Petroleum System in Deepwater Basins of the Northern South China Sea

The northern South China Sea margin has experienced a rifting stage and a post-rifting stage during the Cenozoic. In the rifting stage, the margin received lacustrine and shallow marine facies sediments. In the post-rifting thermal subsidence, the margin accumulated shallow marine facies and hemipelagic deposits, and the deepwater basins formed. Petroleum systems of deepwater setting have been imaged from seismic data and drill wells. Two kinds of source rocks including Paleogene lacustrine black shale and Oligocene-Early Miocene mudstone were developed in the deepwater basin of the South China Sea. The deepwater reservoirs are characterized by the deep sea channel rill, mass flow complexes and drowned reef carbonate platform. Profitable capping rocks on the top are mudstones with huge thickness in the post-rifting stage. Meanwhile, the faults developed during the rifting stage provide a migration path favourable for the formation of reservoirs. The analysis of seismic and drilling data suggests that the joint structural and stratigraphic traps could form giant hydrocarbon fields and hydrocarbon reservoirs including syn-rifting graben subaqueous delta, deepwater submarine fan sandstone and reef carbonate reservoirs.

Seismic characteristics of a reef carbonate reservoir and implications for hydrocarbon exploration in deepwater of the Qiongdongnan Basin, northern South China Sea

Our analysis of approximately 40,000 km of multichannel 2-D seismic data, reef oil-field seismic data, and data from several boreholes led to the identification of two areas of reef carbonate reservoirs in deepwater areas (water depth >= 500 in) of the Qiongdongnan Basin (QDNB), northern South China Sea. High-resolution sequence stratigraphic analysis revealed that the transgressive and highstand system tracts of the mid-Miocene Meishan Formation in the Beijiao and Ledong-Lingshui Depressions developed reef carbonates. The seismic features of the reef carbonates in these two areas include chaotic bedding, intermittent internal reflections, chaotic or blank reflections, mounded reflections, and apparent amplitude anomalies, similar to the seismic characteristics of the LH11-1 reef reservoir in the Dongsha Uplift and Island Reef of the Salawati Basin, Indonesia, which house large oil fields. The impedance values of reefs in the Beijiao and Ledong-Lingshui Depressions are 8000-9000 g/cc x m/s. Impedance sections reveal that the impedance of the LH11-1 reef reservoir in the northern South China Sea is 800010000 g/cc x m/s, whereas that of pure limestone in BD23-1-1 is > 10000 g/cc x m/s. The mid-Miocene paleogeography of the Beijiao Depression was dominated by offshore and neritic environments, with only part of the southern Beijiao uplift emergent at that time. The input of terrigenous sediments was relatively minor in this area, meaning that terrigenous source areas were insignificant in terms of the Beijiao Depression: reef carbonates were probably widely distributed throughout the depression, as with the Ledong-Lingshui Depression. The combined geological and geophysical data indicate that shelf margin atolls were well developed in the Beijiao Depression, as in the Ledong-Lingshui Depression where small-scale patch or pinnacle reefs developed. These reef carbonates are promising reservoirs, representing important targets for deepwater hydrocarbon exploration. (C) 2008 Elsevier Ltd. All rights reserved.

Mineral provinces and matter provenance of the surficial sediments in the western Philippine Sea: implication for modern sedimentation in West Pacific marginal basin

The characteristics and distribution patterns of detrital minerals (0.063 similar to 0.125 mm) in marine sediments provide a significant indicator for the identification of the origin of sediment. The detrital mineral composition of 219 surface sediment samples was analysed to identify the distribution of sediments within the western Philippine Sea. The area can be divided into three mineral provinces: ( 1) province east of the Philippine Trench, the detrital minerals in this province are mainly composed of calcareous or siliceous organisms, with the addition of volcanogenic minerals from an adjacent island arc; (II) middle mineral province, clastic minerals including feldspar, quartz and colorless volcanic glass, sourced from seamounts with intermediate-acid volcanic rock, or erupting intermediate-acid volcano; (III) province west of the Palau-Kyushii Ridge, the matter provenance within this province is complex; the small quantity of feldspar and quartz may be sourced from seamounts or erupting volcano with intermediate - acid composition, with a component of volcanic scoria sourced from a volcano erupting on the Palau-Kyushu Ridge. it is suggested that, ( I) Biogenic debris of the study area is closely related to water depth, with the amount of biogenic debris controlled by carbonate lysocline. (2) Volcaniclastic matter derived from the adjacent island are can be entrained by oceanic currents and transported towards the abyssal basin over a short distance. The weathering products of volcanic rocks of the submarine plateau ( e. g. I Benham Plateau) and adjacent ridges provide an important source of detrital sedimentation, and the influence scope of them is constrained by the intensity of submarine weathering. (3) Terrigenous sediments from the continent of Asia and the adjacent Philippine island arc have little influence on the sedimentation of this study area, and the felsic mineral component is probably sourced from volcanic seamounts of intermediate-acid composition.

Carbonate cycle and its control factors in Kuroshio source region during the last 190ka BP

Two deep sea cores (Ph05-5, 16.05 degrees N, 124.34 degrees E, water depth 3382m and WP3: 22.15 degrees N, 122.95 degrees E, water depth 2700m) retrieved from the Kuroshio source region of the western Philippine Sea were selected to carry out the CaCO3 and calcareous nannofossil faunas study. Based on AMS(14)C data and comparing tire oxygen isotope curve with SPECMAP delta O-18 (Martinson et al., 1987) a stratigraphy was established. And, combining the changes of primary productivity and dissolution index of carbonate, the carbonate cycle and its control factors were analyzed in this region during the last 190ka BP. The carbonate contents showed higher values in the glacial periods and lower values during the interglacial and Holocene periods, which characteristics was similar to the tendency of "Pacific Type" carbonate cycle. However, there were high carbonate contents in the warm period and low values during the cold interval, which displayed the same tendency with the "Atlantic Type" carbonate cycle during the last glacial period (MIS4-2) in the east of Phillipines. The variations of primary productivity and carbonate dissolution index indicated that the carbonate dissolution was a major factor controlling the carbonate content in tire cast of Philippines, and the variations in carbonate contents were mainly affected by the productivity of calcareous organism in the Southeast of Taiwan. The "Atlantic Type" carbonate cycle in the cast of Phillipines during the last glacial period (MIS4-2) was an effect of the process of dissolution combined with the change of primary productivity.

Geochemical and isotopic characteristics of volcanic rocks from the northern East China Sea shelf margin and the Okinawa Trough

Volcanic rocks both from the northern East China Sea (NECS) shelf margin and the northern Okinawa Trough are subalkaline less aluminous, and lower in High Field Strength Elements (HFSE). These rocks are higher in Large Ion Lithophile Elements (LILE), thorium and uranium contents, positive lead anomalies, negative Nb-Ta anomalies, and enrichment in Light Rare Earth Elements (LREE). Basalts from the NECS shelf margin are akin to Indian Ocean Mid-Ocean Ridge Basalt (MORB), and rhyolites from the northern Okinawa Trough have the highest Pb-207/Pb-208 and Pb-208/Pb-204 ratios. The NECS shelf margin basalts have lower Sr-87/Sr-86 ratios, epsilon(Nd) and sigma O-18 than the northern Okinawa Trough silicic rocks. According to K-40-Ar-40 isotopic ages of basalts from the NECS shelf margin, rifting of the Okinawa Trough may have been active since at least 3.65-3.86 Ma. The origin of the NECS shelf margin basalt can be explained by the interaction of melt derived from Indian Ocean MORB-like mantle with enriched subcontinental lithosphere. The basalts from both sides of the Okinawa Trough may have a similar origin during the initial rifting of the Okinawa Trough, and the formation of basaltic magmas closely relates to the thinning of continental crust. The source of the formation of the northern Okinawa Trough silicic rocks was different from that of the middle Okinawa Trough, which could have been generated by the interaction of basaltic melt with an enriched crustal component. From the Ryukyu island arc to East China, the Cenozoic basalts have apparently increasing trends of MgO contents and ratios of LREE to Heavy Rare Earth Elements (HREE), suggesting that the trace element variabilities of basalts may have been influenced by the subduction of the Philippine Sea plate, and that the effects of subduction of the Philippine Sea plate on the chemical composition of basaltic melts have had a decreasing effect from the Ryukyu island arc to East China.

