Major factors affecting the closure of marine carbonate caprock and their quantitative evaluation: A case study of Ordovician rocks on the northern slope of the Tazhong uplift in the Tarim Basin, western China
Lu X.,China University of Petroleum - Beijing |
Wang Y.,China University of Petroleum - Beijing |
Yu H.,Petrochina |
Bai Z.,Oil and Gas Survey
Marine and Petroleum Geology | Year: 2017
There are many examples of oil and gas reservoirs throughout the world that have tight carbonate rock as the caprock. These oil and gas reservoirs are often vertically overlapped (with multiple oil and gas sections) and laterally connected (to many oil and gas reservoirs). The closure of carbonate caprock is affected by many factors, such as the clay content, differential diagenesis and layer thickness. As evaluation parameters, the clay content can be determined by a gamma ray well-logging curve; the differential diagenesis is reflected in filling effects, rupture effects, cement composition and content and can be measured through the displacement pressure; the layer thickness can be obtained from drilling and well-logging data. In different regions or different members, the factors and parameters to be considered or evaluated for the closure are dependent on actual geological conditions. In this study, the clay content, displacement pressure and layer thickness were analysed, determined, calculated and normalized to generate an overall closure evaluation index (λ) for the caprock in wells on Ordovician Liang 3–5 mud-bearing limestone members on the northern slope of the Tazhong uplift. On the plane distribution map, the area with λ ≥ 1 was effectively sealed. The tight carbonate in the inner Yingshan Formation (with high-resistivity, referred to as a high-resistivity layer) was also effectively caprock. Regardless of whether it can seal oil and gas, the sealing capacity mainly depends on the displacement pressure difference between the high-resistivity layer and the underlying carbonate reservoir. Based on drilling results and the comparison of the displacement pressure difference between the two layers (by actual measurements and calculations), we observed that when the pressure difference is more than 1.95 MPa, it is an effective caprock. © 2017 Elsevier Ltd
Li B.,Chinese Academy of Geological Sciences |
Ji J.,Peking University |
Wang D.,Oil and Gas Survey |
Gong J.,Peking University |
Ma Z.,Peking University
International Geology Review | Year: 2014
The Ailao Shan-Red River (ASRR) shear zone, a long, narrow metamorphic belt that strikes NW-SE, is the continuation of the southeastern margin of the Tibetan Plateau. It mainly comprises amphibolite-facies mylonitic gneiss. In this study, we report zircon concordant U-Pb SHRIMP ages of 37.52 Ma ± 0.67 Ma [mean square weighted deviation (MSWD) = 1.4] and 30.8 Ma ± 0.3 Ma (MSWD = 3.2) from a granitic gneiss in the northern part of the Ailao Shan metamorphic belt, and from a leucogranitic dike in the middle of the zone, respectively. Zircon U-Pb ages between 35 Ma and 41 Ma were also obtained from a biotite gneissic granite in the southern part of the belt. Contrasting the internal structure of the zircon crystals with our new U-Pb dating suggests that their nucleation and growth initiated during a late Eocene tectonic uplift event between ca. 40 and 35 Ma. Detailed field observations and zircon U-Pb dating results suggest that the deformation time of mylonitic gneiss and granitic gneiss in the ASRR was 40-30 Ma, the formation age of the gneissic schistosity of the ASRR metamorphic belt was as early as ca. 40 Ma. © 2014 © Taylor & Francis.
Shi L.,China University of Petroleum - Beijing |
Jin Z.,China University of Petroleum - Beijing |
Yan W.,China University of Petroleum - Beijing |
Li G.,China University of Petroleum - Beijing |
And 2 more authors.
