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In vivo levels of reactive oxygen species (ROS) and reactive nitrogen species (RNS) are critical to many physiological and pathological processes. Because of the distinct differences in their biological generation and effects, simultaneously visualizing both of them could help deepen our insights into the mechanistic details of these processes. However, real-time and deep-tissue imaging and differentiation of ROS- and RNS-related molecular events in living subjects still remain a challenge. Here, we report the development of two activatable 19F magnetic resonance imaging (MRI) molecular probes with different 19F chemical shifts and specific responsive behaviors for simultaneous in vivo detection and deep-tissue imaging of O2•- and ONOO-. These probes are capable of real-time visualization and differentiation of O2•- and ONOO- in living mice with drug-induced acute kidney injury by interference-free multiplexed hot-spot 19F MRI, illustrating the potential of this technique for background-free real-time imaging of diverse biological processes, accurate diagnosis of various diseases in deep tissues, and rapid toxicity evaluation of assorted drugs.

The discovery and large-scale exploration of unconventional oil/gas resources since 1980s have been considered as the most important advancement in the history of petroleum geology. It has not only changed the balance of supply and demand in the global energy market, but also improved our understanding of the formation mechanisms and distribution characteristics of oil/gas reservoirs. However, misconceptions widely exist in studies of different types of petroleum accumulations because of the lack of a unified genetic classification. Unconventional reservoir has been used in the literature as a general name for various oil/gas reservoirs that are formed under complex dynamic mechanisms as long as buoyancy is not the major controlling factor. On the other hand, different terms have been given to the reservoirs even with the same formation mechanism. This paper selected six representative basins in China as the major subject of the study, analyzed the drilling results of 80,762 reservoir layers from 12,237 exploration wells in these basins. By investigating the progress of unconventional oil/gas exploration in North America in the past 30 years and addressing the distribution characteristics of discovered 52,926 oil/gas reservoirs in 1,186 basins around the world, this study revealed the correlations and differences of formation and distribution characteristics between conventional and unconventional oil and gas reservoirs. It was found that there are five correlations between conventional and unconventional reservoirs, including sharing the same oil and gas source, occurring in strata with the same geological age, coexisting in the same sedimentary basins, being confined in the same petroleum systems, and being enriched in the same reservoir layers. It was also found that there are five differences between conventional and unconventional reservoirs, including differences in hydrocarbon compositions, spatial relations to source rocks, reservoir lithology and quality, distribution in geological settings, and reservoir formation mechanism. Then, the unified genetic classification scheme is put forward to clarify their differences and correlations. All kinds of conventional and unconventional oil and gas resource are classified into 3 categories and 6 subcategories according to their dynamic mechanisms of formation, reclassified into 15 types based on main controlling factors, and further divided into 49 styles considering their underground occurrences. The application results show that all different oil/gas reservoirs can find their corresponding positions in the classification scheme, and all the oil/gas reservoirs with the same genetic mechanism, major controlling factor and occurrence can find their particular position in this classification scheme.

Peroxynitrite is an important biomarker for assessing drug-induced liver injury (DILI), which is critical for the development and use of drugs. Herein, we report the development of peroxynitrite-responsive self-assembled 19F MRI nanoprobes, which enable the sensitive imaging of peroxynitrite in L02 cells subjected to oxidative stress and living mice with DILI.

Peroxynitrite (ONOO–) is a highly reactive nitrogen species with potent oxidant and nitrating properties. Its excessive generation can cause DNA and protein damage, thereby contributing to cell injury, and it is closely related to the development of many diseases. Thus, there is an urgent need for a reliable method to determine changes in the steady-state levels of ONOO– in vivo. Ratiometric imaging, due to its built-in self-calibration system, can reduce artifacts and enable reliable in vivo imaging. In this study, we designed and prepared near-infrared (NIR) biomass quantum dots (NI-BQDs) and covalently coupled them with the NIR dye Cyanine7 (Cy7) to construct an NIR dual-emission nanoprobe (NI-BQD-Cy7) for real-time tracing the generation of endogenous ONOO– in single living cells and in vivo by ratiometric fluorescence imaging. NI-BQD-Cy7 exhibited high detection sensitivity and selectivity for ONOO– in the mitochondria. Additionally, it can produce dual NIR fluorescence emission, thus allowing in situ ratiometric fluorescence imaging to real-time trace the generation and concentration changes of ONOO– in vivo. The application of the proposed NIR dual-emission nanoprobe can provide accurate information for the study of the biological function of ONOO– in single living cells and in vivo, and it is very useful to explain the mechanism of cell damage caused by ONOO–.

