Enrichment Of Hydrocarbons Research Articles

Pore Structure, Fractal Features, and Oil Content Evaluation of Lacustrine Shale: A Case Study of First Member of Paleogene Shahejie Formation, NE China

The complex and heterogeneous pore structure and oil content of lacustrine shales introduce significant challenges in the exploration of shale petroleum systems. To further expand our geological understanding of lacustrine shales and provide guidance for hydrocarbon exploration, in this study, based on programmed and improved Rock-Eval pyrolysis, total organic content (TOC) measurements, scanning electron microscopy (SEM) observations, and N2 adsorption (NA) experiments, a systematic evaluation of the mineral composition, geochemical features, pore structure, and oil contents of the third member of the Paleogene Shahejie Formation (Es3) shale in the typical lacustrine hydrocarbon enrichment sag (Nanpu Sag, Bohai Bay Basin) is conducted. The fractal theory is selected to quantify the pore system’s heterogeneity; also, the relationships between the pore structure parameters and the oil contents and mineral composition are revealed. Our results reveal the geochemical features of the Es3 shale are excellent, and thus, they can be classified as a set of high-quality source rocks (average TOC of 4.2%, mainly type II kerogen, and in the mature stage). Based on the SEM and NA analyses, the intercrystalline pores dominate the pore system. Moreover, the mesopores contribute the most specific surface area (SA) and pore volume (PV) to the samples (average contribution rates of 74.7 and 75.0%, respectively). The fractal dimensions have relatively strong positive correlations with PV and SA, which means more heterogeneous and complex pore structures provide more storage space and adsorption sites for shale oil accumulation. The clay mineral content is the most important factor which controls the pore structure parameter, and high clay content indicates high SA and PV. According to proposed numerical movable and adsorption hydrocarbon calculation models, the TOC content is the dominant factor controlling the movable and adsorption oil contents, but other factors’ impact also cannot be ignored. Our study not only provides guidance for shale oil exploration in the study area but also broadens our understanding of the oil contents of lacustrine shale.

Analysis of tight oil accumulation conditions and prediction of sweet spots in Ordos Basin: A case study

Tight sandstone reservoirs are widely developed in the Mesozoic Yanchang Formation of the Ordos Basin, China. There is a lack of understanding on the sedimentary setting, source-reservoir relationship and oil accumulation conditions in this area. In this study, through the comprehensive analysis of the distribution of tight oil, we evaluated the properties and petrological features of reservoir, geochemical characteristics of source rocks, the source-reservoir relationship, as well as the trapping, preservation and accumulation conditions of tight oil in the Chang 7 Member, and predicted the sweet spots of tight oil in the study area. The results show that the Chang 7 Member is a typical low-porosity and ultra-low permeability reservoir with great tightness, small pore throat and high capillary pressure, and must have been of near-source accumulation. The source rocks are mainly developed in the Chang 73 submember, and the reservoirs mainly occur in the Chang 71 and Chang 72 submembers, forming a combination mode of “lower source rock and upper reservoir”. Sandbodies with good connectivity and fractures being well developed in local areas are the main hydrocarbon transport systems. The abnormal high pressure caused by hydrocarbon generation and pressurization is the main driving force of tight oil accumulation. The mode of hydrocarbon transportation is dominated by the vertical or lateral migration from underlying source rocks or adjacent source rocks to reservoirs within a short distance. Following the integrated evaluation of lithology, physical properties and oil saturation of reservoirs and geochemical characteristics of source rocks, we grouped the sweet spots of Chang 7 Member into three types: Type I, Type II and Type III. Among others, the Type I sweet spots are the best in terms of porosity, permeability and source rock thickness and hydrocarbon enrichment which should be the focus of oilfield development. This study lays an important foundation for the economic and efficient development of tight oil in the Chang 7 Member of Heshui area, and has important implications on tight sandstone reservoirs in other regions of Ordos Basin in China.