Isotopic feature and uranium dating of the volcanic rocks in the Okinawa Trough

Volcanic rocks from the northern and middle Okinawa Trough were dated by uranium-series dating method. Differential fractions using magnetic procedure were designed to separate samples. New report on the ages and isotopic data of rocks in the northern trough (especially black pumice) was discussed. Based on the uranium dates and Sr-Nd isotopic ratio, magmatic evolution process of the Okinawa Trough was noted. Firstly, there have been wide silicic volcanic activities in the Okinawa Trough from late Pleistocene to present, and the volcanic rocks can be divided into three subgroups. Secondly, magma generally came from PREMA source area under the Okinawa Trough. Magmatic evolution in the northern trough was similar to the middle, but different to the south. Finally, volcanic activities indicated that opening of the southern Okinawa Trough did not happen due to the collision between Luson Arc and Eurasian Plate until the early Pleistocene.

碳酸盐岩缝洞型储层地球物理响应特征及预测方法研究

Proven by the petroleum exploration activities, the karsts-fissure reservoir in carbonate rocks is significant to find out the large scale oil & gas field. They are made up of the four reservoir types: karsts-cave, karsts-crack, crack-cave and fracture-pore-cave. Each reservoir space and each reservoir bed has different features of reservoir heterogeneity and small scale of pore-crack-cave. The fracture-cave reservoir in carbonate rocks is characteristic by multi-types and long oiliness well. The reservoir shape is controlled by the irregular pore-crack-cave. The development level of fracture and karst-cave is the key element of hydrocarbon enriching, high productivity and stable production. However, most of Carbonate formation are buried deeply and the signal-ration-noise of seismic reflection are very low. It is reason why the fracture-cave reservoir are difficult to be predicted effectively. In terms of surveyed and studied lots of the former research outcome, The author applied the methods of synthetical reservoir geophysical prediction from two ways including macrosopic and microcomic technics in terms of the reservoir-cap condition, geophysics and geology feature and difficulty of prediction in carbonate rocks. It is guiden by the new ideas of stratigraphy, sedimentology, sedimentography, reservoir geology and karst geology. The geophysics technology is key technics. In aspects of macroscopic studies, starting off the three efficiencies of controlling the reservoir distribution including sedimental facies, karst and fracture, by means of comprehensive utilization of geology, geophysics, boring well and well log, the study of reservoir features and karst inside story are developed in terms of data of individual well and multiple well. Through establishing the carbonate deposition model, karstic model and fracture model, the macro-distribution laws of carbonatite are carried out by the study of coherence analysis, seismic reflection feature analysis and palaeotectonics analysis. In aspects of microcosmic studies, starting off analysis in reservoir geophysical response feature of fracture and karst-cave model according to guidance of the macroscopic geological model in carbonate reservoir, the methods of the carbonate reservoir prediction are developed by comprehensively utilization of seismic multi-attribution intersection analysis, seismic inversion restricted by log, seismic discontinuity analysis, seimic spectrum attenuation gradient, moniliform reflection feature analysis and multiparameter karst reservoir appraisement.Through application of carbonate reservoir synthetical geophysics prediction, the author r successfully develops the beneficial reservoir distribution province in Ordovician of Katake block 1in middle Tarim basin. The fracture-cave reservoir distributions are delineated. The prospect direction and favorable aims are demonstrated. There are a set of carbonate reservoir prediction methods in middle Tarim basin. It is the favorable basic technique in predicting reservoir of the Ordovician carbonate in middle Tarim. Proven by exploration drilling, the favorable region of moniliform reflection fracture and pore-cave and cave-fracture in lower-middle Ordovician are coincidence with the region of hydrocarbon show. It’s indicated that the reservoir prediction methods described in the study of Ordovician carbonate formation are feasible practicably.

