Hydrocarbon Generation and Expulsion of the Upper Triassic T3x5Source Rocks in the Western Sichuan Depression: Assessment for Unconventional Natural Gas

Tight-sand gas in the Jurassic and shale gas within the fifth member of Xujiahe Formation （T3xs） in the Western Sichuan Basin （WSD） are currently regarded as the most prolific emerging unconventional gas plays in China. This study conducted a conventional evaluation of T3x5 source rocks in the WSD, and investigated their hydrocarbon generation and expulsion characteristics, including intensity, efficiency and amount. The results show that, the T3x5 source rocks are thick （generally 〉200 m）, and have a high total organic content （TOC）, ranging from 2.5 to 4.5 wt%. It is thus indivative of a great hydrocarbon generation potential when they underwent high thermal evolution （Ro〉1.2%） in the area. In addition, an improved method of hydrocarbon generation potential is applied, indicating that the source rocks reached a hydrocarbon expulsion threshold with vitrinite reflectance （Ro） reaching 1.06%. and that the comprehensive hydrocarbon expulsion efficiency is about 60%. The amount of hydrocarbon generation and expulsion from Tax5 source rocks is 3.14x10^10 t and 1.86x10^10 t, respectively, with a residual amount of 1.28x10^10t within them. Continuous-type tight-sand gas is predicted to have developed in the Jurassic in the Chengdu Sag of the WSD because of the good source-reservoir configuration; the Jurassic sandstone reservoirs are tight, and the gas expelled from the T3xs source rocks migrates for very short distances vertically and horizontally. The amount of gas accumulation in the Jurassic reservoirs derived from T3x5 source rocks is up to 9.3x10s t. Geological resources of shale gas are up to 1.05x10TM t. Small differences between the amounts calculated by the volumetric method and those obtained by hydrocarbon generation potential method may be due to other gas accumulations present within interbedded sands associated with gas shales.

Three-Dimensional Structural Modelling and Source Rock Evaluation of the Quseir Formation in the Komombo Basin,Egypt

The Quseir Formation consists mainly of dark gray mudstones with a high organic matter content and excellent hydrocarbon-generating potential.The main objectives of this study are to highlight the dominant structural elements in the Komombo Basin,Egypt,and evaluate the geochemical characteristics of the Quseir Formation.Depth maps and a 3 D structural model indicate two normal fault trends NW–SE and ENE–WSW.The NW–SE trend is the dominant one that created the primary half-graben system.The depth to the top of the Quseir Formation gradually decreases from the eastern and central parts towards the corners of the basin.The thickness of the Quseir Formation ranges from about 300 to 1000 ft.The 3 D facies model shows that the shale has a large probability distribution in the study area,compared with the sandstone and siltstone.The source rock potential varies between good in the western part to very good in the eastern part of the basin.The organic-rich interval is dominated by gas-prone kerogen type III based on TOC and Rock-Eval.The pyrolysis data vitrinite reflectance(%Ro)(0.5–0.74%)and Tmax values(406–454 C°)suggest a maturity level that ranges from immature to early maturity stage for hydrocarbon generation.

Evaluation of source rocks and prediction of oil and gas resources distribution in Baiyun Sag,Pearl River Mouth Basin,China

By conducting organic geochemical analysis of the samples taken from the drilled wells in Baiyun Sag of Pearl River Mouth Basin,China,the development characteristics of hydrocarbon source rocks in the sag are clarified.Reconstruct the current geothermal field of the sag and restore the tectonic-thermal evolution process to predict the type,scale,and distribution of resources in Baiyun Sag through thermal pressure simulation experiments and numerical simulation.The Baiyun Sag is characterized by the development of Paleogene shallow lacustrine source rocks,which are deposited in a slightly oxidizing environment.The source rocks are mainly composed of terrestrial higher plants,with algae making a certain contribution,and are oil and gas source rocks.Current geothermal field of the sag was reconstructed,in which the range of geothermal gradients is(3.5–5.2)℃/100 m,showing an overall increasing trend from northwest to southeast,with significant differences in geothermal gradients across different sub-sags.Baiyun Sag has undergone two distinct periods of extensional process,the Eocene and Miocene,since the Cenozoic era.These two periods of heating and warming events have been identified,accelerating the maturation and evolution of source rocks.The main body of ancient basal heat flow value reached its highest at 13.82 Ma.The basin modelling results show that the maturity of source rocks is significantly higher in Baiyun main sub-sag than that in other sub-sags.The Eocene Wenchang Formation is currently in the stage of high maturity to over maturity,while the Eocene Enping Formation has reached the stage of maturity to high maturity.The rock thermal simulation experiment shows that the shallow lacustrine mudstone of the Wenchang Formation has a good potential of generating gas from kerogen cracking with high gas yield and long period of gas window.Shallow lacustrine mudstone of the Enping Formation has a good ability to generate light oil,and has ability to generate kerogen cracking gas in the late stage.The gas yield of shallow lacustrine mudstone of the Enping Formation is less than that of shallow lacustrine mudstone of the Wenchang Formation and the delta coal-bearing mudstone of the Enping Formation.The numerical simulation results indicate that the source rocks of Baiyun main sub-sag generate hydrocarbons earlier and have significantly higher hydrocarbon generation intensity than other sub-sags,with an average of about 1200×10^(4)t/km^(2).Oil and gas resources were mainly distributed in Baiyun main sub-sag and the main source rocks are distributed in the 3^(rd)and 4~(th)members of Wenchang Formation.Four favorable zones are selected for the division and evaluation of migration and aggregation units:No.(1)Panyu 30 nose-shaped structural belt,No.(3)Liuhua 29 nose-shaped uplift belt and Liwan 3 nose-shaped uplift belt,No.(2)gentle slope belt of Baiyun east sag,and No.(8)Baiyun 1 low-uplift.