Superimposed basins are commonly characterized by a complex distribution of oil and gas accumulations. Because they have generally experienced multistage hydrocarbon accumulation and tectonic movement, it is challenging to predict favorable exploration zones in these basins. The exploration of the deep strata of the Sichuan Basin (i.e., a typical superimposed basin), West China, has been unsatisfactory for petroleum prospectors. Therefore, we chose the Cambrian Longwangmiao Formation in the Sichuan Basin as an example to demonstrate the method, i.e., combination of petroleum system elements to quantitatively predict the petroleum favorable exploration zones. Based on the detailed analysis of the hydrocarbon accumulation process, the source rock (S), migration (M), reservoir depositional facies (D), and regional cap rock (C) are the most important elements controlling the formation and distribution of oil and gas accumulations in the studied basin. By studying the functional relationships among these four elements and the distribution of the petroleum accumulations, we determined the accumulation probability related to each element and quantitatively predicted the probability of a favorable hydrocarbon accumulation zone. We built a quantitative model of the reservoir preservation probability based on the statistical relationship between the intensity of the tectonic movement and subsequent destruction of existing oil and gas accumulations. Favorable exploration zones can be determined by overlaying favorable accumulation zones with disturbances associated with the tectonic evolution. The results suggest that the most favorable exploration zones of the Longwangmiao Formation in the Sichuan Basin are distributed in the regions west of Weiyuan and east of Gaoshiti–Moxi, Pengxi–Yilong, and Dazhou–Kaijiang. The production data for existing fields in the Sichuan Basin show that 87% of the successful wells are in the predicted favorable exploration zones and that the success rate with respect to the prediction of failure wells is 67%. This approach highlights the most prospective exploration areas in superimposed basins, which, in general, is challenging and complex for traditional basin modeling tools.

Survivin is widely expressed in tumor tissue, in which the in situ ratiometric fluorescence imaging of intracellular survivin mRNA can provide accurate information for the diagnosis and treatment of cancers, as well as the screening of antitumor drugs. However, the development of a nanoprobe that can be used simultaneously in the diagnosis and treatment of tumors and the screening of antitumor drugs remains a challenge. In an effort to address these requirements, a multifunctional biomass nanoprobe was developed for the photodynamic therapy (PDT) of tumors as well as cancer cell identification and antitumor drug screening based on the ratiometric fluorescence imaging of intracellular survivin mRNA. This nanoprobe was assembled from near-infrared (NIR) biomass quantum dots (BQDs), single-stranded DNA and NIR dye (dylight680) labeled single-stranded DNA. The BQDs contain a large number of chlorophyll molecules, meaning that they can produce a large amount of singlet oxygen under NIR light irradiation, thus realizing the PDT of a tumor. However, the specific binding of the nanoprobe to intracellular survivin mRNA causes the release of dylight680 and reduces the fluorescence resonance energy transfer (FRET) efficiency between the BQDs and dylight680 in the probe, thereby achieving the ratiometric fluorescence imaging of survivin mRNA. Therefore, the prepared nanoprobe can not only be used in the diagnosis of cancers, but also in the targeted PDT of tumors.