Zhongguo Kuangye Daxue Xuebao/Journal of China University of Mining and Technology | Year: 2015
Based on data from thin section analysis, core analysis, particle analysis, and SEM, this paper studies the influence mechanism of abnormal high pressure on dissolution and diagenetic stage in northwestern Bozhong sag. A new mechanism of reservoir dissolution was found. The particles dissolution was prior to occur in the specific grain size of sandstone under different reservoir pressures. The new mechanism reveals that reservoir dissolution will be promoted by abnormal high pressure. The dissolution strength changes very little and the envelope curve represents the gentle slope shape as depth decreases from abnormal pressure regions to the normal pressure regions. The new mechanism provides compelling evidence for inhibition of organic maturation and clay mineral transformation due to abnormal high pressure. The results show that particles dissolution is prior to develop in sandstone with coarser grain size in abnormal high pressure regions, where average added rate of secondary pore is about 32.0%, Ro is near 0.56% in the depth from 3 200 m to 3 300 m and the mass fraction of montmorillonite in mixed-layer is 20%. The sandstone with finer grain size has priority to form particle dissolution in normal pressure regions deeper than 2 950 m. The average added rate of secondary pore is approximate 34.2%, Ro is about 0.58% and the mass fraction of montmorillonite is about 14.6%. However, the particle dissolution has no obvious correlation with particle grain size in the normal pressure regions below 2 950 m. And the average added rate of secondary pore is about 26.5%. The developing depth of reservoir dissolution is over 430 m in normal pressure regions next to the abnormal high pressure regions. The influence model of abnormal high pressure on reservoir dissolution is summarized. Combined with the newly found dissolution mechanism, the hydrocarbon exploration in search of secondary pore zone can be guided. ©, 2015, China University of Mining and Technology. All right reserved.
Huang Y.,China University of Geosciences |
Yang G.,Beijing University of Technology |
Gu J.,China University of Geosciences |
Wang P.,Oil and Gas Survey |
And 3 more authors.
Palaeogeography, Palaeoclimatology, Palaeoecology | Year: 2013
Songliao Basin in NE China developed the most productive oilfield in the world sourced from terrestrial rocks. The main source rock of the basin includes member 1 of the Qingshankou (K2qn1) and members 1 and 2 of the Nenjiang Formation (K2nj1-2). However the exact reasons for the formation of the source rock, especially the K2qn1 are still controversial. Former paleontological and organic geochemical research suggested that organic matter was deposited during marine incursion events of K2qn1 but further geochemical evidence is needed. This paper explores the distinct sulfate levels that distinguish marine from fresh waters of the Songliao paleo-lake. We undertook a systematic investigation the sulfur geochemistry of the sediments from top of member 4 of the Quantou Formation (K1q4) to top of member 1 of the Qingshankou (K2qn1). The ratio of organic carbon to the pyrite sulfur (TOC/PYS) proved the previously suggested saline conditions during the deposition of K2qn1; and the pyrite sulfur isotope indicated that marine incursion may not only have occurred for K2qn1, but also for top of K1q4. The exact time for the beginning of marine incursion is to be determined. The marine incursion within K2qn1 is not strong and partially controlled by the fluctuation of paleo-lake level. The present study will be helpful for understanding the contribution of marine incursion events to the burial of organic carbon in the Songliao paleo-lake, although further studies are still needed. © 2013 Elsevier B.V.
Ge X.-H.,Jilin University |
Ge X.-H.,China University of Geosciences |
Liu J.-L.,China University of Geosciences |
Ren S.-M.,Oil and Gas Survey |
Yuan S.-H.,Institute of Disaster Prevention
Geology in China | Year: 2014
In the Wilson cycle proposed in the 1960s, the collision of tectonic plates which leads to closure of oceanic basins on both sides of plates marks the end of the cycle. In interpreting continental tectonics in the past 20 years, it seems that the above conclusion is not comprehensive. Diffusive and widely distributed intracontinental deformation suggests that the action of plate collision has not ceased. After the formation of the Paleo-Asian continent, tectonic deformation, magmatism and cratonic basin formation widely developed during Mesozoic-Cenozoic period in eastern China were possibly related to the progressive opening of the Indian Ocean and the Arctic Ocean as well as the subduction of the Western Pacific and Philippine oceanic plates. This paper intends to discuss the major tectonic events, structural properties, the formation background and the temporal and spatial distribution of Mesozoic-Cenozoic tectonics in eastern China. From Late Hercynian to Indosinian period, the Paleo-Asian continent was formed due to amalgamation of various tectonic blocks during the closure of the Paleo-Tethys. During Late Jurassic - Early Cretaceous, accompanied by the closure of the Mongo-Okhotsk ocean, the continent-continent collision gave rise to the formation of the Paleo-Asian continent. Thrust-nappe structures were formed during the intracontinental deformation. At the same time, the Western Pacific Isanagi plate was subducted obliquely, which caused superimposation effect from east to west. In the Middle-Late Cretaceous-Paleogene period, together with the transition from thickened crust to lithospheric thinning and transformation, the intracontinental extensional deformation approached its peak stage. Continental craton basins peneplanes were formed. From Late Eocene to early Miocene (40-23 Ma), the superposition of the motion of the Pacific plate turning in NWW direction, the spreading of the middle oceanic ridges of the Indian Ocean, and the continent-continent collision between the Indian-Australian and the southern part of the paleo-Asian plate induced the formation of the new tectonic landforms in eastern China. Affected by East Asia-Western Pacific rift and the Indian Ocean ridge spreading during Middle Pliocene and early Pleistocene, the eastern China continent experienced lithospheric mantle uplift, crustal thinning, marginal and intracontinental extensional deformation. These processes resulted in the successive formation of marginal seas, island arc, rift basins and eroded highland landscapes. During Early Pleistocene (0.9-0.8 Ma) - Late Pleistocene (0.01 Ma) period, the tectonic landforms of Eastern China were finally formed.