Evaluation of abundant hydrocarbon-generation depressions in the deepwater area of Qiongdongnan Basin,South China Sea

It has been confirmed that the key source rocks of Qiongdongnan Basin are associated with the Yacheng Formation, which was deposited in a transitional marine-continental environment. Because the distribution and evolution patterns of the source rocks in the major depressions are different, it is important to determine the most abundant hydrocarbon-generation depressions in terms of exploration effectiveness. Based on an analysis of organic matter characteristics of the source rocks, in combination with drilling data and seismic data, this paper establishes a model to evaluate the hydrocarbon-generation depressions in the deepwater area of Qiongdongnan Basin. First of all, by using the method of seismic-facies model analysis, the distribution of sedimentary facies was determined. Then, the sedimentary facies were correlated with the organic facies, and the distribution of organic facies was predicted. Meanwhile, the thickness of source rocks for all the depressions was calculated on the basis of a quantitative analysis of seismic velocity and lithology. The relationship between mudstone porosity and vitrinite reflectance（Ro） was used to predict the maturity of source rocks. Second, using the parameters such as thickness and maturity of source rocks, the quantity and intensity of gas generation for Yacheng and Lingshui Formations were calculated. Finally, in combination with the identified hydrocarbon resources, the quantity and intensity of gas generation were used as a guide to establish an evaluation standard for hydrocarbon-generation depressions, which was optimized for the main depressions in the Central Depression Belt. It is proposed that Lingshui, Ledong, Baodao and Changchang Depressions are the most abundant hydrocarbon depressions, whilst Songnan and Beijiao Depressions are rich hydrocarbon depressions. Such an evaluation procedure is beneficial to the next stage of exploration in the deep-water area of Qiongdongnan Basin.

Hydrocarbon generating-potential and maturity-related changes of the Khatatba Formation, Western Desert, Egypt

The petroliferous province of the Western Desert comprises several sedimentary basins with different hydrocarbon potentiality and production capability.The middle Jurassic Khatatba Formation was proved a potential source rock in some basins and active/effective in others.The current study aims to give a comprehensive assessment and evaluation of the potential organic-rich intervals of the Khatatba Formation across JG and JD fields,northeast Abu Gharadig Basin(NEAG).The hydrocarbon generating capability and sourcing of the Khatatba Formation studied through organic geochemistry calibrated with well logging.However,the efficiency of some widely used plots of geochemistry is re-evaluated according to their accuracy and consistency.Forty cuttings,thirteen cores and two oil samples obtained from three wells(JG-2,JG-3 and JD-4)were evaluated.The samples revealed total organic carbon(TOC)values ranging from 1 to 9 wt%,exhibiting a good-excellent potential source rock.A single sample in the JD-4 well attained a TOC value of 21.3 wt%with a generating potential(represented by S2 parameter)exceeding 146 mgHc/g rock required a special evaluation.Most of the samples(mainly in the JD-4 well)attained a sufficient level of thermal maturity for hydrocarbon generation with a Tmax up to 449
C.The vitrinite reflectance(%Ro)values(a common maturity-related indicator)acquired from the JD-4 well ranging between 0.76%and 0.92%.These values are tediously increasing with depth indicating a uniform geothermal regime.The Khatatba organofacies,with wide variety of kerogen types(I,II,II-S and II/III),contain marine organic matter with a slight terrigenous input,exhibiting anoxic-suboxic environmental conditions.Oil-source correlations define the organic-rich intervals responsible for charging the accumulated hydrocarbon in the NEAG concession.