Research on shale pore structures has furthered the understanding of shale oil and gas accumulation. However, understanding of mechanisms of shale lithofacies that affect pore structures remains poor, restricting evaluations of marine shale and accurate estimations of gas content. This study focuses on the over-mature Qiongzhusi marine shales in Lower Cambrian of the Southern Sichuan Basin. A series of laboratory experiments were conducted on core samples, including X-ray diffraction (XRD), scanning electron microscopy (SEM), low-pressure gas adsorption (N2 and CO2) and high-pressure mercury intrusion porosimetry (MIP). XRD results show that four main types of shale lithofacies are found in the Qiongzhusi Formation according to the content of siliceous, carbonate and clay minerals, including silica-rich argillaceous shale lithofacies (SAL), argillaceous-rich siliceous shale lithofacies (ASL), carbonate/argillaceous containing siliceous shale lithofacies (C/ASL) and argillaceous/siliceous mixed shale lithofacies (A/SML). SEM images reveal that three kinds of pores within the shale samples (organic matter, intergranular and dissolved pores) with the majority being slit-like and narrow slit-like pores. Silica-rich argillaceous shale lithofacies exhibit the highest pore surface areas and volumes, while other shale lithofacies and carbonate/clay containing siliceous shale lithofacies exhibit relatively lower pore surface areas and volumes. It can be inferred that silica-rich argillaceous shale lithofacies facilitate shale gas storage and flow. Both TOC and clay mineral content are more positively correlated with the microscopic pore structure parameters of micropores than that of mesopores, and thus further interpreted as two dominant factors controlling the development and distribution of micropores. A relatively high quartz content in Qiongzhusi shale of Lower Cambrian are conductive to contribute a large macropore volume, but most importantly, the development of rigid frameworks established by authigenic quartz/pyrite and clay minerals are favorable for the preservation of primary organic matter micropores by providing effective grain supporters. Clay-rich siliceous shale could be deemed as one of the most typical lithofacies types displaying this unique pore-preserving mechanism. Shale lithofacies with different TOC and mineral compositions exhibit distinct differences in pore structures.

A novel oxide material with the formula of Sc2W4O15 and orthorhombic symmetry is synthesized by solid state reactions and its structure, composition, vibrational properties and thermal expansion are investigated and identified by temperature-dependent X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectrometry (EDS), X-ray photoelectron spectrometry (XPS) and dilatometry. It is shown that the oxide material with an orthorhombic symmetry shows a similar structure to that of Sc2W3O12, but with W partially occupying the position of Sc, leading to not only the corner-sharing ScO6–WO4 connections but also the corner-sharing WO6–WO4 connections. Raman spectroscopic studies show that compared to Sc2W3O12, the FWHMs of most Raman modes in Sc2W4O15 increase due to the occupation of W6+ in the Sc3+ position. Besides, the W–O bonds in Sc2W4O15 are slightly harder than those in Sc2W3O12. An intrinsic thermal contraction in a wide range of temperatures (93–572 K) is demonstrated, which is attributed to the librational and translational vibrations of the corner-sharing polyhedra as well as the transverse vibrations of the bridging O atoms in the Sc–O–W and W–O–W linkages.

The crude oils migration and accumulation of the Qionghai (QH) Uplift in the Zhu Ⅲ Super-depression was investigated from the perspective of oil source and migration conduit using gas chromatography-mass spectrometry (GC-MS), stable carbon isotope, quantitative grain fluorescence (QGF) analysis and basin simulation methods. The results on the oil-source correlation showed that oil origins of the five typical reservoirs were very complicated. Crude oils of the eastern and western parts of the QH Uplift were from the Wenchang A sag and the Wenchang B sag, respectively, whereas oil sources of the central part of the QH Uplift were from both the Wenchang A and B sags. The research on the migration conduit showed that structure ridge, fault and connectivity sand body jointly controlled crude oil migration and accumulation in the study area. Under the control of structure ridges and well-connected sand bodies, crude oils accumulated at a low-magnitude folding structure forming the WC13-1, WC13-2 and QH18-1 reservoirs, whereas the sealed fault played an important role in forming the WC8-3 and WC13-6 reservoirs. Combing the differences in oil origins and crude oils migration conduits, we finally identified two types of crude oils migration and accumulation modes from the Wenchang Sag to the QH Uplift. One was a gentle-slope long-distance migration and accumulation model, which was developed from the Wenchang A sag to the QH Uplift. The other was a steep-slope short-distance migration and accumulation model, which was developed from the Wenchang B sag to the QH Uplift. This study could provide guidance for exploring the petroleum potential and prospecting promising zones in the South China Sea.

