Development Strategies for Achieving High Production with Fewer Wells in Conventional Offshore Heavy Oil Fields in Bohai Bay,China

Development strategy for heavy-oil reservoirs is one of the important research interests in China National Offshore Oil Corp. （CNOOC） that plans a highly effective development for heavy oil fields in multilayered fluvial reservoirs because of their significant influence on marine oil and even on China＇s petroleum production. The characteristics analysis of multilayered fluvial reservoirs in the heavy oil fields in Bohai Bay indicates that large amounts ofoil were trapped in the channel, point bar and channel bar sands. The reserves distribution of 8 oilfields illustrates that the reserves trapped in the main sands, which is 20%-40% of all of the sand bodies, account for 70%-90% of total reserves of the heavy oil fields. The cumulative production from high productivity wells （50% of the total wells） was 75%-90% of the production of the overall oilfield, while only 3%-10% of the total production was from the low productivity wells （30% of the total wells）. And the high productivity wells were drilled in the sands with high reserves abundance. Based on the above information the development strategy was proposed, which includes reserves production planning, selection of well configuration, productivity design, and development modification at different stages.

Sandbody architecture of the bar finger within shoal water delta front:Insights from the Lower Member of Minghuazhen Formation,Neogene,Bohai BZ25 Oilfield,Bohai Bay Basin,East China

Core, well logging and seismic data were used to investigate sandbody architectural characteristics within Lower Member of Minghuazhen Formation in Neogene, Bohai BZ25 Oilfield, and to analyze the sedimentary microfacies, distribution and internal architecture characteristics of the bar finger within shoal water delta front. The branched sand body within shoal water delta front is the bar finger, consisting of the mouth bar, distributary channel over bar, and levee. The distributary channel cuts through the mouth bar, and the thin levee covers the mouth bar which is located at both sides of distributary channel. The bar finger is commonly sinuous and its sinuosity increases basinward. The distributary channel changes from deeply incising the mouth bar to shallowly incising top of the mouth bar.The aspect ratio ranges from 25 to 50 and there is a double logarithmic linear positive relationship between the width and thickness for the bar finger, which is controlled by base-level changing in study area. For the bar finger, injection and production in the same distributary channel should be avoided during water flooding development. In addition, middle–upper distributary channel and undrilled mouth bar are focus of tapping remaining oil.

Characteristics of the sea ice reflectance spectrum polluted by oil spills based on field experiments in the Bohai Sea

Oil spilled on the sea ice surface in the Bohai Sea of China is studied through the field measurements of the reflectance of a simulated sea ice-oil film mixed pixel. The reflection characteristics of sea ice and oil film are also analyzed. It is found that the mixed pixel of sea ice and oil film is a linear mixed pixel. The means of extracting sea ice pixels containing oil film is presented using a double-band ratio oil-film sea-ice index（DROSI） and a normalized difference oil-film sea-ice index（NDOSI） through the analysis of the reflectance curves of the sea iceoil film pixel for different ratios of oil film. The area proportion of the oil film in the sea ice-oil film pixel can be accurately estimated by the average reflectance of the band of 1 610–1 630 nm, and the volume of the spilled oil can be further estimated. The method of the sea ice-oil film pixel extraction and the models to estimate the proportion of oil film area in the sea ice-oil film pixel can be applied to the oil spill monitoring of the ice-covered area in the Bohai Sea using multispectral or hyperspectral remote sensing images in the shortwave infrared band（1 500–1 780 nm）.