Variability and Main Controlling Factors of Hydrocarbon Migration and Accumulation in the Lower Paleozoic Carbonate Rocks of the Tazhong Uplift, the Tarim Basin, Northwest China

Hydrocarbon migration patterns and pathways were studied on the basis of three-dimensional seismic interpretation, drilling, geochemistry, production performance, and other data. Using these findings, the main factors controlling hydrocarbon migration and accumulation in the Lower Paleozoic carbonate rocks of the Tazhong Uplift were discussed. The spatiotemporal relationship between the hydrocarbon kitchens and pathway systems of the Tazhong Uplift and the spatial pattern of pathway systems were considered the main factors causing differences in hydrocarbon enrichment. Results also revealed that the Lower Paleozoic carbonates of the Tazhong Uplift have two hydrocarbon accumulation systems (inside and outside the source rocks). For the accumulation system within the source rocks, hydrocarbon migration and enrichment are vertically differentiated. Middle Cambrian gypsum salt rocks serve as the boundary, above which thrust and strike-slip faults mainly allow vertical transport of hydrocarbons. A multistage superposition pattern of strike-slip faults controls the differences in hydrocarbon enrichment on the periphery of the fault zone. Beneath the gypsum-salt rocks, hydrocarbon migration and enrichment is controlled by the topography of paleostructures and paleogeomorphology. For the hydrocarbon accumulation system outside the source rocks, hydrocarbon migration and enrichment are restricted by the layered pathway system, and the topography of the paleostructures and paleogeomorphology is the key factor controlling hydrocarbon enrichment. The Tazhong No. 1 Fault is the main vertical pathway system in the area underlain by no source rocks, and hydrocarbons are enriched at the periphery of the Middle-Lower Cambrian and No. 1 Fault Zone.

Influence of a Paleosedimentary Environment on Shale Oil Enrichment: A Case Study on the Shahejie Formation of Raoyang Sag, Bohai Bay Basin, China

The characteristics of paleosedimentary environments are of great significance for the enrichment of organic matter (OM) and hydrocarbons in lacustrine shale. This study analyzed mineralogy, well logging data, organic geochemical parameters (total organic carbon and pyrolyzed hydrocarbon), inorganic geochemical parameters (major and trace elements), and multiple geochemical proxies based on inorganic geochemical parameters. These were used to reconstruct the paleosedimentary environment of the lower 1st Member of the Shahejie Formation (Es1L) to reveal OM and shale oil enrichment mechanisms and establish a shale oil enrichment model. The (Fe2O3+Al2O3)/(CaO + MgO), Sr/Ba, Rb/Sr, Cu/Al, and Th/U parameters indicate that the Es1L in Raoyang Sag was deposited in a paleoenvironment dominated by arid paleoclimate, reducing conditions, and saltwater. Paleoclimate, clastic influx intensity, preservation conditions, paleoproductivity, and paleosalinity all affect OM abundance. The OM accumulation in the shale of Es1L was mainly controlled by the high primary productivity of surface water due to algal blooms and moderate salinities, which was achieved using stratified water columns with low oxygen conditions in bottom water. As the main valuable sites for shale oil storage, carbonate mineral depositions are of great significance for oil enrichment. As the dominant lithofacies for oil enrichment, carbonate-rich shale and calcareous shale lithofacies were deposited under a drier paleoclimate, low clastic influx intensity, strong reducing conditions, high paleoproductivity, and moderate salinity paleoenvironment. Additionally, the profile of the shale oil sweet spot was determined through the combination of lithofacies, logging, and paleosedimentary environment data.

Breakthrough of natural gas exploration in the beach facies porous dolomite reservoir of Middle Permian Maokou Formation in the Sichuan Basin and its implications: A case study of the tridimensional exploration of Well JT1 in the central-northern Sichuan Basin