The well-developed continental shale sequences in the Western Sichuan Depression are characterised by extremely low porosity and permeability, complex lithologies and strong lateral facies changes. The overall lack of proper characterisation of the shale properties has restricted gas exploration and development in the region. In this study, shales from the fifth member of the Xujiahe Formation of the Upper Triassic (T3x5) are comprehensively characterised in terms of their organic geochemistry, mineral composition, microscopic pore structure and gas content. In addition, the influence of various geological factors on the adsorbed gas content is investigated. We proposed a new model for predicting the adsorption gas content of continental shale. The T3x5 shale sequence is found to be rich in organic matter but with variable mineral compositions, pore types and reservoir physical properties. The porosity and permeability of shales are better than those of siltstones and fine sandstones interbedded w...

We experimentally investigate effects of W6+ occupying the sites of Sc3+ in the unit cell of Sc2W3O12 (Sc8W12O48) on the structure, vibration and thermal expansion. The composition and structure of the doped sample (Sc6W2)W12O48 ± δ (with two W6+ occupying two sites of Sc3+ in the unit cell of Sc8W12O48) are analyzed and identified by combining the x-ray photoelectron spectroscopy and the synchronous x-ray diffraction with first-principles calculations based on density functional theory. Results show that the crystal with even W6+ occupying even Sc3+ in the unit cell is stable and maintains the orthorhombic structure at room temperature. The structure of the doped sample is similar to that of Sc2W3O12, and with even W occupying even positions of Sc in the unit cell and constituting the WO6 octahedra. Raman analyses show that the doped sample possesses stronger W–O bonds and wider Raman linewidths than those of Sc2W3O12. The sample doped with W also exhibits intrinsic negative thermal expansion in the measured range of 150 K–650 K.

Carbonate petroliferous basins usually develop fault-reservoir composite migration pathway systems. Accurate estimates of transport efficiency are important for locating oil and gas prospects, which is of considerable interest to oil explorers. The Cambrian Longwangmiao Formation in the Moxi–Gaoshiti area in the Sichuan Basin, the largest single monoblock gas accumulation in China with complicated migration pathway systems, was selected as an example to demonstrate the method. Using a combination of geologic, statistical, experimental data analyses, and quantitative characterization, a quantitative method for calculating the fault-reservoir composite transport efficiency is established for the first time. The results show that fault-reservoir composite migration pathway systems control the hydrocarbon accumulation. The analysis of data from 17 drilling wells using this method indicated a strong correlation between well productivity and composite transport efficiency, and the matching degree of actual and predicted results was as high as 83%. The best locations for oil and gas exploration are near areas with a high composite transport efficiency. Project planners can quickly find oil and gas prospects by matching calculated composite transport efficiencies to observed petroleum occurrences in a basin to avoid costly drilling mistakes. The method will have wide application in other carbonate basins around the world.

The Sinian Dengying Formation is a key target for deep oil and gas exploration in the Sichuan Basin, China. Natural gas was mainly distributed in the Ziyang–Weiyuan area (ZWA) and the Gaoshiti–Moxi area (GMA). At present, the genetic types and sources of natural gas are still unclear and controversial. The chemical composition, stable carbon isotopes, and biomarkers were used to analyze geochemical characteristics, genetic types, and gas–source relations. The results showed that the composition and content of hydrocarbon gas in the ZWA and GMA were similar. Natural gas was a typical dry gas with an average dry coefficient (C1/C1+) of 0.9991, which reflected higher methane (CH4) content and lower heavy hydrocarbon gas (C2+) content. For nonhydrocarbon gas, CO2 (0.01%–26.34%), N2 (0.03%–24.95%), H2S (0.10%–3.19%), and He (0.01%–0.37%) were mainly distributed. Compared with the GMA, the ZWA was characterized by higher N2 content and lower CO2 content. Although the carbon isotopes had not been reversed, the values of δ13C2–δ13C1 were different between the ZWA and GMA, with the GMA having the higher value. The assemblage relation between the natural gas composition and carbon isotopes indicated that the natural gas type was dominated by oil-cracking gas. Mud-shale in the high maturity stage of thermal evolution greatly influenced on the content of N2 and He. H2S mainly belonged to thermochemical sulfate reduction (TSR), and most of CO2 was formed by deep carbonate metamorphism and TSR. The gas–source relation showed that natural gas in the ZWA was derived from the Cambrian Qiongzhusi Formation and that the gas in the GMA mainly originated from the Sinian Dengying Formation and the Cambrian Qiongzhusi Formation. The established hydrocarbon generation model indicated that the Sinian Dengying Formation is potentially gas-rich.

