Source Rock Prediction Research Articles

Geochemical characteristics and classification of Oligocene source rocks with different facies in Bozhong Sag, Bohai Bay Basin, East China

There have been many studies conducted on the Eocene source rocks (Shahejie Formation Mbrs 1 and 3) (E2s1 and E2s3) of the Bozhong Sag, Bohai Bay Basin in East China. However, Oligocene source rocks (Dongying Formation Mbrs 2 and 3) (E3d2 and E3d3) have also made significant contributions to petroleum accumulations in this region. Their organic matter (OM) enrichment mechanisms, environmental and ecological variations, and laterally variable facies remain subjects of debate, particularly in the lower Dongying Formation Mbrs 2 (E3d2L). Thus, we investigated the geochemical properties, depositional environments, and OM origins of E3d2L and E3d3 source rocks from seven prospecting wells in southwestern Bozhong Sag. Our findings indicate that E3d2L source rocks are of poor-to-medium quality, whereas E3d3 source rocks are classified as good-to-excellent quality. Notable differences in the geochemical characteristics between E3d2L and E3d3 source rocks were observed. Hierarchical cluster analysis identified five genetic organic facies. The E3d2L source rocks comprises facies D2-Ⅰ, D2-Ⅱ, D2-Ⅲ, and D2–D3, whereas E3d3 contains facies D3 and D2–D3, with D2–D3 being common to both source rocks. Additionally, an integrated OM enrichment model was established to evaluate Oligocene source rocks. The five genetic organic facies exhibit distinctive differences and some similarities regarding redox conditions, water salinity, and OM origins. Their geochemical characteristics within the same intervals display pronounced lateral heterogeneity from deep source rocks deposits to more marginal water depths. The established model provides guidance for the prediction and exploration of effective Oligocene source rocks in the Bohai Sea and research on the Paleogene and Neogene petroleum systems. Moreover, the integration of biomarkers and hierarchical cluster analysis methods for organic facies analysis has significant implications for predicting of source-rock heterogeneity in other lacustrine rift basins.

Source Rock Prediction Using Well Log and Seismic Data: A Study of the Albian Stage in the Côte d’Ivoire Basin

The Côte d’Ivoire Basin is one of the most important oil production areas in Africa; and it is also the focus of global oil and gas exploration, but the degree of oil exploration and development in this basin are still in the early stages. Based on a comprehensive analysis of drilling, logging, and geochemical data in the Côte d’Ivoire Basin, this study comprehensively evaluates the Cretaceous lacustrine source rocks in the study area, establishes a total organic carbon (TOC) quantitative prediction model by using the total organic carbon method, determines the relationship between seismic reflections and the geochemical characteristics of the source rocks, and tracks the main source rocks horizontally. The results show that the TOC of the Lower Cretaceous Albian stage source rocks is 2.63 wt.%, the kerogen type II is dominant, and the vitrinite reflectance (RO) ranges from 0.3% to 0.9%. The source rocks are mainly in the low-mature to mature stage, and they are generally of good and premium quality. The distribution range of high-quality source rocks with TOC values of 4.00~5.00% is predicted using the total organic carbon method, and useing the seismic method, we determine that high-quality source rocks with larger thickness values and better continuity are mainly developed in the eastern depression center of the basin.

Chemical Characteristics and Distribution Prediction of Hydrocarbon Source Rocks in the Continental Lacustrine Basin of the Chang 7 Member in the Heshui Area of the Ordos Basin, China