塔克拉玛干沙漠地球化学研究

The Taklamakan Desert, lying in the center Tarim Basin of sourthern Xinjiang, is the largest sand sea in China and well known in the world as its inclemency. For understanding the formation and evolution of the Taklamakan Desert, it is very important to identify the provenance of aeolian sediments in the extensive dune fields, but the opinions from earlier studies are quite different. In this study, we examined the major- and trace-element compositions, mineral compositions and grain-size distributions of some Quaternary aeolian and nonaeolian sediments collected from the Taklamakan Desert, together with the variation of chemical and mineralogical compositions of different grain-size fraction. At the same time, we also studied the chemistries of some natural water samples (river water and groundwater) with the items of TDS, pH, Alkalinity, conductivity and major cation and anion compositions. Our results of analysis show some significant opinions as follow: Most of the frequency-distribution curves of grain size of dune sand samples are simgle peak, but that of the river and lacustrine sediment are most double peak or multi-peak. The grain-size distribution of dunefield sand changed gradually from north to south with the major wind direction in large scale, but there are many differences in regional scale. The major, REE, trace element compositions and mineral compositions are very different among the coarse, fine fraction and bulk samples due to the influence of grain-size. Most of the fine fractions are geochemically homogenous, but the coarse fractions and bulk samples are heterogenous. All the surface and ground waters are limnetic or sub-salty, their chemical compositions are mainly controlled by rock-weathering and crystallization- evaporation processes, and mainly come from the evaporate, while the contributions of the carbonate and silicate are little, excluding the influence on oasis water by carbonate. The mineral compositions of selected samples are stable, mainly composed of the strongly resistant mineral types. The mineral maturity of them are more immature at whole compared with other sandy sediments in the world, and they have experienced less degree of chemical weathering and recycling, being lying in the early stage of continental weathering. Among these sediments, the river sediments are relatively primitive. The sources of these sediments are maybe mainly terrigenous, silicic and subaluminous/ metalunious rocks, such as the granodiorite and its metamorphic rock. The geochemical compositions of dunefield sand are similar with those of the river sediments and dune sands near the river way; There are not only the resemblances but also the differences on geochemistry and granularity between north and south dunesands; The sediments from same section have different age but same trace-element compositions; The sediments from the south edge of Tarim Basin are all somewhat geochemically similar with the palaeo-river-sediment on the south edge of studying area. The REE data support the idea that the south dunesands are a little older than the north dunesands, and the tectonic settings of source area are mainly active continental margin based on the major-element compositions, so they indicate that the sediment of Taklamakan Desert maybe come mainly from the rock-weathering production of north part of the Kunlun Mountains. Compared with the sands of other dune field in north of China, the sands of the Taklamakan Desert are distinct by REE composition, but similar with the Luochuan loess, center China, and the two sandy dusts of Beijing, eastern China.

水利水电岩溶发育深度的定量化理论研究

The distribution in outcrop of carbonate rocks in China is about 3.44×106km2 and accounts for over one third of the total area of the country, mainly in the Yangtze valley and the Yungui tableland ,and there is a great plenty of Water and hydropower resources in these carbonate area. A large number of projects will be built in order to develop the Water and hydropower resources. They are facing amount of complicated problems of karsts, specially the problem of the depths of karsts below water, which is a key problem that hasn’t been solved well theoretically. So, systematically research in quantitative analysis of the problem is necessary, which is very important to solve the inconsistency between current theories and facts, and is helped to foresee the depth of karsts below water and decrease the expense of the engineering. For the problem mentioned above, the thesis makes a detailed research on the length of corrosion of karsts water, based on the kinetics of corrosion, and founds the primary theory about the processes of four typical geologic elements, which are single fracture, single conduit, porous limestone and fractured limestone. And it has done a deep research upon the characterties and kinetics of corrosion of the four typical geologic elements by simulation using the programme edited by the author. The thesis also makes a discussion on the general model and process of the form of caves by using the founded theory. According to the characteristic of Water Resource and Hydropower engineering, the thesis creates three representative flow-dissolution models for three types of common geologic conditions under the induction of the theory kinetics of corrosion of karsts water. It has done quantitative research upon the process of dissolution and brought out primary theory about quantitative analysis of the depth of karsts below water as well. It found that the depth of karsts below water relates to the specific geologic conditions and the time of dissolution by simulation based on typical parameters and deep analysis of the result. That is to say there are karsts caves in any depths in flow areas of groundwater in specific geologic conditions and appropriate time. The thesis also discourses three basic problems that frequently encountered in the reconnaissance of Water Resource and Hydropower engineering, which are karsts base level, essential conditions of karsts, the comparability of caves and terrace, and indicates the importance of time in karsts. Finally, as an application, the karsts of the scheming Qianzhong water resource engineering is analyzed by the primary theory founded of quantitative analysis. The result of the application comes to a conclusion that the theory accords with the facts properly.