Recent exploration has revealed the great potential of gas resources, complicated gas distributions and geochemical characteristics of natural gases in tight sandstones of the West Sichuan Basin, China (WSBC). The chemical, stable carbon and light hydrocarbon compositions of natural gases from WSBC were investigated to assess the genesis, sources, and migration pattern leading to variations in the geochemical and stable carbon isotope compositions. The analysis shows that the natural gas in the Jurassic tight sandstones occurs as dry gas or wet gas in some places; however, most of the gas in the deep Triassic tight sandstones is apparently dry gas. Carbon isotope distributions increased in the order δ13C1

The study of microscopic pore structures is of central significance to the evaluation of the reservoir quality and well productivity of tight gas sandstone. The second and fourth members (abbreviated as T3x2 and T3x4, respectively) of the Upper Triassic Xujiahe Formation of the Western Sichuan Depression were used as cases to analyze microscopic pore structures and diagenetic controls in consideration of the disparities in reservoir quality and well productivity. Optical microscopy of thin sections, Micro-CT Scanning, scanning electron microscopy (SEM), High Pressure Mercury Injection (HPMI) and apex methods based on the HPMI results were used to determine the pore and throat geometries and the types and pore size distributions in terms of the quantity and levels of pore connectivity. Tight sandstone reservoirs of the study area are characterized by poor physical properties, with the T3x2 reservoirs presenting relatively higher levels of permeability and lower porosity levels than those of the T3x4 reservoirs. The pore spacing configurations, sizes and distributions and throat geometries reveal significant disparities. Primary pores and micro-fractures were found to be more developed in the T3x2 reservoirs with bending and narrow pore throats measured as smaller than 0.5 μm. Compared to those of the T3x2 reservoirs, secondary pores including moldic and intracrystalline pores were more developed in the T3x4 reservoirs with relatively larger, straighter and wider throats of 0.5–1.0 μm. An evaluation of the pore connectivity levels shows that only 26.86% and 28.90% pores are closely connected to the whole for T3x2 and T3x4 reservoirs, respectively. Four major diagenetic processes were found to control reservoir quality and the microscopic pore structure. Mechanical compaction is the primary cause of the densification of reservoirs in the study area. Compared to that observed in the T3x4 reservoirs, more intensive mechanical compaction was observed in the T3x2 reservoirs, changing the configuration of the throats present, reducing the pore throat radii, and ultimately lowering the porosity of T3x2 reservoirs as a whole. Quartz overgrowth and late period carbonate cements were observed in partly filled pore spaces, narrowing throats and reducing pore connectivity, but eogenetic cementation and chlorite cements can increase the pressure-resistance of sandstone and inhibit compaction quartz overgrowth. Thus, T3x4 reservoirs are relatively more porous as a result of eogenetic calcite cementation, and primary pores are more developed in T3x2 reservoirs with chlorite cements. Dissolution is a major factor that improves the tight sandstone reservoir quality because it generates a large volume of secondary pores. The more intensive levels of dissolution in T3x4 reservoirs not only creates more intergranular, intragranular, moldic and intracrystalline pores but also further increases the porosity of T3x4 reservoirs. Fracturing effects have developed in the study area to improve pore connectivity levels and thus the permeability of tight sandstone reservoirs, potentially explaining the pore connectivity and permeability of certain T3x2 reservoirs. This work may be able to be used as a useful reference for the reservoir quality evaluation and exploration of tight gas sandstone reservoirs for similar oil fields worldwide.

