| Fushan Sag is a typical rift lacustrine basin which is located at the southeastern margin of the Beibuwan Basin, and represtent complex fault blocks as an obvious feature caused by the frequent tecnotic activites since the Cenozoic. After more than 50 years’hydrocarbon exploration, the Fushan oil field has already become an essential part of the Beibuwan Basin. However, the pervious simple exploration mainly with structural traps can’t meet the current needs of the production of the petroleum industry, but the further subtle traps exploration has been seriously restricted by the complex fault blocks which contorl the depositional system of the basin. This paper using the geology, core, logging and high-resolution 3D seismic data which covers the whole study area, guided by the Sequence Stratigraphy, Sedimentology, Petroleum Geology and related theories, combining with the Basin Simulation, Seismic Sedimentology and some other techologies, based on the 3rd sequence stratigraphic framework, making the depositional system research of the Liushagang Formation as the main line, through the reaearch idea of "point-line-plane-body-time", combining with the dynamic and static, region and local analysis method, a systematic study of the Fushan Sag sedimentary facies types and characteristics, rebuilt the depositional enviroment and system space-time evolution characteristics. Finally we disscuss the distribution regularities of the lithologid reservoir under the sequence stratigraphic framework and realizes the structure-sequence stratigraphy-sedimentary-integration of the subtle reservoir prediction research.1. Beibuwan basin in the southeast margin of fushan sag in study area, the development of hainan uplift zone on the Northern Slope of a secondary rift type sag. Fushan sag according to the distribution calculation of paleogene system formation, sag of the total area of about 2920 km2, which located in the northern hainan Joan part uplift of the land area of 1900 km2, part of sea (less than 5 meters water depth) area of 140 km, the qiongzhou strait sea part 880 km (greater than 5 m). Sag in Cenozoic largest sedimentary thickness of about 9000 meters. Fushan sag has been rolling development farms oil and gas fields, white lotus oil and gas fields and oil field, oil and gas production are mainly concentrated in farms-white lotus area, accounted for 61.6% and 27.8% of fushan oil and gas production. Reservoir of this area are mainly distributed in the ancient system of quicksand port group and weizhou, quicksand port group is a deep lake, half deep lake facies clastic sedimentary, including quicksand layer has a port group as the main exploration, oil and gas production percentage is as high as 47.2%. Main exploratory well and appraisal well a total of 269, most of all have different levels of oil and gas shows.2. We can identify the braided river delta, fan delta and lake facies deposit, which were further divided into 7 phases and 17 sedimentary microfacies, using sedimentary structure, sedimentary sequence, granularity characteristics of core data of 42 important drilling in the different tectonic belt of Fushan sag and the electrical combination characteristics of logging data of 300 drilling in the whole study area, complemented by the regional sedimentary background, vertical sedimentary sequences and the symbiotic relationship of sedimentary facies. The vertical sedimentary filling sequences and superimposed relationship of single well were investigated, using Core, cuttings, drilling lithology, sedimentary facies, paleontology, and logging curve, complemented by all kinds of analysis, test, testing data of six representative drilling.3. On the base of Stratum Back Stripping Technology, the original basin geomorphology of an ancient certain period was restored by using the data of basin subsidence. Comprehensive analyses by combination of basin structure, sequence stratigraphy and sedimentary system, the pre-sedimentary paleogeomorphology of three members of the Paleogene Liushagang Formation were further confirmed. In order to characterize the resulting palaeogeomorphology more clearly, both the contour of palaeogeomorphology and 3D palaeogeomorphology were mapped by employing Discovery and Petrol model respectively. Overall, the paleogeomorphology relief presents features of multiphase changes that gullies and valleys were widely developed and sub-sags were separated strongly, during the deposition period of SQEls3 to SQElsl. Contrastive analysis of the subsidence rate and paleogeomorphology indicates that the subsidence center is coincidence with where both the subsidence rate and water depth of the sag are larger, while the relatively uplift zone is coincidence with where the subsidence rate is smaller. With the migration of the subsidence center, the depth center of the sag also migrated correspondingly. Based on the above analysis, five typical tectono-paleogeomorphology patterns were recognized.4. Adopting subsidence history analysis and tectonic geomorphology restoration, the provenance and depositional area were controlled roughly; using the seismic reflection characteristics analysis, the progradational directions of provenance towards the basin were described; utilizing the sandstone isopach and sand-stratum ratio contour maps, the branches of provenance were depicted. Consequently, provenance system characters of the Liushagang formation in Fushan Sag were analyzed and established accurately. Based on the seismic sedimentology research, eight kinds of main seismic facies were distinguished. The results of impendence inversion in the main seismic sections were refined by the restriction sparse pulse inversion method, then the seismic attributes (such as Variance Amplitude and CCP2) with six objective sequence boundaries were extracted, and finally four provenance system of Liushagang formation in the study area were confirmed by the corresponding relationship between the geologic information and the warm color and higher value area of seismic attributes:Hainan Uplift provenance area in the south, Linggao Uplift provenance area in the west, Yunlong Uplift provenance area in the east and the northern provenance area.5. Through the sequence stratigraphic framework of the constraints, According to "points-lines-systems-time" thinking, base on the core observation and single well sedimentary micrfacies research, selected seven NS direction, three WE direction 2d level profiles which cover whole research area to contrast from well to well and Combined with the feature of seismic facies in the same sequence divide sedimentary facies, sub facies and microfacies, then analyse sandstone distribution characteristics in the profile.this means different from traditional sand body comparison method which relys on "coarse correlation coarse and fine correlation fine" The concrete research content has the following four aspects:1) Through the 3d seismic reflection characteristic analysis provenance system characteristics of each sequence and sedimentary facies distribution direction, and the determination of the flooding surface; 2) Through slope angle and fracture occurrence analysis the connected and blocked characteristics of system tract sand body; 3) core and single well sedimentary microfacies analysis project to sand body to inspect sedimentary facies and microfacies types; 4) Set up sedimentary system well-connecting profiles under the sequence stratigraphic framework, and horizontally contrast and relaze close of correction well-connecting profiles. Elaborately carve the same sedimentary profiles of mainly tectonic belt in sag, to provide sufficient evidences for the plane distribution sedimentary system researchs.6. Rebuilt the depositional system of Liushagang Formation in Fushan Sag, then analysis the plane distribution features of each 3rd sequence unit, following conclusions have been found:1) during the SQEls3 period, the Fushan Sag was still in the early chasmic stage which coming with gradually development of tecnotic acvitites, basin extension and the water level change ddeeply, and still with abundant deposits feed. However, because of the extension of basin, the centre region represented as under-compensation deposition. Also obvious change has happened on the depositonal system as an important transformation from alluvial river in SQEch to lacustrine facies; 2)during the SQEls2 period, the basin came into the reginal transgression period and rapidly extend, impacting by strong activites of the Meitai Fault and rapidly subsidence, which fainlly caused the lacustrine facie to be the dominant depositional environment; 3) during the SQElsl period, Fushan Sag got another abundant deposits supply generated with the greatly uplift of the Hainan Uplift, which caused broad denudation areas around the Southern Slope Zone and obviously migration of the whole depositional system.7. delicately depicted the spatitiotemporal evolution characterse and sedimentary mode of different sedimentary systems in Fushan Depression. 1)The fan dalta mainly developed in SQEls2 formation and SQElsl formation, distributing at the downthrown side of Lingao fault in the west and Changliu fault in the east, as well as the steep slope zone controlled by fault in Huachang secondary bulge in the central section. The characteristic of fan dalta plain subfacies is not obvious, the facies distributed narrowly, While neritic subaqueous fan developed at the downthrown side of steep slope zone in Huachang secondary bulge in the central section. For it is the second sedimentation that the north source transferred to Huachang secondary bulge, the clastic particles are finner than the fan dalta in the basin margin with a small scale.2)The braided fan dalta front deposit is the most active part in Liushagang formation, the asymmetric rift basin resulted by the degree difference of steep slope, made the delta north-south sub-zone and east-west subsection,4 sets of lake basin water systems injected from the south of the depression developed successively four delta sand body.3)Based on the division of 4 kinds of gravity current lithofacies types, through the contrastive analysis of section well and sand layer characteristic in large-scale, two main association lithofacies types are put forward, the west developed sublacustrine fan deposit which consists of turbidite current, while the east developed sandy slump and sandy debris flow.8. Analyze the main control factors on the depositional system:1) depositional process is closely related to tecnoic activites. During the SQEls3 period, widely developed over the study area of the LST-EST-HST period due to settlement and extend the sedimentation of strengthen at the same time; During the SQEls2 period, the basin get strong subsidence and came into the EST period which bring out huge thick clay stone; During the SQElsl period, the tecnoic activites get weaker which cause small lowstand system tract development around the eastern slope area.2) application of Petrel three-dimensional modeling software of palaeogeomorphology and sedimentary system distribution, coupling analysis to analyze the ancient landform and depositional systems and the matching relation between the coupling laws; 3) reveal the ancient landscape, sequence style and sedimentary system coupling relationship:acceptor fushan sag tectonic belt, the control of its shape presents the long and short axis, the formation of the longitudinal and transverse different depositional systems. Edge of the basin slope break belt type control delta plane distribution form, in the short axis direction of lake basin, the steeper the slope, transverse distribution of the sediment in the limit, the wave action transformation is stronger; Whereas slope is slow, sediment distribution range is wide, the wave action weaker, the role of the river is stronger; 4) sequence at different time domain (system) in the delta also presents different sedimentary characteristics, such as SQElslLST period due to the lake water body is relatively low, lake shoreline migration direction, multidirectional basin in southern slope belt to the braided river delta basin into the clear, sediment moving far away to the lake, river channel is stronger, the effect of delta bird’s foot in shape distribution. And SQEls1HST period, due to the shoreline change smaller, water level is higher, the southern slope belt overall accretion and braided river delta prograde is given priority to, formation and evolution of the wave impact together with river delta, delta shape usually have a leaf.9. Through the research of hydrocarbon accumulation conditons and regularity under a sequence stratigraphic framework of Fushan Sag Liusha formation, this paper sums up the trap type and accumulation model of the main hydrocarbon reservoirs in the area, and predicting four trap of the main hydrocarbon reservoirs:1)Hua Chang second uplift tectonic transform belt; 2)Huang Tong deep sag in the west; 3)Sandy debris flow deposits of Bai Lian second sag and steep slope belt of fault control of Yun Long uplift in the east.4) steep slope belt of fault control of Lin Gao uplif. This will service the subtle reservoir exploration of Fushan sag, rich the oil and gas exploration theory of continental basin, and has the reference significance to the oil and gas exploration research of many of the continental fault basin of the same background in eastern China. |
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