Geological roles of the siltstones in tight oil play     

《Marine and Petroleum Geology》2017

Understanding the hydrocarbon accumulation pattern in unconventional tight reservoirs is crucial for hydrocarbon evaluation and oil/gas extraction from such reservoirs. Previous studies on tight oil accumulation are mostly concerned with self-generation or from source to reservoir rock over short distances. However, the Lucaogou tight oil in Jimusar Sag of Junggar Basin shows transitional feature in between. The Lucaogou Formation comprises fine-grain sedimentary rocks characterized by thin laminations and frequently alternating beds. The Lucaogou tight silt/fine sandstones are poorly sorted. Dissolved pores are the primary pore spaces, with average porosity of 9.20%. Although the TOC of most silt/fine sandstones after Soxhlet extraction is lower than that before extraction, they show that the Lucaogou siltstones in the area of study have fair to good hydrocarbon generation potential (average TOC of 1.19%, average S₂ of 4.33 mg/g), while fine sandstones are relatively weak in terms of hydrocarbon generation (average TOC of 0.4%, average S₂ of 0.78 mg/g). The hydrocarbon generation amount of siltstones, which was calculated according to basin modeling transformation ratio combined with original TOC based on source rock parameters, occupies 16%–72% of oil retention amount. Although siltstones cannot produce the entire oil reserve, they certainly provide part of them. Grain size is negatively correlated with organic matter content in the Lucaogou silt/fine sandstones. Fine grain sediments are characterized by lower deposition rate, stronger adsorption capacity and oxidation resistance, which are favorable for formation of high quality source rocks. Low energy depositional environment is the primary reason for the formation of siltstones containing organic matter. Positive correlation between organic matter content and clay content in Lucaogou siltstones supports this view point. Lucaogou siltstones appear to be effective reservoir rocks due to there relatively high porosity, and also act as source rocks due to the fair to good hydrocarbon generation capability.  相似文献   

Hydrocarbon source potential of Eocene-Miocene sequence of Western Sabah,Malaysia     

《Marine and Petroleum Geology》2017

An evaluation of the petroleum generating potential of onshore Eocene-Miocene sequences of Western Sabah, Malaysia was performed based on organic petrological and geochemical methods. The sequences analysed are the Belait, Meligan, Temburong and West Crocker formations of western Sabah. The Belait Formation which is Stage IV equivalent in the offshore represents one of the major source rock/reservoirs of the petroleum-bearing Sabah Basin. The Eocene-Early Miocene West Crocker and Temburong formations are deepwater turbidites whilst the Miocene Meligan and Belait formations are shallow marine fluvio-deltaic deposits. The vitrinite reflectance and pyrolysis T_max values show that the Belait samples are generally immature for hydrocarbon generation, whereas the Meligan, Temburong and West Crocker samples are in the mature to late maturity stage of hydrocarbon generation. The overall bulk source rock properties of the Belait and Meligan show fair to good petroleum source rock potential with TOC more than 1 wt %, hydrocarbon yield in the range of 400–1300 ppm and moderately high HI for many of the samples. Most of the samples representing the Temburong and West Crocker formations have TOC less than 1 wt% and have no to fair hydrocarbon generating potential. Interestingly, the samples collected in the West Crocker Formation characterized by slump deposits (MTD) have TOC>2 and possess good to excellent hydrocarbon generating potential. The organic matter present in all of the studied formations is mainly of terrigenous origin based on the abundance of woody plant materials observed under the microscope. Consequently, the analysed sequences are predominantly gas prone, dominated by Type III and Type III-IV kerogen except for minor occurrence of mixed oil-gas prone Type II-III kerogen in the Belait Formation and in the slump mass transport deposits (MTD) of the West Crocker Formation.  相似文献   

Diversified roles of mineral transformation in controlling hydrocarbon generation process,mechanism,and pattern     

Jiazong Du  Jingong Cai  Tianzhu Lei  Yingli Li 《地学前缘(英文版)》2021,12(2):725-736

Organic matter(OM)is intimately associated with minerals in clay-rich mudstones,leading to widespread organic-mineral interaction during hydrocarbon generation in argillaceous source rocks.What we are concerned is the effects of the different mineral properties on hydrocarbon generation process and mechanism during mineral transformation.In this way,pyrolysis experiments with smectite-octadecanoic acid complexes(Sm-OA and Ex-Sm-OA)were conducted to analyze correlation of mineralogy and pyrolysis behaviors.Based on organicmineral interaction,hydrocarbon generation process was divided into three phases.At 200–300℃,collapse of smectite led to desorption of OM,resulting in high yield of resin and slight increase in saturates.Subsequently,enhanced smectite illitization at 350–450
℃was accompanied with large amounts of saturates and a mere gaseous hydrocarbon.Featured by neoformed plagioclase,ankerite,and illite,500
C saw plenty of asphaltene and methane-rich gaseous hydrocarbons,revealing cracking reactions of OM.Noteworthy is that saturated and gaseous hydrocarbons in Ex-Sm-OA were considerably more than that in Sm-OA during second and third phases.Quantitative calculation of hydrogen revealed organic hydrogen provided by cross-linking of OM could not balance hydrogen consumed by cracking reactions,but supply of inorganic hydrogen ensured cracking could readily occur and consequently greatly promoted hydrocarbon generation.Further investigating characteristics of mineralogy and pyrolytic products,as well as effects of solid acidity on hydrocarbon generation,we concluded desorption of OM and decarboxylation promoted by Lewis acid were dominated at 200–300
C,resulting in lowdegree hydrocarbon generation.While high yield of saturated and gaseous hydrocarbons in second and third phases,together with occurrence of ankerite,indicated predominance of decarboxylation and hydrogenation promoted by Lewis and Br?nsted acid,respectively.Variations in organic-mineral interactions indicated(1)the controls of mineral transformation on hydrocarbon generation process and mechanism include desorption,decarboxylation,and hydrogenation reactions;(2)clay minerals acted as reactants evolving together with OM rather than catalysts.These findings are profoundly significant for understanding the hydrocarbon generation mechanisms,organic-inorganic interactions,and carbon cycle.  相似文献