Pyrite is the most common authigenic mineral preserved in many ancient sedimentary rocks. Pyrite also widely exists in the Longmaxi and Wufeng marine shales in the middle Yangtze area in South China. The Longmaxi and Wufeng shales were mainly discovered with 3 types of pyrites: pyrite framboids, euhedral pyrites and infilled framboids. Euhedral pyrites (Py4) and infilled framboids (Py5) belong to the diagenetic pyrites. Based on the formation mechanism of pyrites, the pyrites could be divided into syngenetic pyrites, early diagenetic pyrites, and late diagenetic pyrites. Under a scanning electron microscope (SEM), the syngenetic pyrites are mostly small framboids composed of small microcrystals, but the diagenetic pyrites are variable in shapes and the diagenetic framboids are variable in sizes with large microcrystals. Due to the deep burial stage, the pore space in the sediment was sharply reduced and the diameter of the late diagenetic framboids that formed in the pore space is similar to the diameter of the syngenetic framboids. However, the diameter of the syngenetic framboid microcrystals is suggested to range mainly from 0.3 &micro, m to 0.4 &micro, m, and that of the diagenetic framboid microcrystals is larger than 0.4 &micro, m in the study area. According to the diameter of the pyrite framboids (D) and the diameter of the framboid microcrystals (d), the pyrite framboids could be divided into 3 sizes: syngenetic framboids (Py1, D &lt, 5 &micro, m, d &le, 0.4 &micro, m), early diagenetic framboids (Py2, D &gt, m, d &gt, m) and late diagenetic framboids (Py3, D &lt, m). Additionally, the mean size and standard deviation/skewness values of the populations of pyrite framboids were used to distinguish the paleoredox conditions during the sedimentary stage. In the study area, most of the pyrite framboids are smaller than 5 &micro, m, indicating the sedimentary water body was a euxinic environment. However, pyrite framboids larger than 5 &micro, m in the shales indicated that the sedimentary water body transformed to an oxic-dysoxic environment with relatively low total organic carbon (TOC: 0.4&ndash, 0.99%). Furthermore, the size of the framboid microcrystals could be used to estimate the gas content due to thermochemical sulfate reduction (TSR). The process of TSR occurs with oxidation of organic matter (OM) and depletes the H bond of the OM, which will influence the amount of alkane gas produced from the organic matter during the thermal evolution. Thus, syngenetic pyrites (d ranges from 0.35 &micro, m to 0.37 &micro, m) occupy the main proportion of pyrites in the Wufeng shales with high gas content (1.30&ndash, 2.30 m3/t), but the Longmaxi shales (d ranges from 0.35 &micro, m to 0.72 &micro, m) with a relatively low gas content (0.07&ndash, 0.93 m3/t) contain diagenetic pyrites. Because of TSR, the increasing size of the microcrystals may result in an increase in the value of &delta, 13C1 and a decrease in the value of &delta, 13C1-&delta, 13C2. Consequently, the size of pyrite framboids and microcrystals could be widely used for rapid evaluation of the paleoredox conditions and the gas content in shales.

An unconventional, continuous petroleum system consists of an accumulation of hydrocarbons that is found in low-matrix-permeability rocks and contain large amounts of hydrocarbons. Tight-sand gas in the Jurassic and shale gas within the fifth member of Xujiahe Formation (T3x5) are currently regarded as the most prolific emerging unconventional gas plays in China. The conventional and systematical evaluation of T3x5 source rocks was carried out for the first time in the western Sichuan basin (WSD). Hydrocarbon generation and expulsion characteristics (including intensity, efficiency, and amount) of T3x5 source rocks were investigated. Results show that T3x5 source rocks are thick (generally >200 m), have high total organic content (TOC, ranging from 2.5 to 4.5 wt%), and dominated by III-type kerogen. These favorable characteristics result in a great hydrocarbon generating potential under the high thermal evolution history (R o > 1.2%) of the area. An improved hydrocarbon generation potential methodology was applied to well data from the area to unravel the hydrocarbon generation and expulsion characteristics of T3x5 source rocks in the WSD. Results indicate that the source rocks reached hydrocarbon expulsion threshold at 1.06% R o and the comprehensive hydrocarbon expulsion efficiency was about 60%. The amount of generation and expulsion from T3x5 source rocks was 3.14 × 1010 and 1.86 × 1010 t, respectively, with a residual amount of 1.28 × 1010 t within the source rocks. Continuous-type tight-sand gas was predicted to develop in the Jurassic in the Chengdu Sag of the WSD because of the good source-reservoir configuration (i.e., the hydrocarbon generation and expulsion center was located in Chengdu Sag), the Jurassic sandstone reservoirs were tight, and the gas expelled from the T3x5 source rocks migrated for very short distances vertically and horizontally. The amount of gas accumulation in the Jurassic reservoirs derived from T3x5 source rocks is up to 9.3 × 108 t. The T3x5 gas shale has good accumulation potential compared with several active US shale-gas plays. Volumetrically, the geological resource of shale gas is up to 1.05 × 1010 t. Small differences between the amounts calculated by volumetric method compared with that by hydrocarbon generation potential methodology may be due to other gas accumulations present within interbedded sands associated with the gas shales.