The neritic carbonate reservoir of Middle Permian Maokou Formation in the Sichuan Basin has been always treated as a fractured and fractured-vuggy reservoir. After realizing the breakthrough of natural gas exploration in the Lower Cambrian Canglangpu Formation in the Taihe gas bearing area of central-northern Sichuan Basin, Well JT1, a wildcat well, recently discovers a beach facies porous dolomite reservoir in the Maokou Formation above the Canglangpu Formation, and the high-yield industrial gas flow of 112.8 × 104 m3/d is obtained during the test. And thus, Well JT1 achieves the breakthrough of tridimensional natural gas exploration in multiple gas bearing series of strata in the vertical direction and realizes the new discovery of reservoir type in the Maokou Formation. In order to further clarify the characteristics and control factors of the beach facies porous dolomite reservoir of Maokou Formation in the Taihe gas bearing area, this paper studied its sedimentary evolution, high-energy beach facies characteristics, reservoir characteristics and following natural gas exploration direction. And the following research results were obtained. First, along the syneclise margin of central-northern Sichuan Basin develops a beach facies porous reservoir of the second Member of Maokou Formation, whose lithology is dominated by residual dolarenite and calcsparite calcarenite and reservoir space is mainly acted by intergranular pores and intercrystalline pores, with the average porosity of 4.9%. Second, in the middle and late stage of Maokou period, Guangyuan-Bazhong paleo faulted depression was developed in the northern Sichuan Basin and intraplatform low was developed in the central-northern Sichuan Basin. In the central and the northern Sichuan Basin, the high-energy beach of Maokou Formation is distributed around the faulted depression and the syneclise margin in a large scale, and the paleogeographic pattern of “one-margin and three-high belt” is presented. Third, under the control of high-energy beach facies, the Maokou Formation porous reservoir in the central-northern Sichuan Basin is distributed along the “one-margin and three-high belt” in a large scale. The high-energy beach facies of “one-margin and three-high belt” covers the area of 6500 km2. In this area, multiple sets of source rocks (Cambrian, Silurian and Permian) are developed vertically, hydrocarbon source fault is developed and carrier system is good, which is favorable for the large-scale hydrocarbon enrichment and accumulation. In conclusion, there are geological conditions for the development of facies controlled porous reservoir in the Maokou Formation of the Sichuan Basin, and the “one-margin and three-high belt” is the favorable area for the exploration of beach facies porous dolomite reservoir. The research results point out the new exploration field and direction for the large-scale increase of natural gas reserves in the Sichuan Basin.

Hydrophobic polymer tethered magnetic zirconium-based metal-organic framework as advance and recyclable adsorbent for microwave-assisted extraction of polycyclic aromatic hydrocarbons from environmental water samples

Hydrophobic poly (glycidyl methacrylate) tethered magnetic amino-functional zirconium metal-organic framework (UiO-66-NH2) was fabricated for the first time for rapid microwave-assisted magnetic solid-phase extraction of trace polycyclic aromatic hydrocarbons from environmental water samples. UiO-66-NH2 endowed the nanocomposite with remarkable specific surface area (175.2 m2/g) and short diffusion route, while poly (glycidyl methacrylate) provided hydrophobic interaction towards hydrophobic polycyclic aromatic hydrocarbons, both of which contributed to the satisfactory extraction performance. The successful preparation of the nanocomposite was confirmed by transmission electronic microscopy, scanning electron microscopy, Fourier transform infrared spectroscopy, N2 adsorption-desorption experiment, powder X-ray diffraction patterns, contact angle measurement and vibrating sample magnetometry. In addition, an optimized protocol for microwave-assisted magnetic solid-phase extraction was carried out, including adsorbent amount (20–160 mg), adsorption time (30–150 s), desorption time (10–80 s) and desorption solvents (methanol, acetonitrile, acetone and ethyl acetate). Under the most favorable conditions, the microwave-assisted method afforded magnetic solid-phase extraction with short extraction time (1 min), a wide linear response (1.56–200 μg/L), good linearity (R2 ≥ 97.83%), low limits of detection (0.04–4.68 μg/L) and good precision (RSD ≤ 6.39%) for six polycyclic aromatic hydrocarbons. The proposed method was successfully applied in analysis of real water samples with mean recoveries in the range of 82.6–118.4% at three spiked levels and the relative standard deviations less than 10.7%. The results indicated that our developed method had great potential in enrichment and detection of trace polycyclic aromatic hydrocarbons in real aqueous samples.

A thin‐layer solid‐phase extraction–liquid film elution technique used for the enrichment of polycyclic aromatic hydrocarbons in water

In this article, we propose a novel microsolid-phase extraction and elution technique, which we called the thin-layer solid-phase extraction-liquid film elution technique. The thin-layer solid-phase extraction phase is an octadecylsilylated sol gel- coated porous silica thin film prepared on the outer wall of a test tube, which has a larger surface area for the extraction of the target compounds compared to a conventional solid-phase microextraction phase. After optimization of the extraction procedure for five types of polycyclic aromatic hydrocarbons, the liquid film elution technique was investigated. Liquid film elution is an elution technique wherein the compounds extracted into the thin-layer solid-phase extraction phase are eluted using a small volume of solvent film formed around the extraction phase. The results show that the elution can be carried out using 150 μL of eluent. Enrichment factors between 20 and 34 were obtained for polycyclic aromatic hydrocarbons containing more than four aromatic rings in 10mL aliquots of aqueous samples. Finally, recoveries of 85-112% were obtained for polycyclic aromatic hydrocarbons containing more than four aromatic rings from spiked natural water samples using the thin-layer solid-phase extraction-liquid film elution technique.