Occurrence mechanism of lacustrine shale oil in the Paleogene Shahejie Formation of Jiyang Depression, Bohai Bay Basin, China

To determine the occurrence mechanism and mobility of shale oil in the Shahejie Formation in the Jiyang Depression, organic geochemistry analysis, thin-section petrological observation, low-temperature nitrogen adsorption, high-pressure mercury intrusion porosimetry, field emission scanning electron microscopy experiments were conducted on shale samples to reveal its storage mechanism, including pore size, ratio of adsorbed oil to free oil, mobility and its influencing factors, and mode of storage. Residual shale oil is mainly present in pores less than 100 nm in diameter under the atmospheric temperature and pressure. The lower limit of pore size for free oil is 5 nm, and the lower limit of pore size for movable oil occurrence is about 30 nm. The light components, low TOC and high porosity are the main factors contributing to the high proportion of movable oil. Each type of pore can contain residual shale oil, but not all pores have shale oil. Pore connectivity and surface wettability are the determinants of shale oil enrichment degree and enrichment state.

Biodegraded Oil and Its High Molecular Weight (C_(35+)) n-alkanes in the Qianmiqiao Region in the Bohai Bay Basin, Northern China

With a production of 208.2 m3/d, heavy oil was produced by drill stem test (DST) from three shallow reservoirs in Sand Group Nos. Ⅰ and Ⅲ of the Neogene Guantao Formation (NgⅠ and NgⅢ) and the Eogene Dongying Formation (Ed) in an exploratory well Ban-14-1 within the Qianmiqiao region, Bohai Bay Basin, northern China. Based on the GC and GC-MS data of the NgⅠ and NgⅢ heavy oil samples, all n-alkanes and most isoprenoid hydrocarbons are lost and the GC baseline appears as an evident 'hump', implying a large quantity of unresolved complex mixture (UCM), which typically revealed a result of heavy biodegradation. However, there still is a complete series of C14-C73 n-alkanes in the high-temperature gas chromatograms (HTGC) of the heavy oil, among which, the abundance of C30- n-alkanes are drastically reduced. The C35-C55 high molecular weight (HMW) n-alkanes are at high abundance and show a normal distribution pattern with major peak at C43 and an obvious odd-carbon-number predominance with CPI37-55 and OEP45-49 values of 1.17 and 1.16-1.20, respectively. According to GC-MS analysis, the heavy oil is characterized by dual source inputs of aquatic microbes and terrestrial higher plants. Various steranes and tricyclic terpanes indicate an algal origin, and hopane-type triterpanes, C24 tetracyclic terpane and drimane series show the bacterial contribution. With the odd-carbon-number preference, HMW n-alkanes provide significant information not only on higher plant source input and immaturity, but also on the strong resistibility to biodegradation.

Characteristics and Controlling Factors of Shale Oil Reservoir Spaces in the Bohai Bay Basin

The Cenozoic continental strata of the Bohai Bay Basin are rich in shale oil resources, and they contain various types of reservoir spaces that are controlled by complex factors. Using field emission scanning electron microscopy(FESEM), automatic mineral identification and characterization system(AMICS), CO2 and N2 gas adsorption, and focused ion beam scanning electron microscopy(FIB-SEM), the types of shale reservoir spaces in the Bohai Bay Basin are summarized, the spatial distribution and connectivity of the various types of pores are described in detail, the microscopic pore structures are characterized, and the key geological mechanisms affecting the formation and evolution of the reservoir spaces are determined. Three conclusions can be drawn in the present study. First, the shale reservoir spaces in the Bohai Bay Basin can be divided into three broad categories, including mineral matrix pores, organic matter pores, and micro fractures. Those spaces can be subdivided into seven categories and fourteen sub-categories based on the distribution and formation mechanisms of the pores. Second, the complex pore-throat structures of the shale reservoir can be divided into two types based on the shape of the adsorption hysteresis loop. The pore structures mainly include wedge-shaped, flat slit-shaped, and ink bottle-shaped pores. The mesopores and micropores are the main contributors to pore volume and specific surface area, respectively. The macropores provide a portion of the pore volume, but they do not significantly contribute to the specific surface area. Third, the factors controlling the development of microscopic pores in the shale are complex. The sedimentary environment determines the composition and structure of the shale and provides the material basis for pore development. Diagenesis controls the types and characteristics of the pores. In addition, the thermal evolution of the organic matter is closely related to inorganic diagenesis and drives the formation and evolution of the pores.