The Heshui area within the Ordos Basin holds significant strategic importance for the extraction and development of tight oil resources in the Changqing Oilfield. This study extensively explored the geochemical features and distribution tendencies of source rocks in the Chang 7 member, utilizing core samples and logging data for a comprehensive analysis. A more advanced model was utilized to predict the dispersion of Total Organic Carbon (TOC) in the Chang 7 member source rock. The properties and hydrocarbon generation potential of source rocks were thoroughly assessed through a comprehensive analysis that involved evaluating their total organic carbon content, pyrolysis parameters, and reflectance (Ro) values. The research concluded that the source rocks boast substantial organic matter, predominantly categorized as type II-I organic material. The thermal maturation levels span from low maturity to maturity, signifying significant potential for oil generation. Generally, the source rock quality falls within the range of good to excellent. Sedimentary patterns notably influence the distribution of hydrocarbon-source rocks. The northeastern sector of the study area is situated in an area characterized by deep to semi-deep lake sedimentation, making it the primary location for the presence of Chang 7 member hydrocarbon source rocks. With a thickness ranging from 40 to 70 m, this zone becomes a pivotal focus for the potential exploration of tight oil resources in the future. The results of this study offer crucial insights for understanding the geochemical characteristics of hydrocarbon source rocks, evaluating their potential for hydrocarbon generation, and forecasting favorable zones for oil and gas exploration in similar regions.

Prediction and quantification of effective gas source rocks in a lacustrine basin: Western Depression in the Liaohe Subbasin, China

Due to limited data on the geochemical properties of natural gas, estimations are needed for the effective gas source rock in evaluating gas potential. However, the pronounced heterogeneity of mudstones in lacustrine successions complicates the prediction of the presence and geochemical characteristics of gas source rocks. In this paper, the Liaohe Subbasin of Northeast China is used as an example to construct a practical methodology for locating effective gas source rocks in typical lacustrine basins. Three types of gas source rocks, microbial, oil-type, and coal-type, were distinguished according to the different genetic types of their natural gas. A practical three-dimensional geological model was developed, refined, and applied to determine the spatial distribution of the mudstones in the Western Depression of the Liaohe Subbasin and to describe the geochemical characteristics (the abundance, type, and maturation levels of the organic matter). Application of the model in the subbasin indicates that the sedimentary facies have led to heterogeneity in the mudstones, particularly with respect to organic matter types. The effective gas source rock model constructed for the Western Depression shows that the upper sequence (SQ2) of the Fourth member (Mbr 4) of the Eocene Shahejie Formation (Fm) and the lower and middle sequences (SQ3 and SQ4) of the Third member (Mbr 3) form the principal gas-generating interval. The total volume of effective gas source rocks is estimated to be 586 km3. The effective microbial, oil-type, and coal-type gas source rocks are primarily found in the shallow western slope, the central sags, and the eastern slope of the Western Depression, respectively. This study provides a practical approach for more accurately identifying the occurrence and geochemical characteristics of effective natural gas source rocks, enabling a precise quantitative estimation of natural gas reserves.

Application of Iterative Virtual Events Internal Multiple Suppression Technique: A Case of Southwest Depression Area of Tarim, China

The seismic records in the Cambrian southwest depression of the Tarim Basin exhibit discrepancies when compared to the actual geological setting, which is caused by the presence of multiples. Despite the application of the Radon transform, multiple interferences persist beneath the Cambrian salt in the pre-stack data, with significant variations in energy and frequency across the horizontal direction. In addition, other multiple suppression methods are also difficult to handle this problem. To address this issue, we have developed an iterative virtual event internal multiple suppression method for post-stack data. This novel algorithm extends the traditional virtual event internal multiple suppression approach, eliminating the need for data regularization and avoiding the problem of the traditional virtual events method requiring sequential extraction of primaries from relevant layers, which greatly improves computational efficiency and simplifies the implementation steps of the traditional method. Numerical experiments demonstrate the efficacy of our method in suppressing internal multiples in both synthetic and field data while preserving primary signals. When applied to real seismic data profiles, the iterative method yields structural characteristics that align more closely with sedimentary laws and reduces disparities in energy and frequency of multiples along the horizontal axis. Consequently, our method provides a robust foundation for subsequent hydrocarbon source rock prediction.