Hydrocarbon Enrichment and Main Controlling Factors in Offshore Rift Basins of China: A Case Study in the Beibuwan Basin

AbstractBeibuwan Basin is an important offshore oil and gas bearing basin of China. However, the distribution of oil and gas in different sags is uneven, and the rule of hydrocarbon accumulation and main controlling factors have not been clearly understood in this basin. Based on abundant seismic, well and analytical data, the differences and main controlling of tectonic evolution, sedimentary filling and source rock quality in sags are analyzed, and combined with the study of geothermal filed, the main controlling factors of differential hydrocarbon generation in sags of the Beibuwan Basin are clarified. On the basis of the research above, the hydrocarbon enrichment of the basin is clarified through the systematic analysis of reservoir‐caprock assemblage and accumulation characteristics of different structural units. The results show that there are four NE‐trending sag zones in the basin, and under the influence of fault activity, the scale of sags is regularly distributed. The scale of rifts in different sag zones decreases gradually from northwest to southeast and the scale of rifts in the middle of a single sag zone is normally larger than that at two ends. Under the control of the sag‐controlling faults activity, paleoproductivity and organic matter preservation conditions, the quality of source rocks in sags of the Beibuwan Basin decreases from northwest to southeast. The hydrocarbon‐rich sags in the Beibuwan Basin were formed under the control of source rocks and geothermal field, and the distribution of large‐medium scale fields is controlled by the favorable structural traps in the rift strata of inner gentle slope zone. The understanding of the hydrocarbon enrichment and main controlling factors in the Beibuwan Basin also provides a significant guidance for the oil and gas exploration in other rift basins.

Discovery of carbonate source rock gas reservoir and its petroleum geological implications: A case study of the gas reservoir in the first member of Middle Permian Maokou Formation in the Fuling area, Sichuan Basin

Carbonate rocks in the first member of the Middle Permian Maokou Formation in the Sichuan Basin (hereinafter “Mao 1 Member” for short) have been taken as a set of carbonate source rocks, and they have not been specifically studied from the aspects of reservoir evaluation and testing. By referring the exploration ideas of unconventional natural gas, the Mao 1 Member in Fuling area of southeastern Sichuan Basin has obtained industrial gas flow in development wells in recent years. In order to further clarify the natural gas exploration potential of the Mao 1 Member in this area, it is necessary to study its sedimentary characteristics, natural gas accumulation conditions and main control factors based on the data of field section measurement, systematic coring in drilling and laboratory testing. The following research results were obtained. First, the gas reservoir in the Mao 1 Member in the Fuling area is of source–reservoir integration, and its natural gas is mainly enriched in blackish gray marlite and nodular marlite. Second, its reservoir spaces are dominated by grain margin pores (fractures), diagenetic shrinkage pores (fractures), organic pores and fractures. Third, the pores are mostly in nanometer scale, and the main pore diameter is in the range of 5–50 nm, which is between shale reservoir and conventional reservoir, with strong heterogeneity. Fourth, the gas reservoir is characterized by source–reservoir coexistence, lithology controlling reservoir and extensive layered distribution, presenting two-stage differential hydrocarbon enrichment, namely intraformational near-source enrichment in the early stage and interformational blowdown adjustment in the late stage. Fifth, the development of blackish gray organic-rich fine marlite which is deposited with the episodic upwelling in the outer ramp facies belt is the foundation for the natural gas accumulation, the transformation of clay minerals controls the development of higher-quality reservoirs, good preservation conditions are the key to the natural gas accumulation, and fracture development is favorable for the enrichment and high yield of natural gas. In conclusion, the Mao 1 Member in this area is a special type of gas reservoir, i.e., carbonate source rock gas reservoir, which has greater potential of natural gas exploration and industrial gas flow have been obtained in several wells. The discovery of such type of gas reservoirs not only expands the domain of natural gas exploration in the Sichuan Basin, but provides the reference for the natural gas exploration in other areas of South China.