An exploration breakthrough in Paleozoic petroleum system of Huanghua Depression in Dagang Oilfield and its significance, North China

In recent years, several wells in the Qibei and Wumaying buried hills of Dagang Oilfield tapped oil in the Carboniferous–Permian and Ordovician strata. This major breakthrough reveals that the deep Paleozoic in the Bohai Bay is a new petroleum system. Through re-evaluating the Paleozoic source rock, reservoir-cap combinations and traps, it is found the oil and gas mainly come from Carboniferous–Permian source rock. The study shows that the Paleozoic strata are well preserved in the central-south Huanghua Depression and developed two kinds of reservoirs, Upper Paleozoic clastic rock and Lower Paleozoic carbonate rock, which form favorable source-reservoir assemblages with Carboniferous–Permian coal measure source rock. The Carboniferous–Permian coal-bearing source rock is rich in organic matters, which are mainly composed of type Ⅱ2 and Ⅲ kerogens, and minor Ⅱ1 kerogen in partial areas. Multi-stage tectonic movements resulted in two stages of hydrocarbon generation of the source rocks. The period from the deposition of Kongdian Formation to now is the second stage of hydrocarbon generation. The matching between large-scale oil and gas charging, favorable reservoir-cap combinations and stable structure determines the enrichment of oil and gas. According to the new comprehensive evaluation of Paleozoic petroleum system, the primary oil and gas resources of the Paleozoic in the Bohai Bay Basin are over 1×1012m3. The exploration breakthrough in Paleozoic petroleum system, especially Carboniferous–Permian petroleum system in Huanghua Depression is inspirational for oil and gas exploration in similar provinces of Bohai Bay Basin.

Geological characteristics of shale rock system and shale oil exploration breakthrough in a lacustrine basin:A case study from the Paleogene 1st sub-member of Kong 2 Member in Cangdong sag,Bohai Bay Basin,China

A deep understanding of the basic geologic characteristics of the fine-grained shale layers in the Paleogene 1 st sub-member of Kong 2 Member(Ek_2~1) in Cangdong sag, Bohai Bay Basin, is achieved through observation of 140 m continuous cores and systematic analysis of over 1 000 core samples from two wells. Basic geological conditions for shale oil accumulation are proposed based on the unconventional geological theory of oil and gas. The shale rock system mainly developed interbedded formation of felsic shale, calcareous and dolomitic shale and carbonates; high quality hydrocarbon source rock formed in the stable and closed environment is the material base for shale oil enrichment; intergranular pores in analcite, intercrystalline pores in dolomite and interlayer micro-fractures make tight carbonate, calcareous and dolomitic shale and felsic shale effective reservoirs, with brittle mineral content of more than 70%; high abundance laminated shale rock in the lower section of Ek_2~1 is rich in shale oil, with a total thickness of 70 m, burial depth between 2 800 to 4 200 m, an average oil saturation of 50%, a sweet spot area of 260 km^2 and predicted resources of over 5×10~8 t. Therefore, this area is a key replacement domain for oil exploration in the Kongdian Formation of the Cangdong sag. At present, the KN9 vertical well has a daily oil production of 29.6 t after fracturing with a 2 mm choke. A breakthrough of continental shale oil exploration in a lacustrine basin is expected to be achieved by volume fracturing in horizontal wells.

Numerical Simulation of Bohai Oil Spill in the Winter Sea Ice Period

The Bohai Sea is a seasonal icy sea area that has the lowest latitude of any sea experiencing icing in the northern hemisphere, and simulation studies on oil spills during its sea ice period are the key to analyzing winter oil spill accidents. This study applied the three-dimensional free surface to establish a high-resolution hydrodynamic model and simulate tidal distributions in the Bohai Sea. Then, the oil spill model of the open sea area and thermodynamic model were combined to establish a numerical model for the Bohai oil spill during the winter sea ice period. The hydrodynamic model and sea ice growth and melting model were verified, and the parameters were adjusted based on the measured values, which indicate that the numerical model established in this paper is of high accuracy,stability and ubiquity. Finally, after checking the calculations repeatedly, the diffusion coefficient for the Bohai Sea was determined to be 1.0×10^(–7 )m^2/s. It is better that the comprehensive weathering attenuation coefficient is lower than that of a non-winter oil spill, with 1.3×10^(–7 )m^2/s being the most appropriate coefficient. This study can provide the reliable technical support for the operational safety and reduction in losses caused by winter oil spill accidents for the petroleum industry.