Geochemical Characteristics and Development Model of the Coal-Measure Source Rock in the Kuqa Depression of Tarim Basin

The development model of the coal-measure source rock may be different from that of the lacustrine source rock. The depositional environment of the coal-measure source rock is dominated by weak oxidation and weak reduction, and the majority of the organic material originates from terrestrial higher plants. Taking the Jurassic coal-measure source rock in the Kuqa Depression as the research object, the geochemical characteristics of the source rock are comprehensively analyzed, the primary controlling elements of source rock development are made clear, and the development model of the coal-measure source rock is established. This study contributes to the field of source rock prediction and oil and gas exploration. The lithology of the coal-measure source rock in the Kuqa Depression is mainly mudstone, carbonaceous mudstone, and coal, which are medium- to good-quality source rocks, and the organic matter type is mainly II2 and III. Terrestrial organic matter is a key factor in controlling the formation of coal-measure source rocks, and the sedimentation rate also has a certain influence. The redox degree of the depositional environment, water salinity, and clay mineral content has little influence on the development of coal-measure source rocks. By integrating the main control factors, the development model of the coal-measure source rock is established. It is considered that the development model and distribution characteristics of the coal-measure source rock are different from the traditional understanding of lacustrine source rocks, and it is pointed out that the coal-measure source rock in the gentle slope zone is more developed than the sag area.

Seismic response analysis and distribution prediction of source rocks in a survey of the South China Sea

Identification and prediction of high-quality source rocks is the key to obtaining new resources in the exploration area of Cenozoic basins in offshore China. We research the seismic response and distribution of hydrocarbon source rocks using seismic data, well curves, lithologic interpretation, and geochemical analysis. The target is the source rock development zone of the W Formation in a survey of the South China Sea. The results show that the seismic response of thick layer source rocks differ from surrounding rocks in the seismic profile (strong reflections with opposite polarity at the top and bottom and messy or chaotic reflections inside). Seismic reflections of interlayer source rocks have the characteristics of low frequency and continuous strong amplitude. The dominant frequency and maximum amplitude decrease as the number of mudstone layers increases. Through seismic petrophysical analysis, we have obtained three sensitive parameters of source rock in this survey: clay content, P-wave impedance, and elastic impedance. Different classification methods can realize the classification and prediction of hydrocarbon source rocks, among which the Kernel Fisher discriminant analysis method is the best. The prediction results are consistent with the geological background, geochemical information, and well curves.

Recognition and Prediction of Source Rocks of the Madingo Formation in the Lower Congo Basin

Recognition and Prediction of Source Rocks of the Madingo Formation in the Lower Congo Basin

Depositional environment and hydrocarbon potential of Early Permian coals deposit in the Huanghua Depression, Bohai Bay Basin

The Carboniferous-Permian was an important period for the formation of coal mines and coaly source rocks across the world. Controlled by the paleoclimate, Cathaysia flora, and transitional sedimentary environment of the delta, the Early Permian Shanxi Formation in the Huanghua Depression formed several layers of coal and coaly source rocks that can be explored in the whole depression. However, the development regularity and distribution prediction of high-quality coaly source rocks are still not well understood. The coaly source rocks of the Shanxi Formation in the Huanghua Depression were taken as the research object. With the determination and analysis of organic carbon content, rock pyrolysis, and vitrinite reflectance, we found that the organic matter abundance (i.e., TOC which changed from 20.3 % to 80.0 %), hydrocarbon generation potential (i.e., S1 + S2 which varied from 7.82 mg/g to 208.81 mg/g), and kerogen types (mainly type II2) of the coal were better than carbonaceous mudstone and coaly shale. Maceral component identification indicated that coal and carbonaceous mudstone had more liptinite (i.e. cutinite and sporinite)and hydrogen-rich vitrinite, while coaly shale was mainly composed of hydrogen-poor vitrinite and a small amount of liptinite. The analysis of the ratios of major and trace elements, normal alkanes, and isoparaffin suggested that the paleo-water salinity of coal and carbonaceous mudstone deposition was more than that of part coaly shale. Revealed by the weak reduction of their depositional environment, the development of high-quality coal and carbonaceous mudstone was mostly controlled by the input of oil- and gas-prone organic matter. The formation of high-quality coaly shale was chiefly dominated by a strong reduction environment with an insignificant amount of organic matter input. The formation model of high-quality coaly source rocks was established. This model can be used to predict the distribution of coal mines and coaly source rocks in the Huanghua Depression and Bohai Bay Basin.

POTENTIAL SOURCE ROCKS EVALUATION FOR THE PRE-SALT COMPLEX OF THE EASTERN EDGE OF PRECASPIAN BASIN

Through basin analysis, the major tectonic stages and paleogeographic conditions of the formation of potential oil and gas source rocks of the subsalt complex of the eastern side zone of the Precaspian basin are considered. Prediction and localization of potential source rocks is critical for the Precaspian petroleum system understanding, both during petroleum play assessment at the prospecting and exploration stages. The generation and emigration potential of the oil and gas basin is determined not only by the concentration of the initial organic matter in the rock, but also by the type of kerogen. Based on Rock-Eval studies and comparative analysis with published biomarker data, the generation potential, genetic type and thermal maturity are analyzed depending on the age and structural relatedness of potential source rocks. A high generation potential has been established for the Lower Permian deposits, the occurrence of multiple generation foci controlled by the type and concentration of organic matter is predicted, which led to the formation of specific reservoirs of the "akzharite" type. The generation potential of the Visean-Bashkirian deposits is poor to average, catagenetic unconformities have been established within KT-II, KT-I, which indicates erosions, the total organic carbon (TOC) is 0.1-4%, the hydrogen index increases with depth, for samples enriched with TOC and with a content of S2 > 1, type II kerogen has been established, which it is an indicator of reducing marine environment. 2D basin modeling was performed in order to reconstruct the thermal evolution of potential source rocks and their thermal maturity and transformation ratio were modelled to determine the regional characteristics of hydrocarbon generation and migration. It is assumed that the formation and distribution area of the primary source rocks is associated with reducing conditions of the deep-sea shelf and continental slope and intensive subsidence in the Late Devonian-Lower Permian times. Conducting a comprehensive analysis of paleogeographic and paleotectonic conditions for the formation of potential source rocks is of key importance in the seismic interpretation and reconstruction of thermal history. 2D basin modeling was performed in order to reconstruct the thermal history of potential oil-producing strata and the degree of catagenetic maturity and the kerogen maturity index were estimated to determine the regional characteristics of hydrocarbon generation and migration.

Nonlinear seismic inversion by physics-informed Caianiello convolutional neural networks for overpressure prediction of source rocks in the offshore Xihu depression, East China

Pressure prediction has long been one of subject of research focuses in petroleum geology and exploration, but is traditionally limited to moderately overpressured formations due to disequilibrium compaction based on the empirical velocity-pressure model. Overpressures in the Xihu depression are caused by fluid expansion due to the generation of natural gas in source rocks. The resulting abnormally pressured gas reservoirs manifest as a high-pressure structure with the thick mud-coated thin sand (MCS) that remains largely unaddressed in prediction. Such gas-producing overpressures make traditional prediction methods unapplicable because of the significant influence of high gas contents on seismic velocities. We employ a frequency-dependent quality factor Q–pressure petrophysical model because of the sensitivity of acoustic attenuation to overpressures. However, acoustic attenuations from rock physics and sonic logging present an uncertain dependence on pore pressures. This implies that overpressure prediction is a typical physical system that is characterized by both deterministic mechanism and statistical behavior, which resorts to physics-informed deep learning methods. We take the Q–pressure petrophysical model as the activation function of Caianiello convolutional neurons with an attempt to combine deterministic and statistical mechanisms for overpressure prediction. Such convolutional neurons render strong feature extraction and powerful learning ability and are used to construct physics-informed Caianiello convolutional neural networks (CCNNs) for overpressure prediction in the Xihu depression. The comprehensive CCNNs-based seismic inversion scheme for overpressures consists of reservoir petrophysical modeling, deep learning for neural wavelets, well-seismic correlation analysis, deconvolution-based inversion for an initial pressure model, and input-signal reconstruction to improve the initial pressure model. With drill stem tests (DSTs), well logs, and 3D seismic data, we conduct the overpressure prediction associated with cross validation in the Xihu depression, which demonstrates the applicability of the physics-informed CCNNs inversion scheme. Predicting reliability away from the training wells usually depends on the geological complexity of areas under study. Nevertheless, the information representation in the trained CCNNs can be improved gradually by feeding new well data during the development of an oil field.