Lu Z.,Oil and Gas Survey |
Lu Z.,Chinese Academy of Geological Sciences |
Xue X.,Chinese Academy of Geological Sciences |
Liao Z.,CAS Guangzhou Institute of Geochemistry |
Liu H.,Oil and Gas Survey
Energy and Fuels | Year: 2013
The composition and isotope ratio of gases from gas hydrate and organic geochemistry of mudstone, oil shale, and coal within a gas hydrate-bearing interval in the Qilian Mountain permafrost suggest that gases from gas hydrate are derived from the deep, but the lithology and burial depth of source rocks for gases from gas hydrate are not yet known. In this study, samples of mudstone, oil shale, and coal were analyzed with thermal stimulation within the gas hydrate-bearing interval in the Qilian Mountain permafrost. Results showed that gas composition and carbon isotopes of hydrocarbon gases thermally stimulated from mudstone at temperatures of 350-400 C and from oil shale at temperatures of 380-400 C are similar to those of gases from gas hydrate, indicating that the deep mudstone and oil shale are potential source rocks for gases from gas hydrate. The gas composition of hydrocarbon gases thermally stimulated from coal was similar to that of gas hydrate, but their carbon isotope values were very different, suggesting that coal was not necessarily related to a gas source for gas hydrate. The burial depths of source rocks for gases from gas hydrate were further estimated to be 1500-2000 m on the basis of the relationship among thermally stimulated temperature, vitrinite reflectance, and burial depth in the study area. © 2013 American Chemical Society.
Han L.,Beijing University of Chemical Technology |
Han L.,East China Normal University |
Wu S.-J.,Beijing University of Chemical Technology |
Qin C.-Y.,Beijing University of Chemical Technology |
And 4 more authors.
Antonie van Leeuwenhoek, International Journal of General and Molecular Microbiology | Year: 2014
A red-pink, Gram-negative, rod-shaped, non-motile, non-spore-forming bacterium, designated strain DK6-37 was isolated from the permafrost region of Qilian Mountains in northwest of China. Phylogenetic analysis based on 16S rRNA gene sequencing indicated that this isolate represents a novel member of the genus Hymenobacter, with low sequence similarities (<97 %) to recognized Hymenobacter species. Optimum growth was observed at 28°C, pH 7.0 and 0 % NaCl. The strain was found to contain MK-7 as the predominant menaquinone. The polar lipids were identified as phosphatidylethanolanmine, two unknown aminophospholipids, one unknown aminolipid and three unknown polar lipids. The major fatty acids were identified as summed feature 3 (C16:1 ω7c/C16:1 ω6c as defined by MIDI), summed feature 4 (anteiso-C17:1 B/iso-C17:1 I), C16:1 ω5c, iso-C17:0 3-OH, iso-C15:0 and C18:0. The DNA G + C content was determined to be 67.4 mol %. On the basis of the polyphasic evidence presented, it is proposed that strain DK6-37 represents a novel species of the genus Hymenobacter, for which the name Hymenobacter qilianensis sp. nov. is proposed. The type strain is DK6-37T (= CGMCC 1.12720T = JCM 19763T). © 2014 Springer International Publishing.