Differential hydrocarbon enrichment in deep Paleogene tight sandstones of the Dongpu Depression in Eastern China

To clarify the characteristics and enrichment rules of Paleogene tight sandstone reservoirs inside the rifted-basin of Eastern China, the third member of Shahejie Formation (abbreviated as Es3) in Wendong area of Dongpu Depression is selected as the research object. It not only clarified the geochemical characteristics of oil and natural gas in the Es3 of Wendong area through testing and analysis of crude oil biomarkers, natural gas components and carbon isotopes, etc.; but also compared and explained the types and geneses of oil and gas reservoirs in slope zone and sub-sag zone by matching relationship between the porosity evolution of tight reservoirs and the charging process of hydrocarbons. Significant differences have been found between the properties and the enrichment rules of hydrocarbon reservoirs in different structural areas in Wendong area. The study shows that the Paleogene hydrocarbon resources are quasi-continuous distribution in Wendong area. The late kerogen pyrolysis gas, light crude oil, medium crude oil, oil-cracked gas and the early kerogen pyrolysis gas are distributed in a semicircle successively, from the center of sub-sag zone to the uplift belt, that is the result of two discontinuous hydrocarbon charging. Among them, the slope zone is dominated by early conventional filling of oil-gas mixture (at the late deposition period of Dongying Formation, about 31–27 Ma ago), while the reservoirs are gradually densified in the late stage without large-scale hydrocarbon charging (since the deposition stage of Minghuazhen Formation, about 6–0 Ma). In contrast, the sub-sag zone is lack of oil reservoirs, but a lot of late kerogen pyrolysis gas reservoirs are enriched, and the reservoir densification and hydrocarbon filling occur in both early and late stages.

Main controlling factors for the enrichment of shale oil and significant discovery in second member of Paleogene Funing Formation, Qintong Sag, Subei Basin

Based on the study of hydrocarbon generation features, oil bearing property and reservoir property of shale in the second member of Paleogene Funing Formation in the Qintong Sag of the Subei Basin, the main controlling factors of shale oil enrichment were analyzed. Shale of the second member of Funing Formation in the Qintong Sag was featured by large-scale thickness and medium TOC content, which provided a material basis for shale oil enrichment. The vitrinite reflectance (%Ro) of shale in the second member of Funing Formation in the deep sag distributed between 0.9%-1.0%, indicating a moderate thermal evolution degree. Shale oil has the characteristics of light hydrocarbon, high gas-measured total hydrocarbon value and good fluidity. Few faults were developed, resulting in good preservation conditions and high formation pressure, which were conducive to hydrocarbon enrichment. High content of brittle minerals and well-developed lamella and natural fractures made formation fracturing easier. The continuous and large-area distribution of high-quality shale is the basis for oil and gas abundance. Preservation condition is the key factor to reservoir formation. The degree of evolution is a decisive factor of oil-bearing. High pressure, lamina development and high brittle mineral content are important factors for high yield. The shale oil in second member of Funing Formation in Shaduo area has the characteristics of low TOC content (1%), low gas oil ratio (40-80 m3/t) and high pressure (1.25 MPa). The success of this well has reduced the shale oil evaluation standard and threshold, and expanded the development space of shale oil.

Characteristics of the Cretaceous Magmatism in Huanghua Depression and Their Relationships with Hydrocarbon Enrichment

The Huanghua depression located in the hinterland of the Bohai Bay Basin in eastern China is a typical area for the research of multistage magmatic activities with hydrocarbon enrichment, many high-yield wells related to igneous rocks were discovered within the Cretaceous strata in recent years. However, the spatial and temporal distribution of Cretaceous igneous rocks remains unclear, and the relationships among magmatic sequence, lithology, and hydrocarbon enrichment have been poorly studied. In order to solve these problems, core observation, logging analysis, major element analysis, zircon U-Pb chronology, oil-bearing grade statistics and reservoir spaces analysis were used to subdivide the magmatism cycles and to investigate the characteristics of igneous reservoirs. Our results show that the Mesozoic magmatism in Huanghua depression started in 140.1±1.4 Ma and could be divided into two stages including the Early Cretaceous stage and Late Cretaceous stage. The Early Cretaceous magmatism principally developed basic-intermediate rocks in the north zone, and could be subdivided into 3 cycles with their forming ages of 140, 125–119, and 118–111 Ma, respectively. By contrast, the late stage mainly developed intermediate-acid rocks centralized in the south zone and formed at 75–70 Ma. The GR and SP curves are good indicators for the contrast of different lithologies, lithofacies and for magmatic sequences division. Intensive magmatism may have an advantage to form reservoirs, since basalt in cycle III in the Early Cretaceous and dacite porphyrite in the Late Cretaceous have great exploration potential. Lithology and tectonic fractures have an important influence on the formation of reservoir spaces and hydrocarbon enrichment. The characteristics of Cretaceous magmatism and igneous reservoirs in Huanghua depression and adjacent areas are summarized, providing important information for igneous reservoirs research and oil-gas exploration in the Cretaceous in related areas.