Prediction of major source rocks distribution in the transition from depressed to rifted basin using seismic and geological data: The Guyang to Linhe Formations in the Linhe Depression, Hetao Basin, China

Source rock prediction in the Linhe Depression is exceptionally difficult owing to inadequate data, while the process by which depressed-rifted conversion influences source rock distribution remains unclear. Thus, this study aimed to predict source rock distribution and demonstrate its influencing factors. Based on outcrop, geochemical, well log, and seismic information, a seismic methodology involving the prediction of organic facies distribution using seismic facies analysis and mudstone thickness via a seismic velocity-lithology model was applied to predict source rocks. Our study showed the suitability of this method for early exploration in basins with inadequate data. The correlation coefficient between the predicted and borehole values of mudstone was 0.94, and the relative error was <14.6%. The optimal source rocks in the second member of the Guyang Formation were encountered in new wells JHZK9, LHC1, and JH14 and accurately predicted, thereby validating our methodology. Furthermore, optimal source rocks transitioned from broad to limited distributions, moved closer to the boundary fault, and transferred from gentle slopes to deep sags during the depression to rift period. This transition dominated the distribution of source rocks. The basin type restricted the location of source rocks, and the transfer of lacustrine centers played a leading role in the distribution and differential superimposition of source rocks. Additionally, differential compression influenced source rock thickness in the second member of the Guyang Formation, while segmented variations in the boundary fault style and activity rate influenced the thickness in the second member of the Linhe Formation.

Basin-filling processes and hydrocarbon source rock prediction of low-exploration degree areas in rift lacustrine basins: a case from the Wenchang Formation in low-exploration degree areas, northern Zhu I Depression, Pearl River Mouth Basin, E China

Hydrocarbon source rocks, as a main geologic factor of petroliferous systems in a sedimentary basin, play a key role in the accumulation of oil and gas and the formation of hydrocarbon accumulations. This study, which focuses on difficulties in prediction of hydrocarbon source rocks in basins or sags with low exploration degree and insufficient hydrocarbon source rock indicators, taking the Wenchang Formation of northern Zhu I Depression, Pearl River Mouth Basin as an example, proposed a hypothesis of “finding lakes and hydrocarbon source rocks”. Detailed steps include, first, determination of the lacustrine basin boundary according to analysis of seismic foreset facies, determination of the depositional area based on the compilation of strata residual thickness maps, determination of the lacustrine basin shape according to deciphering slope break belt system, determination of the fluctuation of paleo-water depth according to biogeochemical indicators of mature exploration areas, determination of the lacustrine basin scale based on analyses of tectonics intensity and accommodation space, which prove the existence of the lacustrine basin and identify the range of semi deep-deep lake; second, further analyses of tectonopalaeogeomorphology, paleo-provenance, palaeoclimate and paleo-water depth to reconstruct the geologic background of the original basin and semi-deep-deep lacustrine facies, to determine the distribution of semi-deep/deep lacustrine sediments in combination with studies of logging facies, core facies, seismic facies and sedimentary facies, and to rank the sags’ potential of developing hydrocarbon source rocks from controlling factors of source-to-sink system development; third, on the basis of regional sedimentary facies analysis, through identification and assessment of seismic facies types of semi-deep/deep lacustrine basins in mature areas, establishing “hydrocarbon source rock facies” in mature areas to instruct the identification and depicting of hydrocarbon source rocks in semi-deep/deep lacustrine basins with low exploration degree; fourth, through systematical summary of hydrocarbon-rich geological factors and lower limit index of hydrocarbon formation of the sags already revealed by drilling wells (e.g., sag area, tectonic subsidence amount, accommodation space, provenance characteristic, mudstone thickness, water body environment, sedimentary facies types of hydrocarbon source rocks), in correlation with corresponding indexes of sags with low exploration degree, then the evaluation and sorting of high-quality source rocks in areas with sparsely distributed or no drilling wells can be conducted with multi-factors and multiple dimensions. It is concluded that LF22 sag, HZ10 sag and HZ8 sag are II-order hydrocarbon rich sags; whereas HZS, HZ11 and HZ24 are the III-order hydrocarbon-generating sags.

