Yinggehai Basin Gas Exploration: Comparison with Jiyang Depression

Transcription

1 Journal of Earth Science, Vol. 23, No. 3, p , June 2012 ISSN X Printed in China DOI: /s Yinggehai Basin Gas Exploration: Comparison with Jiyang Depression Zhifeng Wan* ( 万志峰 ) School of Marine Sciences, Sun Yat-Sen University, Guangzhou , China; Guangzhou Center for Gas Hydrate Research, Chinese Academy of Sciences, Guangzhou , China Bin Xia ( 夏斌 ), Baofeng Lü ( 吕宝凤 ), Zhourong Cai ( 蔡周荣 ), Weiliang Liu ( 刘维亮 ) School of Marine Sciences, Sun Yat-Sen University, Guangzhou , China ABSTRACT: Yinggehai ( 莺歌海 ) basin and Jiyang ( 济阳 ) depression experienced similar tectonic evolution, which is mainly controlled by the strike-slip faults. The strike pull-apart basins are characteristic by multiple deposition cycles, migration of deposition and subsidence center, and diversity depositional systems. Furthermore, both basins show abnormal formation pressure. Compared with the oil and gas-rich Jiyang depression, Yinggehai basin developed the similar geological background that is favorable to the formation of funnel-shaped meshwork-carpet subtle reservoirs. Overpressure diapir body is the core of hydrocarbon accumulation in central diaper zone of Yinggehai basin. Driven by high pressure, oil and gas migrate along the funnel-shaped passage system into the overlying low-potential zone formed. The overlying sand bodies of overpressure diapirs are the favorable gas exploration zone. KEY WORDS: natural gas exploration, subtle reservoir, Yinggehai basin, Jiyang depression. INTRODUCTION Yinggehai basin is one of the Cenozoic sedimentary basins in the northern South China Sea with a basin area of more than km 2 (Wu et al., 2009; He et al., 2008; Zhu et al., 2007; Gong and Li, 1997). One hundred years ago, many oil and gas seepages were found near the southwest coast of the Hainan Island. After systematic investigation from 1960s to 1990s, more than 100 oil and gas seepages were discovered This study was jointly supported by the National Basic Research Program of China (No. 2009CB219401) and the Guangzhou Center for Gas Hydrate Research, Chinese Academy of Sciences (No. CASHYD007s4). *Corresponding author: wanzhifeng01@gmail.com China University of Geosciences and Springer-Verlag Berlin Heidelberg 2012 Manuscript received August 3, Manuscript accepted December 30, and confirmed (Qiu and Gong, 1999; Li et al., 1998). Through half a century of oil and gas exploration, three gas fields and six gas-bearing structures have been found in the central diapir zone. Although that Yinggehai basin can form large oil and gas field has been confirmed, few great breakthroughs have been made in the oil and gas exploration in Yinggehai basin over the past decades. Therefore, more geological investigations in oil and gas geological features in Yinggehai basin need be carried out. It is important to compare some oil and gas-rich onshore basins, such as Jiyang depression, to establish overpressure basin hydrocarbon accumulation model and point out the exploration targets of Yinggehai basin. GENERAL GEOLOGY OF YINGGEHAI BASIN Yinggehai basin is a Cenozoic sedimentary basin developed along the suture belt between Indo-China and South China block (Lin et al., 2009; Zhong et al., 2004; Sun et al., 2003; Guo et al., 2001). Controlled

2 360 Zhifeng Wan, Bin Xia, Baofeng Lü, Zhourong Cai and Weiliang Liu by the NW, NNW, and SN basement faults, Yinggehai basin can be divided into four tectonic units: the central diapir zone, the Liangao swell, the Yingdong slope, and the Yingxi slope (Fig. 1). The central diapir zone developed and the area of the largest diapir body is more than 700 km 2 (Wang et al., 2004; Xie et al., 1999). The diapirs distribute in NW-SE direction, which can be divided into five rows with various shapes and sizes forming an echelon-shaped array diapir group. The anticlines that formed in the shallow mud diapir are potential gas trap. Red River fault zone o South China block 19 o 20 N Indo-China block Yingxi slope Lingao swell Yingdong slope No. 1 fault North bay Hainan Island DF1-1 DF29-1 Central diapir zone DF30-1 Coastline CN12-1 LD o Basin boundary Dirpic zone Fault CN18-1 LD14-1 LD13-1 LD15-1 LD20-1 LD28-1 LD o Figure 1. Tectonic zoning map of Yinggehai basin (modified from He et al., 2008; Zhu, 2007). 