Synthesis of graphitic carbon nitride on 3D porous anodized aluminum wire as new fiber for microextraction of polycyclic aromatic hydrocarbons in water and wastewater samples

ABSTRACT A simple, fast, and sensitive solid phase microextraction method (SPME) has been applied for the enrichment and simultaneous determination of trace and toxic polycyclic aromatic hydrocarbons in water and wastewater samples. This method is based on the adsorption of these volatile compounds on a new robust fiber built from anodized aluminum wire coated with g-C3N4. Extraction of the analytes from different matrices on the fiber surface was performed by headspace mode (HS-SPME) at optimized conditions. This proposed method was used to determine trace amounts of some polycyclic aromatic hydrocarbons (PAHs) in real water and wastewater samples and provided good repeatability with a low limit of detection (LOD).

Bacteria from black crusts on stone monuments can precipitate CaCO3 allowing the development of a new bio-consolidation protocol for ornamental stone

The microbial precipitation of CaCO3 is an emerging strategy for the consolidation of decayed limestone. Strains of Bacillus sp. and Micrococcus sp. isolated from black crusts were selected by polycyclic aromatic hydrocarbon enrichment culture and tested for their ability to precipitate CaCO3 by induced mineralization. Among the isolates, Bacillus sp. A2, B1, B5 and Micrococcus sp. A10 produced the largest quantities of biogenic calcite. Stone bio-consolidation was then tested using Carbogel as a carrier. The most efficient bio-cementation on limestone slabs was achieved by Bacillus sp. A2 and B1 and Micrococcus sp. A10. Bio-consolidation treatments were also applied to fragmented stones from the Church of Santa Maria dei Miracoli by inoculating the three bacterial strains individually or as a mixture. Bacillus sp. A2, Micrococcus sp. A10 and the mixture achieved the most efficient consolidation. Our data showed that Carbogel provides an appropriate substitute for natural biofilm formation in bio-consolidation protocols. Scanning electron microscopy and energy-dispersive X-ray spectroscopy revealed calcified bacterial cells filling the pores of stone specimens, increasing the calcium content by 100% more than a non-inoculated control treatment under the same conditions. Our new bio-consolidation protocol therefore provides an effective strategy to prevent the further deterioration of stone monuments.

Effects of petroleum retention and migration within the Triassic Chang 7 Member of the Ordos Basin, China

The effects of petroleum retention within and expulsion from five intervals within the Triassic Chang 7 Member in the Ordos Basin in China have been demonstrated by deciphering a large suite of petrologic, organic petrographic, and organic geochemical analyses on 106 core samples.Organic properties and lithological heterogeneities control the amount and chemical composition of retained petroleum. Enrichment of aliphatic hydrocarbons in the silty, organic-lean intervals versus enrichment of aromatic fluids in the clayey, organic-rich units are probably caused by compositional fractionation occurred during primary and short-distance secondary migration. Migration of excess petroleum from organic-rich units to those organic-lean counterparts was further corroborated by the negative expulsion efficiencies calculated using a mass-balance model in the organic-lean intervals. Capillary pressure difference induced by the contrast in pore throat size of the clayey, organic-rich versus the silty, organic-lean intervals is postulated to be the major driver for the migration.A significant implication of this study is that the hydrocarbons in the first and fourth intervals constitute potential petroleum exploitation targets, given (i) improved oil quality caused by enriched aliphatic compounds versus viscous aromatic and polar compounds, (ii) lower organic matter sorption affinities, (iii) relatively high contents of brittle minerals in these two intervals. Despite its high content of retained hydrocarbons, the organic-rich fifth interval is not the best target, which is mainly due to the high sorption affinity of the organic matter structure, thereby causing low oil mobility and producibility.