Oil Spill Risk Assessment of Offshore Pipeline in the Bohai Sea Under the Perspective of Ecological Protection

In recent decades,the exploration and development of marine oil and gas resources have increased significantly to meet the increasing energy demand of mankind.The Bohai Sea is a semi-closed continental sea that has a weak water exchange capacity and high ecological fragility.However,at present,more than 200 oil platforms have been built in the Bohai Sea,with more than 270 offshore oil pipelines having a length exceeding 1600 km.The oil spill pollution of offshore platforms has a great impact on the marine environment and ecosystems.Therefore,a comprehensive assessment of its risks is of great practical significance.This paper systematically constructs a comprehensive oil spill risk assessment model that combines the oil spill risk probability model and the ocean hydrodynamic model.This paper uses the Bohai Sea offshore pipeline as an example to assess its oil spill risk.The high-risk-value areas of the Bohai Sea offshore pipeline are mainly distributed at the bottom of Liaodong Bay,the bottom of Bohai Bay,near the Caofeidian area,and the northern part of the Yellow River Estuary.

The Research and Applications of Remaining Oil Potential Tapping in High Watered Stage for Heavy Oil Reservoir in Bohai

S oil field is a typical of water injection development of heavy oil reservoir in Bohai, and the formation of crude oil viscosity is 42 - 284 mPa?s. Due to the formation of crude oil viscosity, the oil field development gradually faces a series of problems as rapid rise of water cut, rapid decline of output, high water cut of oil wells and others. In order to improve the effect of oilfield development, it is necessary to increase the output of the oilfield by adjusting wells for the potential in the oilfield. However, due to the high cost of drilling, operation and testing of offshore oilfields, offshore oilfields require more elaborate description of residual oil and adjustment wells. With the continuous downturn in international oil prices and the lack of new testing data in old oilfields, it is urgent to re-use the existing data in oilfields through innovative methods to achieve a detailed description of the remaining oil in the oilfields and improve the precision research of indexing wells and ensure the reliable implementation of adjustment wells. Based on the existing dynamic data of S oilfield, this paper proposes a new method to quantitatively evaluate water flooding coefficient by using tracer theory to establish tracer data, and quantitatively evaluates the vicinity of the fault by means of image reflection and potential superposition and find the residual oil in the imperfect area of the well network, combined with the numerical simulation method to realize the fine description of remaining oil and improve the research precision of the adjustment well. Through the research in this paper, S oilfield has proposed to location of six adjustment wells which has implemented two. The production confirmed that the method of this paper has some reliability, while the method of heavy oil in the high water cut stage of residual oil fine description. The research of enhanced oil recovery in the stage has certain guiding significance for heavy oil reservoirs.

Organic geochemical characteristics of Eocene crude oils from Zhanhua Depression,Bohai Bay Basin,China

Geochemical studies of crude oil and source rock play an important role in future exploration in Zhanhua Depression.In this study,thirty-one oil samples collected from Shahejie Formation in Zhanhua Depression,Bohai Bay Basin,NE China have been geochemically analyzed and their organic geochemical characteristics have been applied to differentiate groups of oils.These oil samples can be classified into two families based on multiple biomarker proxies and stable carbon isotopic values.FamilyⅠis characterized by a low ratio of pristane over phytane(Pr/Ph<0.7),a relatively high ratio of phytane over n-C18(Ph/n-C18),varying ratios of gammacerane over C30 hopane(Ga/C30H)and C22/C21 tricyclic terpane,and a low ratio of C19/C23 tricyclic terpane.FamilyⅡis marked by a relatively high Pr/Ph ratio(0.7-1.6),relative low ratios of Ph/n-C18 and C22/C21 tricyclic terpane,and avarying ratio of C19/C23 tricyclic terpane.Both familiesⅠandⅡwithin these crude oils can be subdivided into two families based on different values of stable carbon isotopic composition of individual n-alkanes.Moreover,the potential source rocks of oil samples in FamilyⅠand FamilyⅡwere likely derived from the upper Es4 member and Es3 member,respectively,based on the correlation of organic geochemical characteristics of the oils and source rocks.The results of oil-source rock correlation provide insight into the process from oil generation to migration and to final accumulation,providing a better understanding of factors controlling oil-gas distribution for prediction of sweet spots.

Key exploration & development technologies and engineering practice of continental shale oil: A case study of Member 2 of Paleogene Kongdian Formation in Cangdong Sag, Bohai Bay Basin, East China

Based on detailed core description and systematic joint test data,enrichment laws of continental shale oil have been examined deeply.Key technologies such as the identification and quantitative evaluation method for sweet spot,precise design and tracking of horizontal well trajectory,and the low-cost horizontal well volume fracturing technology of the whole process"slick water+quartz sand"for continental shale oil have been formed.The research results show that the enrichment of pure continental shale oil of the Paleogene Kong 2 Member in Cangdong Sag is controlled by predominant fabric facies and cross-over effect of retained hydrocarbons jointly;and there are four modes of shale oil enrichment,i.e.laminar felsic,laminar mixed,thin-layer limy dolomitic,and thick-layer limy dolomitic shales.The identification and evaluation method for shale oil sweet spots can predict sweet spots accurately.The precise trajectory design for sweet spot layer and tracking-trajectory optimization while drilling by considering geological and engineering factors have been proved effective by field application,with drilling rate of sweet spots reaching 100%and drilling rate of type I sweet spots reaching over 75%.The whole process"slick water+quartz sand"low cost volume fracturing has been proved effective in creating multi-stage fracture network in the horizontal section,and improved productivity greatly.It can lower the comprehensive engineering cost by 26.4%.

Sweet spot evaluation and exploration practice of lacustrine shale oil of the second member of Kongdian Formation in Cangdong sag, Bohai Bay Basin

Based on core,thin section,X-ray diffraction,rock pyrolysis,CT scanning,nuclear magnetic resonance and oil testing data,the macro and micro components,sedimentary structure characteristics,of Paleogene Kong 2 Member in Cangdong sag of Huanghua depression and evaluation standard and method of shale oil reservoir were studied to sort out the best shale sections for shale oil horizontal wells.According to the dominant rock type,rhythmic structure and logging curve characteristics,four types of shale lithofacies were identified,namely,thin-layered dolomitic shale,lamellar mixed shale,lamellar felsic shale,and bedded dolomitic shale,and the Kong 21 sub-member was divided into four quasi-sequences,PS1 to PS4.The PS1 shale has a porosity higher than 6%,clay content of less than 20%,and S1 of less than 4 mg/g;the PS2 shale has well-developed laminar structure,larger pore and throat size,better connectivity of pores and throats,high contents of TOC and movable hydrocarbon,S1 of over 4 mg/g,clay content of less than 20%,and porosity of more than 4%;PS3 shale has S1 value higher than 6 mg/g and clay content of 20%-30%,and porosity of less than 4%;and PS4 shale has lower TOC content and low oil content.Shale oil reservoir classification criterion based on five parameters,free hydrocarbon content S1,shale rhythmic structure,clay content,TOC and porosity,was established.The evaluation method of shale oil sweet spot by using the weighted five parameters,and the evaluation index EI were proposed.Through comprehensive analysis,it is concluded that PS2 is best in quality and thus the dual geological and engineering sweet spot of shale oil,PS3 and PS1 come next,the former is more geologic sweet spot,the latter more engineering sweet spot,and PS4 is the poorest.Several vertical and horizontal wells drilled in the PS2 and PS3 sweet spots obtained high oil production.Among them,Well 1701 H has produced stably for 623 days,with cumulative production of over 10000 tons,showing bright exploration prospects of Kong 2 Member shale oil.

i4OilS pill, an Operational Marine Oil Spill Forecasting Model for Bohai Sea

Oil spill models can effectively simulate the trajectories and fate of oil slicks, which is an essential element in contingency planning and effective response strategies prepared for oil spill accidents. However, when applied to offshore areas such as the Bohai Sea, the trajectories and fate of oil slicks would be affected by time-varying factors in a regional scale, which are assumed to be constant in most of the present models. In fact, these factors in offshore regions show much more variation over time than in the deep sea, due to offshore bathymetric and climatic characteristics. In this paper, the challenge of parameterizing these offshore factors is tackled. The remote sensing data of the region are used to analyze the modification of wind-induced drift factors, and a well-suited solution is established in parameter correction mechanism for oil spill models. The novelty of the algorithm is the self-adaptive modification mechanism of the drift factors derived from the remote sensing data for the targeted sea region, in respect to empirical constants in the present models. Considering this situation, a new regional oil spill model(i4Oil Spill) for the Bohai Sea is developed, which can simulate oil transformation and fate processes by Eulerian-Lagrangian methodology. The forecasting accuracy of the proposed model is proven by the validation results in the comparison between model simulation and subsequent satellite observations on the Penglai 19-3 oil spill accident. The performance of the model parameter correction mechanism is evaluated by comparing with the real spilled oil position extracted from ASAR images.

Formation conditions and exploration direction of large natural gas reservoirs in the oil-prone Bohai Bay Basin, East China

The Bohai Bay Basin is a typical oil-prone basin, in which natural gas geological reserves have a small proportion. In this basin, the gas source rock is largely medium-deep lake mudstone with oil-prone type Ⅱ2-Ⅱ1 kerogens, and natural gas preservation conditions are poor due to active late tectonic movements. The formation conditions of large natural gas fields in the Bohai Bay Basin have been elusive. Based on the exploration results of Bohai Bay Basin and comparison with large gas fields in China and abroad, the formation conditions of conventional large-scale natural gas reservoirs in the Bohai Bay Basin were examined from accumulation dynamics, structure and sedimentation. The results show that the formation conditions of conventional large natural gas reservoirs in Bohai Bay Basin mainly include one core element and two key elements. The core factor is the strong sealing of Paleogene "quilt-like" overpressure mudstone. The two key factors include the rapid maturation and high-intensity gas generation of source rock in the late stage and large scale reservoir. On this basis, large-scale nature gas accumulation models in the Bohai Bay Basin have been worked out, including regional overpressure mudstone enriching model, local overpressure mudstone depleting model, sand-rich sedimentary subsag depleting model and late strongly-developed fault depleting model. It is found that Bozhong sag, northern Liaozhong sag and Banqiao sag have favorable conditions for the formation of large-scale natural gas reservoirs, and are worth exploring. The study results have important guidance for exploration of large scale natural gas reservoirs in the Bohai Bay Basin.

Carbon isotopic compositions of mono-, di-, tri-aromatics provide insights into the source of sulfur-rich crude oils in the Huanghekou Depression, Bohai Bay Basin

