materials in long, fluid‐filled layers. The present article continues with the analysis, with a numerical and analytical examination of slip lines and considerations of plastic, flow and slip.Peak‐strenght phenomena and the effect of purely‐cohesive materials on the theory conclcude the paper in our next issue, together with a discussion of the behaviour of watersaturated soils(as opposed to theoretical solid material with elastic and plastic properties), and the six major conclusions which can be drawn from t

ISSN:0141-6421    

DOI:10.1111/j.1747-5457.1981.tb00935.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

ISSN:0141-6421    

DOI:10.1111/j.1747-5457.1981.tb00936.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

ISSN:0141-6421    

DOI:10.1111/j.1747-5457.1981.tb00937.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY