East China Sea Basin Research Articles

Sources of Natural Gases in the Xihu Sag, East China Sea Basin: Insights from Stable Carbon Isotopes and Confined System Pyrolysis

The Xihu Sag is the most gas-rich area in the East China Sea Basin. However, the origin of the natural gases is still controversial. Twenty-seven natural gas samples collected from the Xihu Sag wer...

3D-Basin Modelling of the Lishui Sag: Research of Hydrocarbon Potential, Petroleum Generation and Migration

The Lishui Sag is located in the southeastern part of the Taibei Depression, in the East China Sea basin, where the sag is the major hydrocarbon accumulation zone. A three dimensional modelling approach was used to estimate the mass of petroleum generation and accumulated during the evolution of the basin. Calibration of the model, based on measured maturity (vitrinite reflectance) and borehole temperatures, took into consideration two main periods of erosion events: a late Cretaceous to early Paleocene event, and an Oligocene erosion event. The maturation histories of the main source rock formations were reconstructed and show that the peak maturities have been reached in the west central part of the basin. Our study included source rock analysis, measurement of fluid inclusion homogenization temperatures, and basin history modelling to define the source rock properties, the thermal evolution and hydrocarbon generation history, and possible hydrocarbon accumulation processes in the Lishui Sag. The study found that the main hydrocarbon source for the Lishui Sag are argillaceous source rocks in the Yueguifeng Formation. The hydrocarbon generation period lasted from 58 Ma to 32 Ma. The first period of hydrocarbon accumulation lasted from 51.8 Ma to 32 Ma, and the second period lasted from 23 Ma to the present. The accumulation zones mainly located in the structural high and lithologic-fault screened reservoir filling with the hydrocarbon migrated from the deep sag in the south west direction.

Tectonic Evolution of Late Mesozoic–Cenozoic Basins in Eastern China and Implications for Pacific Plate Subduction

Abstract —During the late Mesozoic and Cenozoic, the North China Craton witnessed a series of tectonic transition and deformation events, caused mainly by the subducting Pacific Plate and forming many petroliferous basins in eastern China and adjacent areas. Based on analysis related to the reconstruction of balanced sections, the comparison of subsidence rates, and the migration of depocenters in these basins, the tectonic evolution of these basins and their relationships with each other are clearly revealed. The evolution of the Bohai Bay Basin shows a migration from southwest to northeast. The North Yellow Sea Basin’s evolution developed northward, while the South Yellow Sea Basin evolution migrated southwards. The evolution of the East China Sea Basin was activated from northwest to southeast. In combination with the subduction of the Pacific Plate, the conclusions of this study can be summarized in three aspects: (1) The structural pattern of the basin group is characterized by east–west trending belts and north–south trending blocks, (2) tectonic activities in the late Mesozoic–Cenozoic basins evolved from west to east in response to the westward subduction of the Pacific Plate, and (3) due to the collision of the Eurasian Plate and Indian Plate and the transitional pattern of the Tan-Lu Fault Zone from sinistral to dextral, the tectonic evolution of the basin group was centered in the Yellow Sea Basin with the Bohai Bay Basin, evolution migrating northward and the ECSB migrating southward.

Reservoir controlling factors of the Paleogene Oligocene Huagang Formation in the north central part of the Xihu Depression, East China Sea Basin, China

Huagang Formation is a typical offshore, deep, low-permeability, tight sandstone reservoir with a low level of exploration and development and unclear control factors in the North Central area of the Xihu Depression in the East China Sea Basin. In this paper, we begin with the analysis of basic data, such as cores, casting thin sections, cathode luminescence, scanning electron microscopy, physical property statistics, grain size analysis, mercury penetration and magnetic resonance imaging, combined with field logging data from conventional logging, imaging logging and three-dimensional seismic imagery. The reservoir's physical properties were comprehensively discussed in terms of provenance, deposition, diagenesis and fractures. The results showed that the reservoir physical properties of the Huagang Formation were mainly affected by compaction, and the porosity and permeability decreased with the depth of burial. When the depth exceeds 4000 m, the porosity is basically <10% and the permeability is nearly <1 mD. The compaction above 4000 m was mainly controlled by provenance and depositional microfacies. The reservoir physical properties in the northern provenance is better than that of the east provenance. A high-energy braided channel is the best physical depositional microfacies. The reservoir formed by event sedimentation, such as from storms and floods, due to poor sorting, often containing mud and so on, with poor physical properties. Carbonate cementation only had a great influence on the local reservoir. Illite, illite/smectite and pore-filling chlorite were important factors affecting physical property deterioration. Pore-lining chlorite can promote the retention of primary pores. Below 4000 m, favorable reservoirs were mainly controlled by dissolution, resulting in dissolution pores being the main reservoir space. Microfractures played an important role in the properties of low-permeability and tight reservoirs. Microfractures themselves were easily dissolved into dissolution pores while being an important seepage channel for low-permeability and tight reservoirs. The denser the reservoir is, the more important the microfracture seepage is.

Charge history of CO2 in Lishui sag, East China Sea basin: Evidence from quantitative Raman analysis of CO2-bearing fluid inclusions

Abstract The accumulation of carbon dioxide in natural gas reservoirs is common, and CO2 gas fields have been widely discovered in the world. In the last decades, three CO2 pools were discovered in Lishui sag, East China Sea Basin. Geochemical proxies indicate that CO2 in these gas reservoirs is dominated by mantle-source volcano degassing. Although three volcanic events occurred in the formation of these reservoirs, the CO2 charging period is not clear. In this study, pure CO2, CO2-rich and H2O-rich fluid inclusions were found in healed micro-fractures and overgrowth zones of quartz in the reservoir of Lishui sag. The composition and density of two H2O-rich inclusions, two CO2-rich inclusions and twenty-three pure CO2 inclusions were determined by Raman quantitative analysis. The burial depth of CO2 fluid inclusion assemblages (FIA) can be determined by the trapping pressure constrained from Raman quantitative analysis and thermodynamic models. The combination of C-He isotope analyses, PT entrapment conditions of CO2-bearing inclusions, feature of fault activity and simulation of burial history permits to assign periods of CO2 fluid activity. The low-density (∼0.15 g cm−3) CO2 gas inclusions recorded an early-period of CO2 activity eruption to be related with the Late-Paleocene volcanic event. The mid-density (∼0.45 g cm−3) and high-density (∼0.75 g cm−3) CO2 inclusions were assigned to the Miocene volcanic event and to a later CO2 charging event during Pliocene.

A new method to establish NMR T2 spectrum based on bimodal Gaussian density function: A case study of tight sandstone in East China Sea Basin

The identification and evaluation of tight sandstone reservoirs has been very difficult due to their low porosity, low permeability, complex pore structure and strong heterogeneity. In order to evaluate the quality of tight sandstone reservoir, priority should be given to the quantitative evaluation of pore size. Nuclear magnetic resonance (NMR) log is frequently employed in pore size evaluation; however, due to its high technical costs and other limitations, it can only be conducted in very few wells and the wide application can never be found. In this study, 12 core samples from the tight sandstone in East China Sea Basin have been collected to conduct centrifugal NMR experiments. Based on the analysis of data obtained from experiments, it is discovered that the bimodal Gaussian density function is well fitted to the NMR T2 spectrum and can be applied to the fitting of NMR T2 spectrum. Furthermore, in the analysis of physical property parameters of reservoir and each individual parameter of bimodal Gaussian density function, it is indicated that the porosity and permeability are best correlated with them. Therefore, the empirical formula between porosity, permeability and the parameters of bimodal Gaussian density function were established to construct pseudo NMR T2 spectrum by using bimodal Gaussian density function and it has been verified by the comparison between the result and experimental data. In order to achieve the more accurate and wide application of this method, the NMR T2 spectrum versus proportion frequency curve was transformed into the pore radius R versus porosity component Pφ curve before the fitting. When used in exploration field, the method can construct continuous pore size distribution curve which can be used for the quantitative evaluation of tight sandstone reservoir's quality. Compared with the method of NMR logging, this technique can be applied to the evaluation of pore structure of tight sandstone reservoirs more widely.

Trace and rare earth element (REE) characteristics of mudstones from Eocene Pinghu Formation and Oligocene Huagang Formation in Xihu Sag, East China Sea Basin: Implications for provenance, depositional conditions and paleoclimate

Abstract The interpretation of depositional conditions, provenance and paleoclimate provide important information to understand hydrocarbon source rock formation and distribution. The concentrations of trace elements and rare earth elements (REEs) of fifty mudstone samples from Eocene Pinghu Formation and Oligocene Huagang Formation in Xihu Sag, East China Sea Basin were determined by inductively coupled plasma-mass spectrometry (ICP-MS) to test the depositional conditions, provenance and paleoclimate. Evidences from the visual comparisons of the simple bivariate plots diagrams and statistical comparisons of the Mann-Whitney Rank Sum Test suggest that there may be a common source for the Pinghu Formation and Huagang Formation mudstones. Sedimentary provenance from bivariate plots diagrams of Hf versus La/Th and La/Sc versus Co/Th shows that Pinghu Formation mudstones are mainly composed of mixed felsic/basic source and acidic source whereas Huagang Formation is mainly acidic source. Additionally, the ∑REE vs La/Yb discrimination diagram shows that the property of the provenance for the Pinghu Formation mudstones consists sedimentary rock, alkaline basalt and a small amount of continent tholeiitic basalts whereas that of the Huagang Formation is mainly alkaline basalt and sedimentary rock. Discriminant diagrams, consisting of La-Th-Sc and Th-Co-Zr/10, suggest that the mudstones of two formations were deposited in continental island arc and active continental margin tectonic setting. Redox proxies (V/Ni, V/(V + Ni) and δCe) indicate that most of the mudstones of two formations were deposited in a relatively dysoxic/anoxic condition. The cool and humid climate (represented by Sr/Cu and Rb/Sr ratios) were prevailing in Xihu Sag during the Eocene and Oligocene period, and the Oligocene was cooler than Eocene. Moreover, five long term base level cycles (SIII1∼SIII5) and four sequence boundaries (Sb2∼Sb5) were recognized in the Pinghu Formation and Huagang Formation based on the previous research. We find that the abnormal surfaces of geochemical parameters, such as V/Ni, Sr/Ba, U/Ti, V/Ti, Ti and ΣREE, to some extent, agree with sequence boundaries (Sb2, Sb3, Sb4 and Sb5) in mudstones. Additionally, the increment of Ti and ΣREE concentrations and the decrease of Sr/Ba, V/Ni, U/Ti and V/Ti ratios above the Sb4 indicates that terrigenous clast grew significantly and the sea level dropped after late Eocene, which is related with the late Eocene tectonic movement.

The characteristics of low permeability reservoirs, gas origin, generation and charge in the central and western Xihu depression, East China Sea Basin

Apart from conventional gas in the middle-shallow formation in the Xihu depression in the East China Sea Basin, low permeability gas sandstone layers in the middle-deep formation have recently been discovered. On the basis of integrated analysis of reservoir petrology and diagenesis, geochemistry of gas and source rocks, basin numerical modeling, gold-tube pyrolysis experiment of rocks and fluid inclusion, a comprehensive investigation of the characteristics of low-permeability reservoirs, gas origin, generation and charge in the sub-structural belts (West Slope Belt and West Sub Sag) has been performed. Strong mechanical compaction, filar authigenic illite, siliceous and carbonate cements are key factors for the formation of low permeability reservoirs. The comprehensive analysis of molecular components, stable carbon isotope compositions of gases and light hydrocarbons indicated that the low permeability gases in the WSB are mainly coal-derived and can be divided into two types: (1) mature gases sourced from local coal-measure rocks in the Pinghu Formation, (2) exogenous highly mature gases sourced from the coal-measure rocks in the Pinghu Formation in the WSS. Mature gases were injected into the low permeability reservoirs in the middle-lower Pinghu Formation at approximately 2.8Ma∼0Ma. In the meantime, partial highly mature gases generated from source rocks in the WSS also migrated to the WSB. On the whole, the gas charge in the WSB is characterized by dual-sourcing and late-stage. The low permeability gases in the WSS almost are highly mature and composed of most coal-derived gases generated from local coal-measure rocks in the Pinghu Formation and a small amount of oil-derived gases generated from local dark mudstones containing sapropelic-type organic matters in the Pinghu Formation. In addition, mature coal-derived gases generated from source rocks in the lower Huagang Formation are also present but very limited. The charge of highly mature gases in the low permeability reservoirs in the lower Huagang Formation in the WSS occurred at approximately 3.9Ma∼0Ma.

Petrographic and stable isotopic evidences of CO2-induced alterations in sandstones in the Lishui sag, East China Sea Basin, China

Dawsonite-bearing sandstones in the Lishui sag, East China Sea Basin, China, have been investigated as a natural occurrence for CO2-induced diagenesis using petrography, X-ray diffraction and stable isotopes. The sandstones are predominantly litharenite, with the order of cements growth comprising clay coatings and pyriteⅠ, siderite, pyriteⅡ, quartz overgrowths, ankerite, kaolinite and microcrystalline quartz, dawsonite and late calcite. Dawsonite, which has recently been considered as trapping mineral after massive CO2 charging, constituted up to 7% of the whole rock volume, occurring as pore-filling clusters or replacement of detrital grains. Stable isotopic data suggest that the CO2 in equilibrium with dawsonite and calcite display a mantle-magmatic origin and is in close proximity to those of the CO2 gas now present in the reservoir, indicating the same origin for both. The elevated CO2 concentrations induced by a mass influx of magmatic CO2 into host rock was favourable for dawsonite cementation. Plagioclase was then considered as the precursor of dawsonite. K-feldspar could also serve as the aluminum source of dawsonite with an external supply of Na+ in a geochemically open system.

Preface: Evolution of the deep South China Sea: Integrated IODP Expedition 349 results

The offshore Chinese basins are located in the transition zone from the East Asia to the Western Pacific plate. The Cenozoic evolution of these basins reflects the geodynamic processes in East Asia. However, the coupling of the evolution of the offshore Chinese basins to the geodynamic processes occurring in the East Asian continental margin is still poorly understood. Here, the rifting processes of the offshore Chinese basins and the relationship between the basin evolution and the geodynamic processes of the East Asia Plate were analyzed using seismic data, fault activity, syn-sedimentary fault maps, and isopach maps. In the Offshore Bohai Bay Basin, the regional extension and local shearing occurred simultaneously. Accordingly, the regional NNW-SSE extension and local NNE-strike-slip shearing resulted in the NNE-striking graben-horst structure in the Liaodong Bay area while the NW-striking extensional faults and NNE-striking transtensional faults jointly control the structure of the Bozhong area. In addition, the NNE-striking branches of the Tan-lu Fault Zone led to the pull-apart structure in the Bonan area, and the NW-striking normal faults governed the half-graben structure in the Boxi area. Two stages of eastward movement of the rifting center in the East China Sea Basin were triggered by a change in the direction of subduction of the Pacific plate at ~43 Ma, and subduction of the Philippine Sea plate at ~20 Ma, respectively. In the South China Sea (SCS), Paleocene to E. Eocene initial extension occurred in the present northern and southern marginal basins of the SCS. Subsequently, the Ailao Shan Red River shear zone (ASRRSZ) traversed the eastern margin of the Indochina block, and pull-apart rifting dominated in the basins along this fault. Combined with the southward slab pull of proto-SCS and the strike-slip movement of ASRRSZ, sea floor spreading occurred, and the southern marginal basins drifted southerly and apart from the South China from 33 to 16 Ma.

Paleosalinity and water body type of Eocene Pinghu Formation, Xihu Depression, East China Sea Basin

Xihu Depression is a relatively new petroleum exploration area in East China Sea Basin. Pinghu Formation is one of the most important oil-bearing formations in the depression. Due to the low exploration level of the depression, paleosalinity and deposition environment of the depression in Pinghu stage is not clear. Element geochemical analysis of samples from different structural units is used to study ancient water salinity and reveal the depositional environment. B/Ga ratio, which is sensitive to paleosalinity in study area, is 0.9–4.0 and indicates characteristics of mixed water of fresh and salt water. There is a threshold for Sr/Ba in water salinity study in the study area. When Sr/Ba ratio is lower than 0.15, it cannot be used as an indicator for salinity and ancient water body type. Equivalent boron content calculated by Walker's method is lower than 150 ppm. Paleo salinity from boron content calculated by Couch's method is 2.97‰–9.61‰ and the average is 4.8‰. Based on the above mentioned results, ancient water body of Xihu Depression in Pinghu stage has typical characteristics of brackish water and it belongs to oligohaline and mesohaline water. Combining paleogeomorphology and sedimentary facies distribution in the study area, paleowater body in Xihu Depression during Pinghu stage is transitional mixed water influenced by terrigenous diluted water. Paleosalinity contour lines extend on plane from north to the south and are parallel to paleo-coastline. Paleosalinity increases from the west to the east. Influenced by freshwater of deltas at western part of the depression, high abnormal salinity values occur around the wells M1 and L1 where salinity contour lines curve westward.

Early Jurassic granitoids from deep drill holes in the East China Sea Basin: implications for the initiation of Palaeo-Pacific tectono-magmatic cycle

ABSTRACTThe timing of the Palaeo-Pacific Plate (PPP) subduction in East Asia, following the amalgamation of the North and South China Blocks (NCB and SCB), remains equivocal despite several investigations on the widespread subduction-related Mesozoic magmatism in this region. Here we report newly discovered granodiorites in the East China Sea Basin (ECSB) from deep boreholes (2945–2983 m), which yield SHRIMP zircon U–Pb age of 174 ± 1.1 Ma. The rock shows relatively high Sr/Y and La/Yb ratios, low contents of Ni, Cr, and MgO, and markedly negative values of εHf(t) (21.0 to −27.0). These geochemical and isotopic features are similar to those of the tonalite-trondhjemite-granodiorite (TTG) suites produced by the partial melting of the thickened lower continental crust. Our data, together with the ca. 190–180 Ma I-type granites reported from the eastern Zhejiang–Fujian and Taiwan areas, lead us to conclude that the continental crust in the coastal areas of South China underwent some degree of thickening during the Early Jurassic. A comparison with the coeval magmatic rocks in South Korea and Japan suggests that a large NE-trending continental arc (ca. 190–170 Ma) might have been constructed along the eastern margin of Asia at this time. Our study provides insights into the initiation of the Palaeo-Pacific tectono-magmatic cycle immediately following the consolidation of the SCB and NCB.

Geochemical characteristics of high-maturity crude oils in the Xihu Depression, East China Sea Basin

Geochemical characteristics of high-maturity crude oils in the Xihu Depression, East China Sea Basin

Improved Geometric Model of Extensional Fault‐bend Folding

AbstractExtensional fault‐bend folds, also called rollovers, are one of the most common structures in extensional settings. Numerous studies have shown that oblique simple shear is the most appropriate mechanism for quantitative modeling of geometric relations between normal faults and the strata in their hanging walls. However, the oblique simple shear has a rather serious issue derived from the shear direction, particularly above convex bends. We use geometric and experimental methods to study the deformation of extensional fault–bend folds on convex bends. The results indicate that whether the fault bends are concave or convex, the shear direction of the hanging wall dips toward the main fault. On this basis, we improve the previous geometric model by changing the shear direction above the convex bends. To illustrate basin history, our model highlights the importance of the outer limit of folding instead of the growth axial. Moreover, we propose a new expression for the expansion index that is applicable to the condition of no deposition on the footwall. This model is validated by modeling a natural structure of the East China Sea Basin.

Mitochondrial phylogeography of a surf clam Mactra veneriformis in the East China Sea: Genetic homogeneity across two biogeographic boundaries

Biogeographic boundaries constraining species' distributions often generate intraspecific ‘breaks’ for those species whose ranges span them—known as the ‘biogeography-phylogeography concordance’ hypothesis. The East China Sea (ECS) in the northwestern Pacific comprises two reported boundaries: the Shandong Peninsula and the Changjiang Estuary, providing an elegant setting to test the hypothesis in marine environment. Here we investigated population structure of the surf clam Mactra veneriformis (Reeve, 1854) using 235 individuals from its major distribution in the ECS, represented by mitochondrial cytochrome oxidase I sequences. A ‘star-like’ topology with shallow divergence was revealed for all haplotypes, of which the central (also assumed ancestral) one appearing in all populations. No significant genetic structure was revealed among populations, suggesting substantial genetic homogeneity across the range. Demographic expansion was revealed for individual and overall populations, and the expansion time was estimated from 23,000 years ago. These results suggested that the M. veneriformis populations originated from an ancestral panmictic population in the ECS basin, and had experienced significant population expansion since the last glacial maximum. From a mitochondrial view, the two boundaries did not act as barriers for the phylogeography of M. veneriformis.

The status of coastal oceanography in heavily impacted Yellow and East China Sea: Past trends, progress, and possible futures

Coastal environments are a key location for transport, commercial, residential and defence infrastructure, and have provided conditions suitable for economic growth. They also fulfil important cultural, recreational and aesthetic needs; have intrinsic ecosystem service values; and provide essential biogeochemical functions such as primary productivity, nutrient cycling and water filtration. The rapid expansion in economic development and anticipated growth of the population in the coastal zones along the Yellow and East China Sea basin has placed this region under intense multiple stresses. Here we aim to: 1) synthesize the new knowledge/science in coastal oceanography since 2010 within the context of the scientific literature published in English; 2) report on a citation analysis that assesses whether new research topics have emerged and integrated over time, indicate the location of modelling and field-based studies; and 3) suggest where the new research should develop for heavily impacted estuaries and coastal seas of East Asia. The conclusions of the synthesis include: 1) China has emerged as a dominant force in the region in producing scientific literature in coastal oceanography, although the area of publications has shifted from its traditional fields such as physical oceanography; 2) there has been an increasing number of publications with cross-disciplinary themes between physical oceanography and other fields of the biological, chemical, and geological disciplines, but vigorous and systematic funding mechanisms are still lacking to ensure the viability of large scale multi-disciplinary teams and projects in order to support trans-disciplinary research and newly emerging fields; 3) coastal oceanography is responding to new challenges, with many papers studying the impacts of human activities on marine environment and ecology, but so far very few studying management and conservation strategies or offering policy solutions.

Genesis, source and charging of oil and gas in Lishui sag, East China Sea Basin

Abstract Based on the results of components and stable carbon isotopic analysis of gas and oil from the Lishui sag, East China Sea Basin, the oil and gas genesis, source and charge process are studied by combining the history of structural evolution, oil and gas generation and migration and accumulation. The study shows that there are two types of gases in the Lishui sag now, one is the gas with high CO 2 content and low oil-type pyrolysis gas content found in Well WZ13-1-1, the other is the gas with high content of the mixture of coal-type gas and oil-type pyrolysis gas and certain content of CO 2 found in Well LS36-1-1, LS36-1-2 and LF-1. Hydrocarbon gases are all organic thermal gas, in which high maturity oil-type gas was from Paleocene Yueguifeng Formation and charged in middle-late Eocene-early Oligocene, and low maturity coal-type gas was from Paleocene Mingyuefeng Formation and was charged in late stage. The CO 2 in Well LF-1 is of organic origin, while CO 2 in other wells were derived from the deep inorganic mantle source gas charged variously in Oligocene. Oil in Well WZ6-1-1 is the high maturity sapropel type oil from Yueguifeng Formation which was charged in middle-late Eocene-early Oligocene. Condensate in Well LS36-1 is low maturity humus type oil from Mingyuefeng Formation charged in late stage. Oil in Well LF-1 may be of mixed source and greater proportion of oil likely from Paleocene Yueguifeng Formation.

Three-Dimensinal Structure Modeling of Lishui Depression, East China Sea Basin

Fine reservoir description plays an important role in oil and gas exploration and development, reservoir geological modeling is the core of fine reservoir description and the new technology developed in recent years of quantitatively characterizing reservoir as well. Petrel can be used to build three-dimensional visualization of quantitative reservoir by simulating and forecasting the reservoir characteristics and properties of parameters .And the reservoir unit is the targets of system modeling used to guide the re-awareness and tapping of the potential reservoir. This article describes three-dimensinal structure modeling of Lishui Depression East China Sea Basin with the help of powerful 3D visualization capabilities and integrated functional modules of the exploration and development, and results of case study show that the three-dimensinal structure model consists with its actual geological information, thus providing strong support for exploration and development of decision-making.

Genesis and maturity identification of oil and gas in the Xihu Sag, East China Sea Basin

Abstract Based on the composition and stable carbon isotope ratios of condensate and natural gas in the Xihu Sag, East China Sea Basin, origin and maturity of the hydrocarbon gas, CO2, N2 and condensate are determined using multiple methods. The CO2, low content of N2, condensate and hydrocarbon gas are mainly derived from thermal pyrolysis of coal-bearing measures. The relatively high content of N2 is collectively controlled by the thermal degradation of kerogen, vertical migration of gas and microbiological deterioration. Considering “evaporation fractionation” effect, a modified relationship between heptane and isoheptane has been used to calculate maturity of the condensate, which is in consistence with the results of the Mango method, i.e., the condensate is from mature source rock. The “two-segments of methane stable carbon isotopic fractionation model” has been used to calculate the hydrocarbon gas maturities. There are two mature stages of gas: one is mature gas which is equivalent to the condensate in maturity; the other is high maturity gas.

3D Visualization for Detailed Sedimentary-Facies Modeling of Lishui Depression, East China Sea Basin

Geological body is the product of the geological evolution in the time dimension and is also the record and the process of structural changes and sequence changes presenting in 3D configuration, so 3D visualization for sedimentary-facies modeling can results in a large quantity of spatial data which can be used for detailed sedimentary-facies modeling. Lishui Depression is taken for an example and the lower of Mingyuefeng Formation is the target formation for this study. Based on the analysis of sequence cycles and sedimentary environment and interpretation of 3D geological objects, the detailed 3D sedimentary-facies model for the lower Mingyuefeng Formation is built with Sequential Indicator Simulation. Then the 3D visualization of local sedimentary-facies is detailedly presented through fence models and profile models. The results prove that the methodology is competent for 3D modeling and self-adaptive visualization of large geological objects and it is a good way to solve the problem of integration and share of geological spatial data.