108 o E GEOLOGICAL COMPARISION OF JIYANG DEPRESSION AND YINGGEHAI BASIN Analogism has been widely used in the basin structure and hydrocarbon accumulation study. Through comparison between basins, comprehensive basin structure, sedimentary, and reservoir characteristics can be well understood, which is significant to oil and gas exploration in the low-degree basins (Xu et al., 2005; Gong et al., 2001; Qian, 2001). After nearly half a century of oil and gas exploration in Jiyang depression, more than 70 oil and gas fields have been discovered. It is a high degree of exploration area with 56.97% proven resources. During exploration research and practice, a series of new theories and new technologies are emerging and the old oil fields show a great exploration potential (Wang

3 Yinggehai Basin Gas Exploration: Comparison with Jiyang Depression 361 and Zhao, 2010; Zhang, 2006; Li and Pang, 2004). Although Yinggehai basin oil and gas were discovered early, few great breakthroughs have been made over the last 10 years (He et al., 2008; Zhu, 2007; Gong and Li, 1997). Comparing Yinggehai basin with Jiyang depression to find the common ground and learn from oil and gas exploration successful experience of Jiyang depression is significant to open up Yinggehai basin gas exploration new direction. o Formation Mechanism Comparison Formation mechanism of Jiyang depression The deposition and tectonic evolution of Jiyang depression is significantly controlled by the Tan-Lu strike-slip fault motion (Zhang et al., 2005; Wang Y et al., 2002; Wang X F et al., 2000; Zong et al., 1999). It has the general characteristics of the lithosphere edge strike-slip fault extensional rift basins (Zhou and Liu, 2006; Du et al., 1999; Wang et al., 1999). From Mesozoic to Early Paleogene (before 42 Ma), the Indian-Australian plate and the Yangtze plate moved north, while the Pacific plate subducted NNW, which caused the Tan-Lu strike-slip fault to move sinistrally (Fig. 2a). West of the Tan-Lu fault zone was sinistral shear stress field and developed a series of small rift basins (Hou et al., 2001, 1998; Zong et al., 1999; Wan, 1993). After 42 Ma, the Kula plate disappeared, the direction of the Pacific plate subduction changed from NNW to NWW. At the same time, the Indian plate collided with the Eurasian plate and put the NE compressive stress to the North China plate, which caused the Tan-Lu strike-slip fault to move dextral. Bohaiwan basin was in the dextral shear stretching stress field (see Fig. 2b) (Zhang, 2004; Hou et al., 1998). 50 N 30 o (a) 80 o 100 o 120 o 140 E 80 o 100 o 120 o 140 E Eurasian plate (b) Eurasian plate Tarim plate Altun fault Siberian plate Gansu-Qinghai- Tibet plate Xianshuihe fault North China plate Yangtze plate Pacific plate Indian-Australian plate Red River fault basin Bohaiwan Tan-Lu fault Tarim plate Altun fault Gansu-Qinghai- Tibet plate Siberian plate Xianshuihe fault North China plate Yangtze plate Pacific plate 30 N Indo-China plate Yinggehai basin South China Sea Indian-Australian plate Red River fault basin Bohaiwan Tan-Lu fault 10 o Indo-China plate Yinggehai basin South China Sea 10 o o Plate movement Fault Subduction fault Strike-slip fault Figure 2. Dynamic model of Tan-Lu and Red River faults. (a) Sinistral strike-slip; (b) dextral strike-slip (modified from Zhang, 2004; Guo et al., 2001; Tapponnier et al., 1982). Formation mechanism of Yinggehai basin Yinggehai basin lies in the suture belt between the Indo-China block and South China block (Red River fault), which is an extension of the Red River fault zone in the sea. Its formation and evolution are controlled by the activities of the Red River strike-slip fault (Zhu et al., 2009; Zhong et al., 2004; Sun et al., 2003; Guo et al., 2001). During Paleocene Early Miocene, the collision between the Indian plate and Eurasian plate caused Indo-China block clockwise extrusion southeast. The Red River strike-slip fault moved sinistrally (see Fig. 2a) (Zhong et al., 2004; Guo et al., 2001; Northrup et al., 1995; Tapponnier et al., 1982). In this NW sinistral strike-slip stress field, Yinggehai basin was opened. Normal faults developed and a series of half-grabens and echelon formed along the north-south trending faults. The basin was divided into

4 362 Zhifeng Wan, Bin Xia, Baofeng Lü, Zhourong Cai and Weiliang Liu several different structures units that controlled the sedimentary evolution. Influenced by mantle activities since ca. 5 Ma, the basin experienced long time rapid subsidence (Xia et al., 2006). Middle Miocene Quaternary, as India plate gradually wedged in Eurasian plate, South China block was extruded eastward, making the Red River fault converted to right-lateral strike-slip. Yinggehai basin was in a dextral pull-apart stress background (see Fig. 2b) (Fyhn et al., 2009; Sun et al., 2003; Li et al., 1998; Gong and Li, 1997), which led to the basin lithosphere stress state changed. Tectonic reversed in northern basin, the deposition center continued to move southeast and the axial of subsidence center changed to northwest, which is consistent with the current direction of the basin. Tectonic Evolution Comparison Tectonic evolution of Jiyang depression Impacted by the Tan-Lu fault, tectonic evolution of Jiyang depression consists of four stages: the initial rift (Mesozoic), fault (Paleocene Eocene; that is, Kongdian-the lower layer of second member of Shahejie (Ek Es 2L ) ground), fault-depression conversion (Oligocene, the upper layer of second member of Shahejie-Dongying (Es 2U Ed) ground), and depression (Neogene, Guantao (Ng), and above ground). At the initial rift stage, impacted by the Tan-Lu fault, Jiyang depression start to formed, which showed the massive tectonic pattern and accompanied with volcanic activity. In Paleogene rift stage, rift areas continued to expand with sediment filled fast and the subsidence center migrated southeast. Since Late Paleogene fault-depression conversion stage, the fault activity descended and the basin structure changed from the asymmetric half-graben to the near symmetry. The basin-fill mode transformed to overlap and the sedimentary environment changed from stable shallow lake to fluvial. At the depression stage, Jiyang depression subsided regionally and the original growth faults were no longer active. The deposition center disappeared and a unified large-scale depression formed. Tectonic evolution of Yinggehai basin Under the control of Red River fault movement, the tectonic evolution of Yinggehai basin consists of three stages: rift (Paleocene Early Oligocene), faultdepression conversion (Late Oligocene Miocene), and depression (Pliocene Quaternary). From Paleocene to Early Oligocene, Yinggehai basin was controlled by faulting and subsided with short-term high subsidence rate. From Late Oligocene to Miocene, the basin experienced rapid subsidence with long-term high subsidence rate. In Pliocene Quaternary, the basin underwent rapid subsidence with unobvious faulting process. The comparison of tectonic evolution between Yinggehai basin and Jiyang depression is shown in Table 1. Sedimentary Evolution Comparison Sedimentary evolution of Jiyang depression Under the control of Tan-Lu fault zone, Jiyang depression was reconstructed by the Yanshan movement, Jiyang movement, and Dongying movement after the Late Mesozoic. The characteristics of sedimentary evolution in Jiyang depression are as follows (Cao, 2003; Zhang, 2003; Wang and Qian, 1992). (a) Subsidence (deposition) center: The maximum subsidence center of Jiyang depression migrated from west to east and south to north. The subsidence center of Ek 1 -Es 4, Es 3 -Es 2, and Neogene Ng formations are located in Yangxin sag, Huimin sag, and Dongying sag and the northern of the depression, respectively. The deposition center is consistent with the subsidence center migrated from south to north. The main directions of sediment provenance for the basin are the east and west ends of the major axis. (b) Sedimentary cycle: The deposition of Jiyang depression consists of multi-sedimentary cycles. The climatic condition of the Ek 3 Ek 2, Ek 1 Es 4, Es 3 Es 2, and Es 1 Ed formations is warm and humid, arid, transformation from humid, conditions to the arid climate and humid, respectively (Wang and Qian, 1992). (c) Sedimentary system: A variety of sedimentary systems developed from south to north, meandering river delta system along the major axis of the basin, braided river delta system along the slope, fan delta and inshore subsea apron systems along the steep, shallow beach bar system, and central basin turbidite fan system (Deng et al., 2010).

5 Shahejie Yinggehai Basin Gas Exploration: Comparison with Jiyang Depression 363 Table 1 Comparison of tectonic evolution between Yinggehai basin and Jiyang depression Time Quaternary Pliocene Miocene Oligocene Age (Ma) Strata Quaternary Minghuazhen Guantao Dongying Jiyang depression Es 1 Es 2U Es 2L Es 3 Tectonic evolution Depression Fault - depression conversion Master fault Tan- Lu fault sinistral strikeslip Strata Quaternary Yinggehai Huang liu Meishan Sanya Lingshui Yacheng Yinggehai basin Tectonic evolution Depression Fault - depression conversion Master fault Red River fault sinistral strikeslip Red River fault dextral strikeslip Eocene Es 4 Rift Eocene Rift Paleocene Mesozoic Kongdian Paleocene Mesozoic Initial rift Tan- Lu fault dextral strikeslip Paleocene (d) Formation pressure: The abnormal overpressure is a common phenomenon in Jiyang depression, especially in Ed, Zhanhua, and Chezhen sags (Li et al., 2006; Liu et al., 2005; Xiao et al., 2003; Zheng et al., 2000). Vertically, the shallow reservoir pressure maintained in the hydrostatic pressure zone and the depth of overpressure formation is m in Dongying sag and Zhanhua sag and m in Chezhen sag. The highest pressure coefficient is 1.8. Plane and the overpressure layer mainly is below Es 3 or Es 4 mainly surrounding the subsidence and deposition centers. Sedimentary evolution of Yinggehai basin Yinggehai basin with thick sedimentary layer, the larger deposition-subsidence rate, deposition (subsidence) center migration, abnormal high temperature and pressure, and so on, has been the focus of attention of geologists (Sun et al., 2007; He et al., 2000; Zhang, 2000; Qiu and Gong, 1999; Gong and Li, 1997). (a) Subsidence (deposition) center: The subsidence corresponds to the tectonic evolution in Yinggehai basin. The first rapid subsidence occurred in Ma. The largest subsidence rate was up to 550 m/ma in northwestern basin and 700 m/ma in the center of the basin and the tectonic subsidence rate was up to 350 m/ma. Then, the subsidence rate decreased. During Ma, the subsidence rate was lowest. The second rapid subsidence occurred in Ma, and the maximum subsidence rate was up to 500 m/ma and tectonic subsidence rate was up to 150 m/ma. The third phase of rapid subsidence occurs at ca. 5.2 Ma, and the total deposition rate was up to 400 m/ma and tectonic subsidence rate was about 100 m/ma. Controlled by the Red River strike-slip fault, the deposition center of Yinggehai basin continued to move southeast during the development of the deposition process. The basin axis was in northwest direction before 36 Ma and changed to north-south axis later. The sedimentary basin axis returned to northwest direction gradually up to 21 Ma. (b) Sedimentary cycle: Four sedimentary cycles

6 364 developed in Yinggehai basin. Eocene-Yacheng with paralic depositional environment; Lingshui with coastal-shallow water depositional environment; Sanya-Meishan with neritic-bathyal depositional environment; and Huangliu-Yinggehai with shallow water-bathyal depositional environment (Xie et al., 2008). (c) Sedimentary system: Yinggehai basin developed three major sedimentary systems. Coastal plaincoastal-shallow marine depositional system; fan delta-shallow marine depositional system; and delta-bathyal depositional system composed of barrier bar, shallows, sand storm, shelf margin sand sheet, Zhifeng Wan, Bin Xia, Baofeng Lü, Zhourong Cai and Weiliang Liu turbidite deposit, delta, basin floor fan, slope fan, and other sand bodies (Li and Gao, 2010). (d) Formation pressure: The overpressure phenomenon is obvious in central diapir zone. Overpressure occurred in the Yinggehai formation depth less than m with formation pressure coefficient of a mutation up to 2.2. The formation pressure is normal in the Yingdong Slope with pressure coefficient between 1.0 and 1.2. The comparison of sedimentary evolution between Yinggehai basin and Jiyang depression is shown in Table 2. Table 2 Comparison of sedimentary characteristics between Yinggehai basin and Jiyang depression Comparison type Subsidence center Sedimentary cycle Sedimentary system Formation pressure Jiyang depression Migrated from west to east and south to north Four sedimentary cycles: Ek 3 Ek 2, Ek 1 Es 4, Es 3 Es 2, Es 1 Ed A variety of sedimentary systems: meandering river delta, braided river delta, fan