Total organic carbon content prediction of source rocks with conventional well log data based on regression committee machine

Total organic carbon content prediction of source rocks with conventional well log data based on regression committee machine

Formation and evolution of coal– and oil–bearing source rocks in the Lower Cretaceous Shahai Formation in the Fuxin Basin (NE China): Evidence from organic and inorganic geochemical analyses

Two source rocks were deposited in the Lower Cretaceous Shahai Formation (K1sh) in the Fuxin Basin (NE China): the third Member (K1sh3) coal–bearing and the fourth Member (K1sh4) oil–bearing source rock. However, the differences between the two Fuxin Basin source rocks remain poorly constrained. This study systematically reveals the formation and evolution of these source rocks through sedimentological and geochemical analyses. During the K1sh3 deposition, the intermittently warm–humid climate promoted organic matter (OM) input from terrestrial plants. Meanwhile, the restricted swamp with suboxic water conditions enhanced OM preservation and reduced OM dilution. Thus, warm–humid climate, suboxic water conditions of swamp controlled the formation of excellent coal–bearing source rock with highest total organic carbon (TOC) content (avg. 28.68 wt%) and Type III kerogen (perhydrous). The post–mature maturity (avg. 484 °C Tmax) indicates that the K1sh3 coal–bearing source rocks have reached the wet to dry gas generation stage.During the K1sh4 deposition, rapid basin subsidence and a humid–prone climate resulted in lake expansion, enhancing the dysoxic bottom water conditions. Moreover, the rapid basin subsidence triggered frequent gravity flows. The turbidity flows delivered terrestrial OM fragments and nutrients, promoting the lacustrine productivity and producing OM dominated by aquatic organisms with some terrestrial plants. However, hyperconcentrated density flows disturbed the dysoxic bottom water conditions and strongly diluted the OM. Hence, the humid–prone climate, dysoxic bottom water conditions and gravity flows have controlled the formation of the K1sh4 oil–bearing source rock with high TOC contents (avg. 2.73 wt%). The oil–bearing source rocks show good hydrocarbon potential (avg. 6.17 mg HC/g rock S2) and Type II to III kerogen (perhydrous). The mature oil–bearing source rocks (avg. 443 °C Tmax) in the lower K1sh4 were at the oil generation peak and may be the chief source rock in the Fuxin Basin. During the Early Cretaceous, similar rift basins were developed in Northeast China, so this study provides a typical sample for source rock prediction in other adjoining rift basins.