The stable carbon isotope compositions (δ13C) of individual aromatic hydrocarbons have been analyzed in sulfur-rich and sulfur-lean crude oils from the Huanghekou Depression, Bohai Bay Basin. The δ13C values of individual aromatic hydrocarbons, including alkylbenzenes, alkylnaphthalenes, alkylphenanthrenes, alkylfluorenes and alkyldibenzothiophenes, are reported. The main aims are to find out the origin of these oils and their relationship to paleoclimate. The distribution of aromatic hydrocarbons and maturity parameters show the oils all stay in the low-mature to mature stage. Meanwhile, aromatic hydrocarbons are mainly derived from the diagenetic/catagenetic origin. The δ13C values for 1,2,4-trimethylbenzene (−30.7‰ to −28.8‰) and 1,2,3,4-tetramethylbenzene (−32.4‰ to −26.3‰) indicate the algae-derived organic matter for alkylbenzenes. Some isomers, such as 1,7-+1,3-+1,6-dimethylnaphthalene, 1,2,5-trimethylnaphthalene, 1,2,5,6-+1,2,3,5-tetramethylnaphthalene, 1,10-+1,3-+3,10-+3,9-dimethylphenanthrenes, 1,6-+2,9-+2,5-dimethylphenanthrenes and 4,9-+4,10-+1,9- dimethylphenanthrenes show isotopic depletion (−34.9‰ to −25.2‰), indicating the major contribution of algae for these compounds. Meanwhile, isotopically depleted (−33.6‰ to −26.7‰) alkyldibenzothiophenes represent the algae input. δ13C values for mainly algae-derived naphthalene to trimethylnaphthalenes of sulfur-rich oils are more enriched than those of sulfur-lean oil, with the most significant difference of 4.4‰, indicating that the aridity of the environment and stratified water column result in the enrichment in 13C.

Structural characteristics of continental carbonate-rich shale and shale oil movability: A case study of the Paleogene Shahejie Formation shale in Jiyang Depression, Bohai Bay Basin, China

Based on rock mineral and geochemical analysis, microscopic observation, physical property measurement, and thin laminae separation test, etc., the characteristics of typical laminae of the Paleogene Shahejie Formation carbonate-rich shale in the Jiyang Depression were analyzed, and the organic matter abundance, reservoir properties, and oil-bearing properties of different laminae were compared. Typical shale storage-seepage structures were classified, and the mobility of oil in different types of shale storage-seepage structure was compared. The results show that the repeated superposition of mud laminae and calcite laminae are the main layer structure of carbonate-rich shales. The calcite laminae are divided into micritic calcite laminae, sparry calcite laminae and fibrous calcite vein. The mud-rich laminae are the main contributor to the organic matter abundance and porosity of shale, with the best hydrocarbon generation potential, reservoir capacity, and oil-bearing property. The micritic calcite laminae also have relatively good hydrocarbon generation potential, reservoir capacity and oil-bearing property. The sparry calcite laminae and fibrous calcite vein have good permeability and conductivity. Four types of shale storage-seepage structure are developed in the carbonate-rich shale, and the mobility of oil in each type of storage-seepage structure is in descending order: sparry calcite laminae enriched shale storage-seepage structure, mixed calcite laminae enriched shale storage-seepage structure, fibrous calcite vein enriched shale storage-seepage structure, and micritic calcite laminae enriched shale storage-seepage structure. The exploration targets of carbonate-rich shale in the Jiyang Depression Shahejie Formation are different in terms of storage-seepage structure at different thermal evolution stages.

Assessing impact of oil spills in fairways in Chinese Bohai Sea with the impact matrix method

The density of traffic in Bohai Sea of China is growing,so the evaluation of the impact of potential oil spills becomes necessary.However,the impact of potential oil spills at a large temporal-spatial scale has seldom been studied.In this paper,the effects of potential oil spills in seven main fairways in Chinese Bohai Sea and the risks of five environmental sensitive areas(ESAs)being polluted are studied.A three-dimensional hydrodynamic model,coupled with Lagrangian particle tracking model,was constructed to simulate the transportation of oil spills.Hypothetical oil particles with an idealized,passive tracer were released along fairways and their transportation over20-day and180-day periods were simulated,respectively.An environmental impact matrix was built to reveal the relationship between oil spills in fairways and the pollution of ESAs.Results showed that in short term,Z4and Z5had high risk of being polluted by oil spills.Oil particles released along Fairways1,2and7had strong pollution effects.In long term,Z1,Z3,Z4and Z5had medium risk of being polluted.Oil particles released along Fairway3had strong pollution effects.This study might provide useful data to support marine environment protection.