delta, inshore subsea apron, shallow beach bar, turbidite fan The abnormally overpressure is more common in Ed, Zhanhua and Chezhen sags. The highest pressure coefficient is 1.8 Yinggehai basin Moved southeast gradually Four sedimentary cycles: Eocene-Yacheng, Lingshui, Sanya-Meishan, Huangliu-Yinggehai Three major depositional systems: coastal plain-coastal-shallow marine; fan delta-shallow marine; delta-bathyal The overpressure phenomenon is obvious in central depression zone. The highest formation pressure coefficient is 2.2 RESULTS OF THE COMPARISION BETWEEN YINGGEHAI BASIN AND JIYANG DEPRESSION Similarities between Yinggehai Basin and Jiyang Depression There are many similarities between Yinggehai basin and Jiyang depression that both basins belong to the strike pull-apart basins in the Eurasian plate margin. Yinggehai basin and Jiyang depression were controlled by large-scale after the first L-dextral strike-slip fault, which is related with Indian- Australian plate northward movement in a certain extent. The tectonic evolution experiences rift, rift-depression transform period, and depression phase of multiple deposition cycles. Deposition and subsidence centers migrate and diversity depositional systems developed. Furthermore abnormal formation pressure occurred widespread in the basins. Differences between Yinggehai Basin and Jiyang Depression Although Yinggehai basin and Jiyang depression experienced similar tectonic and sedimentary evolution, some obvious differences are recognized in the basins. Firstly, for the formation mechanism, although the basins are controlled by the strike-slip faults related to Indian-Australian plate moved northward, Jiyang depression was also affected by the subduction of the Pacific plate. Several tectonic inversion occurred, such as end of the Cretaceous, the late Ek, the late stage of Es 4 and Ed in Jiyang depression (Li et al., 2010). The formation of Yinggehai basin was also closely related to the expansion of the South China Sea (Xu et al., 2010). However, the formation mecha-

7 Computer software technology Temperature and pressure fields Connected sand body Yinggehai Basin Gas Exploration: Comparison with Jiyang Depression 365 nism of the South China Sea has been debated for decades, and its influence to the rift and tectonic inversion of Yinggehai basin is still unclear. Secondly, in the sedimentary characteristics, the deposition rate of Yinggehai basin is higher than Jiyang depression. Yinggehai basin consists of terrestrial deposit, marineterrestrial transitional deposit, and marine deposit, but Jiyang depression was major terrestrial deposit. The formation pressure mutated and rapidly increased in Yinggehai Formation due to higher deposition rate, but the formation pressure in Jiyang depression increased gradually and the pressure coefficient is smaller. Significance of Analogism The oil and gas exploration successful experience in Jiyang depression can be used to guide Yinggehai basin exploration due to the similarities of geological background between the basins. There are many new theories and new technologies after half a century of oil and gas exploration in Jiyang depression, such as source control theory (Hu, 1982); complex reservoir theory (Wang and Qian, 1992); complementation theory (Du, 2003); fault slope controlling sandbody, complex transporting system, and facies-potential-transport ternary reservoir model (Ma et al., 2009; Wang, 2007; Li and Pang, 2004; Li et al., 2003); geophysical prospecting, drilling, and logging; and many other interdisciplinary techniques for oil and gas exploration technology (Fig. 3). Subtle reservoir exploration theory Facies Potential Transport Sedimentary evolution Sedimentary facies Reservoir facies Tectonic belt Oil and gas potential Fracture surface Sequence boundary Sand prediction Evaluation of exploration directions Evaluation of exploration targets Subtle reservoir exploration technology High-precision threedimensional geotechnical Detailed seismic interpretation technology Three-dimensional visualization Logging constrained inversion Reservoir characterization techniques Supporting drilling technology Logging technology Reservoir protection and recognition Rolling development of subtle reservoirs Figure 3. Subtle reservoir exploration theory and technology diagram of Jiyang depression.