Characteristics and controlling factors of lacustrine source rocks in the Lower Cretaceous, Suhongtu depression, Yin-E basin, Northern China

Lacustrine source rocks are widely distributed in the Mesozoic rift basins of northern China. Two lacustrine rift sub-depressions in the Suhongtu depression, Yin-E Basin, have been subjected to a comprehensive analysis of their source rock potential to further reveal the controlling factors and enrichment mechanisms by constructing models for lacustrine source rocks in different tectonic settings. The Hari sag in the Suhongtu depression has significantly greater sedimentary cover and better hydrocarbon generation conditions when compared to the Babei sag by comprehensive analyses of total organic carbon (TOC), chloroform bitumen “A”, Rock-Eval pyrolysis and δ13CPDB. The results show that source rock deposition was affected by organic productivity, organic matter preservation and sedimentation rates. The TOC and δ13CPDB values indicate that there was higher productivity in the lakes of the Hari sag, and productivity reached a maximum during the deposition of the Yingen Formation. The total reduced sulphur (TRS), Pr/Ph, and gammacerane index values indicate that a relative reducing environment was present in the Hari sag. During deposition of the Bayingebi Formation in the Hari sag, the water was suboxic-anoxic, gradually turning anoxic and finally formed a strongly reducing, high-salinity, stratified water environment during deposition of the Yingen Formation. The Babei sag was suboxic-oxidizing throughout the deposition of the Lower Cretaceous lacustrine mudstones. With more active boundary faults and higher sedimentation rates, the terrigenous organic matter inputs to the Hari sub-depression were higher than those in the Babei sub-depression. These observations permitted the development of a model for the formation mechanism for the effective lacustrine source rocks in the Cretaceous fault basin of the Suhongtu depression. In the Hari sag, during source rock deposition of the K1b and K1s formations, intense and more active faults resulted in high terrigenous organic matter being carried into the lake. However, rapid sedimentation rates caused organic matter dispersed. During source rock deposition of the K1y Formation, the sag entered a transition stage from synrift to post-rift with an intermediate sedimentation rate. More organic matter was continuously transported into the basin with high salinity and a strongly reducing sedimentary environment, which caused enrichment of organic matter. In the Babei sag, due to small-scale rifting structures and shallow water conditions, a relatively low influx of terrigenous organic matter and suboxic to oxidizing conditions were developed. This study have important implications for source rock prediction in other lacustrine rift basins.

Fine evaluation and favorable area prediction of deep source rocks in northern Songliao Basin

Focusing on Xujiaweizi fault depression, the geological conditions and geochemical characteristics of deep natural gas formation in the north of Songliao basin are evaluated, the natural gas resources are estimated, and the favorable areas are optimized. Shahezi Formation shale is a set of coal bearing sediments with high organic matter abundance (TOC is 1%～12%), high over maturity (Ro is 1%～4%) and shore shallow lake facies, which are mainly distributed in Xujiaweizi fault depression, Gulong-Lindian fault depression and Yingshan fault depression. The thickness, TOC, Ro and hydrocarbon generation of four thirdorder sequences with different lithology (mudstone and coal) are carefully evaluated for the Shahezi Formation shale in the deep layer of Songbei. The comprehensive evaluation shows that the mudstone thickness of Es4 member in Anda and Xuzhong areas of Xujiaweizi fault depression is large (150 ~ 525m), TOC is high (1% ~ 4%), thermal evolution degree is high (Ro is 1.2% ~ 3.4%), and gas generation intensity is high (20 ~ 815) × 108m3 / t), moderate buried depth (3000~4500m) and overlapping area of 756km2. It is a favorable exploration area for natural gas and shale gas in Daqing Oilfield.

Organic matter accumulation in the Upper Cretaceous Qingshankou and Nenjiang Formations, Songliao Basin (NE China): Implications from high-resolution geochemical analysis

Abstract The Songliao Basin is well-known as one of most prolific petroleum basins in China. Information regarding Upper Cretaceous organic matter (OM) accumulation within black shales of the Qingshankou and Nenjiang Formations (Fm) can be obtained by geochemical analyses. Two oil shale successions at the bottom of the Qingshankou Fm first member (K2qn1) and Nenjiang Fm second member (K2n2) are investigated in high resolution to reveal the factors that govern OM accumulation. Within the two target profiles, combined petrological and geochemical results indicate that OM accumulation can be divided into two phases: (i) a lower phase characterized by high primary productivity, enhanced input of terrigenous OM and anaerobic conditions of OM deposition (TOC maximum 18.25 wt%) and (ii) an upper phase of lower primary productivity and anoxic to dysoxic conditions in bottom water (TOC maximum 9.45 wt%). Alternations of warmer and wetter climatic conditions provided the nutrients, and fluctuations in lake level are suggested to be responsible for differences in redox conditions and bioproductivity between the two phases. Marine ingressions enhanced OM preservation by promoting bottom water salinity (e.g., anaerobic conditions with brackish-saline water within K2qn1 lower phase). The identification of different OM accumulation mechanisms by high-resolution geochemical analyses are expected to improve the prediction of high quality source rocks within uniform depositional environments.