Zhang R.-G.,Beijing University of Chemical Technology |
Tan X.,Beijing University of Chemical Technology |
Zhao X.-M.,Oil and Gas Survey |
Deng J.,Oil and Gas Survey |
Lv J.,Beijing University of Chemical Technology
International Journal of Systematic and Evolutionary Microbiology | Year: 2014
A Gram-reaction-negative, yellow-pigmented, strictly aerobic bacterium, designated M0116T, was isolated from the sediment of the Mohe Basin in north-east China. Flexirubin-type pigments were produced. Cells were catalase- and oxidase-positive and non-gliding rods. Phylogenetic analysis based on 16S rRNA gene sequences revealed that strain M0116T was a member of the family Flavobacteriaceae and was most closely related to members of the genera Empedobacter, Wautersiella and Weeksella with 90.5-91.0% sequence similarities. The major cellular fatty acids were iso-C15: 0 and iso-C17: 0 3-OH. The major respiratory quinone was MK-6 and the major polar lipid was phosphatidylethanolamine. The DNA G+C content was 38.2 mol%. Based on phenotypic, phylogenetic and genotypic data, strain M0116T is considered to represent a novel species of a new genus in the family Flavobacteriaceae, for which the name Moheibacter sediminis gen. nov., sp. nov. is proposed. The type strain is M0116T (5CGMCC 1.12708T=JCM 19634T). Emended descriptions of Empedobacter brevis, Wautersiella falsenii and Weeksella virosa are also proposed. © 2014 IUMS.
Wang P.,Oil and Gas Survey |
Wang P.,Chinese Academy of Geological Sciences |
Zhu Y.,Oil and Gas Survey |
Lu Z.,Oil and Gas Survey |
And 3 more authors.
Cold Regions Science and Technology | Year: 2014
Fracture-filling pyrites, which semi-filled or fully filled rock fractures, were commonly found in the cores from all hydrate testing well in the Qilian mountain permafrost. The occurrence of the pyrites is very similar to the "fracture-filling" gas hydrate that occurred in this area, and whose distribution mainly concentrated below the hydrate layer or layer of hydrate associated anomaly. This paper carried out the study in morphology and sulfur isotope for the fracture-filling pyrites. The results show that fracture-filling pyrites consisted of cube form pyrite crystals, directionally spread in a step-like fashion along the fracture surface, and associated with a circular structure; the value of δ34SCDT ranges from 6.761‰ to 41.846‰, and the most positive excursion exists below the deepest layer of hydrate associated anomaly. The characters in pyrite crystal morphology, sulfur isotopic composition and spatial distribution closely related with the secondary change of metastable gas hydrate reservoir. The permafrost degeneration resulting from climate warming is the most direct cause for gas hydrate stability zone (GHSZ) migration that occurred in the Qilian mountain. The zone between the shallowest and the deepest distribution of the fracture-filling pyrite recorded the possible largest original GHSZ. The top and the bottom of GHSZ have moved downward and upward to a certain extent, respectively, further inferring that the depth of permafrost has decreased about 10 m in the boreholes. © 2013 Elsevier B.V.
Lu Z.,Chinese Academy of Geological Sciences |
Zhu Y.,Chinese Academy of Geological Sciences |
Liu H.,Chinese Academy of Geological Sciences |
Zhang Y.,Chinese Academy of Geological Sciences |
And 3 more authors.
Marine and Petroleum Geology | Year: 2013
Gas source for gas hydrate is not clear yet in the Muli of Qilian Mountain permafrost. In this paper a case is illustrated in the hole of DK-2 during gas hydrate drilling; gas composition and isotopes of gas hydrate and its associated gases are analyzed; organic geochemistry on mudstone, oily shale, coal, oil & gas indications are correlated within the interval of gas hydrate occurrences; the aim is to discuss the source of gases from gas hydrate and its implication to gas hydrate exploration in the study area. Results from gas composition and isotopes of gas hydrate and its associated gases reveal that the origin of gases from gas hydrate is mainly concomitant with deep oil or crude oil in the study area. Parameters for the abundance, type and thermal evolution of organic matter in mudstone, oil shale, coal in the same interval of gas hydrate occurrence suggest that these strata, especially within gas hydrate stability zone, play little role in gas sources for gas hydrate. Reservoir pyrolysis results for oil & gas indication-bearing cores reveal that oil & gas indications are closely associated with gas hydrate within its interval, indicating that they may serve as a sign of gas hydrate in the study area. © 2013 Elsevier Ltd.