A great difference exists between the hydrocarbon charging characteristics of different Tertiary lacustrine turbidites in the Jiyang Super-depression of the Bohai Bay Basin, east China. Based on wireline log data, core observation and thin-section analyses, this study presents detailed reservoir property data and their controlling effects from several case studies and discusses the geological factors that govern the hydrocarbon accumulation in turbidite reservoirs. The lacustrine fluxoturbidite bodies investigated are typically distributed in an area of 0.5–10 km2, with a thickness of 5–20 m. The sandstones of the Tertiary turbidites in the Jiyang Super-depression have been strongly altered diagenetically by mechanical compaction, cementation and mineral dissolution. The effect of compaction caused the porosity to decrease drastically with the burial depths, especially during the early diagenesis when the porosity was reduced by over 15%. The effect of cementation and mineral dissolution during the late-stage diagenesis is dominated by carbonate cementation in sandstones. High carbonate cement content is usually associated with low porosity and permeability. Carbonate dissolution (secondary porosity zone) and primary calcite dissolution is believed to be related to thermal maturation of organic matter and clay mineral reactions in the surrounding shales and mudstone. Two stages of carbonate cementation were identified: the precipitation from pore-water during sedimentation and secondary precipitation in sandstones from the organic acid-dissolved carbonate minerals from source rocks. Petrophysical properties have controlled hydrocarbon accumulation in turbidite sandstones: high porosity and permeability sandstones have high oil saturation and are excellent producing reservoirs. It is also noticed that interstitial matter content affects the oil-bearing property to some degree. There are three essential elements for high oil-bearing turbidite reservoirs: excellent pore types, low carbonate cement ( 15% and average permeability >10 mD.

The chemical compositions of crude oils from over 20 oilfields in the Zhanhua Depression, Bohai Bay Basin, were studied in order to understand their genetic relationships, thermal maturity and biodegradation ranking. Molecular geochemical parameters indicate the presence of three possible oil families in reservoirs ranging from Paleozoic (basement) to Neogene. A number of biomarker features support deposition of the source rocks for these oils under a wide range of depositional environments. The majority of the oils discovered in the depression belong to the FL family, and display characteristics consistent with a dominantly freshwater (to slightly brackish water) lacustrine source rock in the Es 3 member of the Shahejie Formation. The somewhat geographically restricted SL family oils are apparently linked to saline lacustrine, carbonate-evaporite source rocks distributed mostly in the upper Es 4 member of the Shahejie Formation from the Bonan-Gubei sag areas. The thermally less mature BL family oils occur mostly within the Es 1 , Es 2 or Dongying Formation reservoirs near the central sag areas, and show close affinities to the interbedded or intercalating Es 1 calcareous mudstones and oil shales deposited in a slightly saline to dominantly brackish water lacustrine setting. The SL and FL family oils are generally mature, whereas most of the BL family oils usually show low maturity. Oil-source correlation demonstrates strong genetic relationships between the mature Es 4 and Es 3 source rocks of the Eocene–Oligocene Shahejie formation in the sag areas and the oils accumulated in the shallow Neogene petroleum plays. The geochemical data provide strong support for two sharply contrasting hydrocarbon migration scenarios: (1) short distance lateral migration is dominant in the central sag areas; and (2) the fault-fracture mesh facilitated vertical migration, and coupled with the regional porous Guantao Formation sand sheets, makes the structural, stratigraphic and lithological features over basement high blocks the focal points for petroleum accumulation. Therefore, further exploration in this highly mature petroleum province should focus on heavy oils in the shallow Neogene strata and light oils in the tight sandstones of the deep sag areas.