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71.
渝东武隆上寒武统地层,储集空间以次生孔隙为主,包括晶间孔、晶间溶孔、粒内溶孔、粒间溶孔、铸模孔、溶洞、裂缝。成岩作用是影响储集性能的主要因素。研究区成岩作用,依据其对孔缝的影响,以及本组地层特征可分为建设性成岩作用和破坏性成岩作用两种类型,前者包括白云石化作用、溶蚀作用、破裂作用;后者包括胶结作用、压实压溶作用、充填作用。 相似文献
72.
73.
Norbert R. Nowaczyk Stefanie Harwart Martin Melles 《Geophysical Journal International》2001,145(1):300-306
74.
Plagioclase dissolution related to biodegradation of oil in Brent Group sandstones (Middle Jurassic) of Gullfaks Field, northern North Sea 总被引:1,自引:0,他引:1
Brent Group sandstones from the north side of the Gullfaks Oilfield contain mostly 5–8% albitic plagioclase, whereas plagioclase is almost absent in the same strata in the southern part of the field. Absence of plagioclase throughout the entire vertical extent of the Brent Group in the southern wells seems to rule out provenance as the principal explanation for differing plagioclase content, which is therefore interpreted as the result of diagenesis. Hypotheses for the nature of the inferred leaching event include epigenetic meteoric diagenesis and mesogenetic release of acid components from clay minerals or kerogen, but these explanations are unable to account for the observed spatial distribution of the plagioclase-bearing and plagioclase-free sandstone intervals. However, overall correspondence between the area lacking plagioclase and oil compositions having both anomalously high CO2 and organic geochemical indications of advanced biodegradation suggest a link between plagioclase dissolution and biodegradation of the present oil column. It is, therefore, proposed that acid components from biodegradation selectively reacted with albitic plagioclase to form kaolin, releasing sodium bicarbonate into the residual water. The plagioclase-free sandstones contain more kaolin than the plagioclase-bearing sandstones, as would be expected due to aluminium conservation. However, the wide and overlapping ranges of kaolin content in both groups suggest that most of the kaolin originated from processes other than biodegradation-driven plagioclase alteration, potentially including both epigenetic and mesogenetic dissolution, as well as deposition of detrital kaolin and kaolin precursors. 相似文献
75.
Cryptic sequence boundaries in braided fluvial successions 总被引:2,自引:0,他引:2
In braided fluvial deposits, consisting of monotonous successions of sandstone or conglomerate, it may be difficult to distinguish regionally significant bounding surfaces (sequence boundaries) from autogenic channel-scour surfaces. Major surfaces may be characterized by erosional relief and draped by lag deposits, but not all sequence boundaries show these characteristics. Other clues to the presence of a major surface are sharp changes in detrital composition, shifts in regional palaeocurrent trends and evidence of early diagenesis of the sandstones immediately below the sequence boundary. Examples of these attributes of cryptic sequence boundaries are illustrated from three Mesozoic units in the Colorado Plateau area of the United States. In the Chinle Formation (Triassic), near Moab, Utah, angular intraformational unconformities overlie sandstones showing evidence of early diagenesis. In the Castlegate Sandstone (Upper Cretaceous) of east-central Utah, a cryptic sequence boundary can be discriminated from other erosion surfaces by the evidence of detrital petrography and early diagenesis. Palaeocurrent data indicate changes in regional palaeoslope at two sequence boundaries within this unit. Evidence of early diagenesis is also present at a sequence boundary in the Kayenta Formation (Jurassic) of westernmost Colorado. 相似文献
76.
77.
78.
鄂尔多斯盆地下奥陶统白云岩成因类型及其地球化学特征 总被引:5,自引:0,他引:5
鄂尔多斯盆地天然气藏的主要储集层段,下奥陶统白云岩,按成因可分为准同生、成岩和深埋藏三种类型,它们在岩石结构、X射线衍射、阴极发光、稳定同位素、微量元素特征以及白云石化机理上均有较大差别。 相似文献
79.
Hans G. Machel 《Hydrogeology Journal》1999,7(1):94-107
This article provides a critical synopsis of the effects of groundwater flow on mineral diagenesis. Emphasis is placed on
those aspects and processes that change porosity and permeability in carbonate aquifers, because they are of particular importance
to human societies as sources of supplies of water for human consumption (drinking, irrigation) and of crude oil and natural
gas.
Diagenetic settings in carbonates as well as clastics are generally ill defined. This paper proposes a new comprehensive classification
of diagenetic settings into near-surface, shallow-, intermediate-, and deep-burial diagenetic settings; hydrocarbon-contaminated
plumes; and fractures. These settings are defined on the basis of mineralogy, petroleum, hydrogeochemistry, and hydrogeology.
This classification is applicable to all sedimentary basins.
Diagenesis is governed by various intrinsic and extrinsic factors that include thermodynamic and kinetic constraints, as well
as microstructural factors that may override the others. These factors govern diagenetic processes, such as dissolution, compaction,
recrystallization, replacement, and sulfate–hydrocarbon redox-reactions. Processes such as cementation, dissolution, and dolomitization
require significant flow of groundwater driven by an externally imposed hydraulic gradient. Other processes, such as stylolitization
and thermochemical sulfate reduction, commonly take place without significant groundwater flow in hydrologically nearly or
completely stagnant systems that are geochemically "closed."
Two major effects of groundwater flow on mineral diagenesis are enhancement and reduction of porosity and permeability, although
groundwater flow can also leave these rock properties essentially unchanged. In extreme cases, an aquifer or hydrocarbon reservoir
rock can have highly enhanced porosity and permeability due to extensive mineral dissolution, or it can be plugged up due
to extensive mineral precipitation.
Received, April 1998 · Revised, July 1998 · Accepted, September 1998 相似文献
80.
Laboratory simulation of the catagenesis of organic matter in sedimentary rocks has been used to provide an understanding of the processes involved in petroleum generation. Several of these studies have focused on the thermal evolution of organic matter (OM) present in Recent sediments. This study examines the geochemical characteristics and experimental thermal evolution of primary organic matter from two organic facies that are thought to be major contributors to Venezuelan hydrocarbon source rocks. A third facies, generally considered unimportant for petroleum formation, is used to contrast the experimental results. Hydrous pyrolysis maturation experiments were performed for three intermediate temperatures. The products of the final 330°C stage are shown in this paper because they best illustrate the changes in the OM during catagenesis. Results from the hydrous pyrolysis experiments show that at 280°C and higher all three samples yield liquid hydrocarbons similar in composition to natural crudes and the transformed organic matter is similar to kerogen that occurs in natural source rocks. Chromatograms from the saturated fraction of extracts at 330°C are similar to natural crudes with respect to n-alkane distribution and abundance of beta; and beta;alpha; hopanes. The only difference seems to be the relative abundance of 22R over 22S isomers, which indicates immature oil. This is in contrast to indications from the R
o and T
max parameters measured on the accompanying kerogen. 相似文献