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Jurassic High-resolution Sequence Stratigraphy And Oil/gas Potential In Qiangtang Basin

Posted on:2005-08-27Degree:DoctorType:Dissertation
Country:ChinaCandidate:Z Q ShiFull Text:PDF
GTID:1100360122992929Subject:Mineral prospecting and exploration
Abstract/Summary:PDF Full Text Request
High-resolution sequence stratigraphy has been extensively applied to oil/gas exploration due to its bran-new theory, methods and high accuracy and predictability. It was introduced into China during the 1990s and then was widely used in the study of continental petroliferous basins and continental deposits. However, the applications of high-resolution sequence stratigraphy have been seldom reported on the marine depoits, especially the marine carbonate sediments in China. The paper for the first time applies the theory to the study of Jurassic sequence stratigraphy in Qiangtang Basin, Tibet, which was expected to reveal the practicality of the theory on the marine deposits containing both clastic rocks and carbonate rocks.Based on the theory of high-resolution sequence stratigraly, 3 super-long-term cycle sequences are identified from the Jurassic sediments in Qiangtang Basin, amony which 2 developes from middle-upper Jarassic. 7 long-term, 17 middle-term cycle sequences are distinguished from the 2 middle-upper Jurassic super-long-term cycle sequences. The systemic analysis of Jurassic outcrops shows that the interfaces of long-term cycle sequences are CD the scoured bases of coastal onlap and fluvial/tidel channels, which usually distribute at the marginal region of Qiangtang Basin and lie to the base of sandstone or conglomerate sediments, (2) the widely distributed base interfaces of supratidal or evaporitic lagoonal gypsum depoits, which implies the most falling of long-term cycle face, (3) the base interfaces of supratidal mudstones and breccia, which implies the sedimentary discontinuities, (4) palaeosoil and palaeocalcrete occurring in the dolostone, (5) conformable interfaces occurring in the area with relatively deep water. Three basic types of short-time cycle sequence are identified in this paper. Accurate high-resolution equitime correlation is made and sequence framework is established. The study shows that high-resolution sequence stratigraphy can be applied well to marine clastic even carbonate deposits and do well to the forcast and correlation of the combination of oil/gas source beds, reservoirs and cap formations.According to the sedimentological evidences the paper believes that Qiangtang Basin was a continental marginal basin during middle Jurassic time and was at an extensional architectonic setting. A series of garbens and horsts developed during the earliest period of middle Jurassic time and conglomerates deposited along the synsedimentary normal faults occurring at the margin of the garbens. Due to the study of upper-Jurassic Xweshan formation, it is also believed that sediments deposited with a compressional geotectonic setting during late Jurassic time. The palaeosea water exited northwestward and sowtheastward.Using the data of equitime correlation of base cycles, petrographical analysis, the Jurassicevolution of facies palaeogeography is revealed in this paper. During the MSC1 (when the first middle-term cycle developed), MSC2 and MSC3 period, the paleotopography varied and fan-deltas developed in Qiangtang Basin. During the MSC4 and MSC5 period, clastic rocks of tidel-flat facies and shore-shallow sea facies mainly deposited. Carbonate platform depositional system developed during the MSC6, MSC7 and MSC8 period and it was closely related to the rise of global sea level during the Bathonian period. During the MSC9 and MSC 10 period shore-shallow sea, tidel-flat and delta facies clastic rocks deposited. The MSC11, MSC12 and MSC 13 middle-term cycles developed during the later Jurassic Oxford and Kimerry period and mixed continental shelf sediment developed. During the MSC 14, MSC 15 and MSC 16 period the water of Jurassic Qiangtang sea exited from the researched region and the area of continental deposits extanded.With the high-resolution sequence stratigraphical analysis, data of outcrop formations, charaters and combination of oil/gas source rocks, reservoirs and cap rocks, oil/gas shows, tectonic conditions and the matched relation between oil/gas generating peak and sour...
Keywords/Search Tags:Qiangtang Basin, High-resolution Sequence Stratigraphy, Jurassic, Tibetan Plateau, Sedimentary facies
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