8 Huang liu Yinggehai Source rocks Seals 366 Therefore, the hydrocarbon exploration experience in Jiyang depression subtle reservoirs is useful reference to guide the gas accumulation in Yinggehai basin. The study of the unique overpressure characteristics will open up a new prospect for gas exploration in Yinggehai basin. FORMATION CONDITIONS OF SUBTLE RESERVOIRS IN YINGGEHAI BASIN Multiple Sets of Source Rocks Three sets of major hydrocarbon source rocks developed in Yinggehai basin (Fig. 4): Paleogene Zhifeng Wan, Bin Xia, Baofeng Lü, Zhourong Cai and Weiliang Liu mudstone (Eocene lacustrine hydrocarbon layer and Oligocene marine hydrocarbon layer, located in Liangao swell of the northwest basin); Neogene Lower Middle Miocene marine mudstone (Sanya and Meishan formations); and Neogene Upper Miocene Pliocene marine shale (Huangliu and Yinggehai formations). Neogene Lower Middle Miocene marine mudstone is the most important hydrocarbon source rocks in the basin, mainly distributed in the central diapir zone up to a maximum strata thickness of m with greater than 70% shales content. Lithology Chronostratigraphy Depth ( km) Reservoirs Seismic sequence boundaries Quaternary Neogene Paleogene Eocene Oligocene Miocene Pliocene U M L U M U M L Yacheng Lingshui Sanya Meishan Figure 4. Sedimentary characteristics and its relationship between source-reservoir-cap in Yinggehai basin (the profile is modified from CNOOC). The organic type is mainly II 2 III and the organic carbon content of the Huangliu and Meishan formations is between 0.39% and 2.60% with an average of 1.06% and between 0.44% and 3.17% with an average of 1.45%, which are good potential source rocks. The geothermal gradient of central diapir zone is /100 m. The depth of the organic matter maturation threshold is generally m, even shallow than m at some areas, corresponding to middle upper Yinggehai Formation (He et al., 2008; Zhu, 2007; Gong and Li, 1997). Diversity of Sedimentary Systems Formed Multiple Types of Reservoirs and Lithologic Traps There are three major sedimentary systems that consist of various reservoir sand bodies. The sand-

9 Pressure Yinggehai Basin Gas Exploration: Comparison with Jiyang Depression 367 stones in the central diapir zone are characteristics with fine grain size (mainly fine-very fine sandstone, some siltstone), high mature (high maturity-very high maturity), and high clay content usually between 7% and 17% and even up to 26% 38% in some layers. The reservoir space is mainly original intergranular pores in the shallow, and part of the secondary porosity, type of feldspar dissolution pores, intergranular dissolution pores, mold pores, matrix pores, and bio-dissolution pores. The main types of subtle traps in Yinggehai basin are as follows: 1 delta toe turbidite sandstone lithologic traps; 2 coastal sand traps; 3 basin floor fan, slope fan lithologic traps; and 4 basin floor channel sandstone of traps. A variety of reservoir type formed in the basin due to the deposition center transformation, eustatic sea level change, and multiple structural superposition, which provides the geological conditions of subtle traps formation. Delta, slump, turbidite, and other lithological traps mainly developed in the Dongfang zone. Basin floor fan lithologic traps are mainly located in the basin floor channel system in the Ledong dapir zone. Forced regressive dam and slope fan lithology traps developed in the upper of the basin. Abnormal High-Pressure Fluid Provided Channels and Dynamic for Gas Accumulation Many faults and fractures formed dues to the activity of abnormal high-pressure fluid in Yinggehai basin, which open up a vertical channel for natural gas migration (Jin et al., 2008; Yin et al., 2002; Hao et al., 1995). Because of many existing mud diapir strings, a crisscross of natural gas-channel network composed of a large number of longitudinal channels and the lateral reservoir pathway became an important factor for gas migration. While gas released from each diapir and diapir activity provides a powerful driving force for gas migration, the gas generated inside the diapir can not only be driven to the surrounding rock with low potential, but the gas near the diapir body also can be migrated even further. This provides the impetus for the gas migration and accumulation of the lithologic traps near the diapir zone (Fig. 5). T T30 T T41 Episodic evolution of fluid overpressure Open Emission Supply Fault Diapir body T Stratigraphic interfaces Pressure coefficient Close Act 1 Act 2 Act 3 Migration direction Figure 5. Overpressure fluid migration patterns of Yinggehai basin.