The hydrocarbon accumulation potential of Upper Cretaceous to Paleogene in the northern Kaikang trough, Muglad Basin

This paper investigates the characteristics of sedimentary faces, source rocks, and hydrocarbon accumulation in detail within the Paleogene and Upper Cretaceous in the northern Kaikang trough, Muglad Basin. Analysis shows that the fluvial floodplain, delta, and shore-shallow lake facies are well developed in the main formations and several reservoir-cap assemblages are formed. Research on geochemical indicators, hydrocarbon generation, and expulsion potential of source rocks indicated that the thickness of good source rocks in Paleogene ranges from 50 to 200 m and TOC value can reach 0.5–1.3%, but it is immature and has no hydrocarbon generation potential. Nevertheless, the Upper Cretaceous source rocks are mostly matured, but its hydrocarbon generation is limited because of lower TOC (only 0.5–0.8%) and thinner thickness (only 10 m). The main effective source rock is the AG Group in the Lower Cretaceous, which is distributed throughout the area. The evolutionary history shows that most of structures in the central troughs lack hydrocarbon potential, because they were formed since the Paleogene, which are later than the main accumulation period of the AG source rock. The fault terrace zones on both sides of the Kaikang trough have obtained petroleum discovery, but the distribution of oil layers is much complicated. Hydrocarbon accumulation is controlled by formation dips, fault activity intensity, and fault lateral docking characteristics. The weaker active fault block in late period and more effective trap are the key factors to hydrocarbon enrichment at the fault terrace zones. There are two typical reservoir-forming modes; one is the small fault distance reservoir-forming mode of the lower primary reservoir, and the other is the secondary reservoir-forming mode of the upper and middle combination.

Template-directed fabrication of zeolitic imidazolate framework-67-derived coating materials on nickel/titanium alloy fiber substrate for selective solid-phase microextraction

Novel solid-phase microextraction fibers were fabricated by electrochemical deposition of cobalt on the pretreated nickel/titanium alloy (NiTi) fiber substrate and subsequent in situ growth of zeolitic imidazolate framework-67 (ZIF-67) followed by annealing treatment. The Co@ZIF-67 coating was used as a precursor and template for controlled fabrication of the Co@ZIF-67-derived coatings including Co@ZIF-67-Co3O4 and carbonaceous composite coatings. . The extraction performance of the Co@ZIF-67-derived coatings was evaluated using typical aromatic compounds coupled to high-performance liquid chromatography with UV detection. The results clearly demonstrate that the extraction selectivity is subject to the surface elemental composition of the ZIF-67-derived coatings. In view of long-term stability and good extraction selectivity, the Co@ZIF-67-C coating was selected for the enrichment and determination of polycyclic aromatic hydrocarbons (PAHs). Under the optimized conditions, the calibration curves were linear in the range of 0.05–100 μg•L−1 with the correlation coefficients above 0.998. Limits of detection were 0.005–0.042 μg•L−1. Furthermore, the intra-day and inter-day repeatability of the proposed method with the single fiber varied from 2.3% to 5.8% and from 3.3% to 6.9%, respectively. The fiber-to-fiber reproducibility ranged from 4.1% to 8.5%. The proposed method was suitable for selective enrichment and determination of target PAHs from real water samples. Moreover, the fabricated fiber showed precisely controllable growth and 150 extraction and desorption cycles.

Improved methods for determining effective sandstone reservoirs and evaluating hydrocarbon enrichment in petroliferous basins

Geological uncertainty is the greatest risk in oil exploration. Most of the evaluation and risk assessment of exploration projects are characterized by the hydrocarbon enrichment evaluation of the target reservoir to avoid non-effective reservoirs. Based on experiments and detailed analysis of the hydrocarbon accumulation process, we propose a new criterion, namely reservoir hydrocarbon enrichment potential index, expressed as PI, for improved evaluation and assessment. According to the index PI, sandstone reservoirs are classified into four categories: Level IV, PI ≤ 0; Level III, 0 < PI ≤ 0.01; Level II, 0.01 < PI ≤ 0.1; Level I, 0.1 < PI ≤ 1. Level IV reservoirs are non-effective, whereas Level III, Level II, and Level I reservoirs are effective and their hydrocarbon enrichment potentials increase progressively. The recommended strategy is to prioritize the exploration of sandstone reservoirs in the order of Level I > Level II > Level III and avoid Level IV reservoirs. This strategy was applied to the Mesozoic sandstone in western Sichuan Depression, China, to demonstrate the method and workflow. Drilling success rate is positively correlated with the PI of the sandstone reservoir. The results of 153 wells drilled in western Sichuan Depression show the accuracy of the method to be 84.5%. Therefore, this method is useful for quick and effective scientific decisions on oil exploration projects, thus mitigating the risks in oil exploration projects.