Geophysical Prediction Technology Based on Organic Carbon Content in Source Rocks of the Huizhou Sag, the South China Sea

Abstract Due to the high exploration cost, limited number of wells for source rocks drilling and scarce test samples for the Total Organic Carbon Content (TOC) in the Huizhou sag, the TOC prediction of source rocks in this area and the assessment of resource potentials of the basin are faced with great challenges. In the study of TOC prediction, predecessors usually adopted the logging assessment method, since the data is only confined to a “point” and the regional prediction of the source bed in the seismic profile largely depends on the recognition of seismic facies, making it difficult to quantify TOC. In this study, we combined source rock geological characteristics, logging and seismic response and built the mathematical relation between quasi TOC curve and seismic data based on the TOC logging date of a single well and its internal seismic attribute. The result suggested that it was not purely a linear relationship that was adhered to by predecessors, but was shown as a complicated non-linear relationship. Therefore, the neural network algorithm and SVMs were introduced to obtain the optimum relationship between the quasi TOC curve and the seismic attribute. Then the goal of TOC prediction can be realized with the method of seismic inversion.

Biogeochemistry of intertidal microbial mats from Qatar: New insights from organic matter characterisation

Understanding early organic matter (OM) alteration and preservation in marine carbonate-evaporite systems could improve understanding of carbon cycling and hydrocarbon source rock prediction in such environments. It is possible that organic-rich microbial mats are important contributors to preserved hydrocarbons and, to explore this, we examined changes in lipid composition in such a mat from a mesohaline intertidal lagoon, eastern Qatar. The mat reaches>5cm thickness over a carbonate mud substrate, rich in seagrass, gastropods and other small bioclasts. Clear lamination, with distinct downward colour changes from green to pink to brown, reflects different microbial mat communities. The layers contain spheroids of probable dolomite, the precipitation of which was plausibly bacterially-mediated. Lipids [n-alkanes, fatty acids (FAs), hopanoids, isoprenoid hydrocarbons, dialkyl glycerol diethers (DAGEs), and isoprenoid (0–4) and branched (Ia–IIIa) GDGTs] reflected the diverse mat-building phototrophic, heterotrophic and chemoorganotrophic microorganisms, as well as some likely allochthonous material (i.e. steroids, n-alkanols, high molecular weight n-alkanes). The lipids clearly documented the change in microbial community, with phytene(s) being the predominant hydrocarbon in the phototrophic surface layer. O2 and pH dropped significantly 0.2cm below the mat surface, coincident with the predominance of Deltaproteobacteria and increased concentrations of archaeal and bacterial glycerol dialkyl glycerol tetraether lipids and C15/C16 and C16/C17 dialkyl glycerol ether lipids in the deeper layers. Archaeol, likely of methanogen origin, was most abundant in the deepest layer. Allochthonous inputs occurred throughout the mat, including abundant steroids, especially dinosterol and dinostanol, possibly related to periodic algal (dinoflagellate) blooms in the Arabian Gulf. Both n-alkanes and n-alkanols appeared to be derived from seagrass. OM content decreased in the deepest mat; this suggests an overall low preservation potential of OM in intertidal mesohaline-hypersaline mats of the Arabian Gulf, which in turn suggests that these are not the major source of hydrocarbons in microbially-dominated carbonate-evaporite systems.