Depositional and compositional controls on diagenesis of the mixed siliciclastic-volcaniclastic sandstones: A case study of the Lower Cretaceous in Erennaoer Sag, Erlian Basin, NE China

A succession of tight-oil mixed siliciclastic-volcaniclastic sandstones (MSVS) deposited in the Lower Cretaceous in the Erlian Basin has increasingly attracted attention for its significant discovery of oil and gas. The mixed compositions have a significant influence on diagenesis and reservoir properties. Understanding the relationship between lithofacies and diagenesis is of great value to providing an understanding of hydrocarbon enrichment potential in MSVS. The current investigation utilizes a multi-method approach including core analysis, petrography, SEM, microthermometry, and stable carbon- and oxygen-isotope geochemistry to better understand the mixed sandstones' lithofacies and controls on diagenesis. Three main sandstone lithofacies are composed of non-tuffaceous sandstone deposited in fan delta front (FFD-NTss), non-tuffaceous sandstone deposited in pro-fan delta (PFD-NTss), and tuffaceous sandstone deposited in pro-fan delta and lake (PFD-Tss). The results suggest that the early diagenetic stage of the MSVS includes the formation of chlorite and subhedral micritic-crystalline dolomite-1 cement (DI). The late stage includes the precipitation of quartz and calcite and subhedral to euhedral microcrystalline dolomite-2 cements (DII). FFD-NTss suffered from strong compaction due to abundant silt-sized and clay matrix whereas PFD-NTss was influenced by abundant calcite cementation due to weak compaction and more rigid debris. PFD-Tss contains abundant volcanic materials, alteration of which not only provided abundant ions but enhanced methanogenesis during the shallow burial, therefore, leading to formation of early diagenetic DI, analcime, and chlorite. Clay minerals are predominant in FFD-NTss whereas the late diagenetic calcite and dolomite cements are common in PFD-NTss that suffered from weak compaction. With the alteration of volcanic material and clay mineral transformations, the late diagenetic carbonate and clay minerals are widely distributed in the PFD-Tss.

Petroleum geological conditions and exploration potential of Lower Paleozoic carbonate rocks in Gucheng Area, Tarim Basin, China

Abstract Lower Paleozoic carbonate rocks are an important exploration area in craton area of the Tarim Basin, with the proven oil and gas reserves of more than 2.2×108 t, but no large-scale discovery has been made in the Gucheng area so far. The key issues restricting exploration are that the source rock, reservoir scale and law of oil and gas enrichment are unclear. By systematically examining the petroleum geological conditions of Lower Paleozoic carbonate rocks, the following findings are reached: (1) Source rocks of slope-basin facies developed in Cambrian-Lower Ordovician in the Gucheng area. (2) The dolomitized beach in the lower part of Ordovician Yingshan Formation has large-scale reservoirs, good reservoir-cap assemblage and developed gas source faults, and is an important field for increasing reserves and production in the near future; hydrocarbon enrichment is controlled by reservoir and gas source faults, and the central dolomitized beach zone is the main exploration area. (3) The Cambrian platform margin reef beach, large in scale, good in physical properties and close to source rocks, has the possibility to form monolithic gas field; the caprock and preservation conditions are the key factors for hydrocarbon enrichment; the northern part of the phases I and II platform margin reefs has better sealing conditions, and is the main direction of next exploration. (4) Limestone fault solution reservoirs in the upper part of Ordovician Yingshan Formation, controlled by faults and small in scale, but good in reservoir-cap combination, worth exploring. (5) The granular limestone beach of Ordovician Yijianfang Formation is well developed and gas-bearing, but short in exposure dissolution time, and the reservoirs are strongly heterogeneous, and are a potential exploration field.