10 368 HYDROCARBON ACCUMULATION MODEL AND EXPLORATION DIRECTION OF YINGGEHAI BASIN Comprehensive analysis of Yinggehai basin and compared with Jiyang depression point out that Yinggehai basin has the similar geological setting for subtle reservoirs formation. The multiple sets of source rocks developed in multicycle sedimentary sequence, multiple types of reservoirs and lithologic traps due to the diversity of sedimentary system, and abnormal high-pressure fluid channels are favorable geological Zhifeng Wan, Bin Xia, Baofeng Lü, Zhourong Cai and Weiliang Liu conditions for gas accumulation. Five rows of high-pressure diapirs are mainly thick layer of mudstone sedimentary bodies developed in the central diapir zone. The overpressure formation is not only good source rocks but also an effective capping layer. Driven by the high-pressure fluid, natural gas migrates from diapir faults, sandstone, and unconformity to the low-potential areas around diapir body forming funnel-shaped meshwork-carpet reservoir (Zhang et al., 2008, 2003). Reservoir Diapir body Sedimentary body Fault Migration direction Figure 6. Funnel-shaped meshwork-carpet hydrocarbon accumulation model of Yinggehai basin. The funnel-shaped meshwork-carpet subtle reservoir model of Yinggehai basin (Fig. 6), overpressure diapir body, is the core of hydrocarbon accumulation. It is the hydrocarbon source rock, migration power source, and transporting network device. The geological background of rapid subsidence is not only the fundamental of overpressure but also the favorable source rock. Fluid energy accumulated in the closed sedimentary body pierce the overlying strata and form funnel-shaped fault system and microcracks, which became oil and gas transporting network. It is the bridge between source rocks and overlying sand body that improved the oil and gas transporting ability of thick mudstone overpressure. Overpressure diapir fluid is also a great power for oil and gas migration, effectively promoting oil and gas effective migration

11 Yinggehai Basin Gas Exploration: Comparison with Jiyang Depression 369 to the low-potential zone. Reservoir bodies overlying the diapir body, such as delta, fan delta, basin floor fan, turbidite fan, channel sand, and beach sand, connected by the diapiric faults and cracks, form the blanket type reservoirs. Based on the funnel-shaped meshwork-carpet subtle reservoir model and combined with geological background of Yinggehai basin, the overlying sand bodies of overpressure diapirs are the favorable gas exploration zone. CONCLUSIONS (1) The comparison between Yinggehai basin and Jiyang depression shows that they have many similarities: Both belong to the strike pull-apart basins in the Eurasian plate margin and controlled by strike-slip fault. The tectonic evolution experienced rift, rift-depression transform period, and depression. Both developed multiple deposition cycles. Deposition and subsidence centers migrated. Depositional systems were diversity. Both show abnormal formation pressure. (2) Compared with the oil and gas-rich Jiyang depression, Yinggehai basin developed the similar geological background of subtle reservoirs: the multiple sets of source rocks developed in multicycle sedimentary sequence, multiple types of reservoirs and lithologic traps due to the diversity of sedimentary system, and abnormal high-pressure fluid channels are favorable geological conditions for gas accumulation. (3) Put forward funnel-shaped meshwork-carpet subtle reservoir model of Yinggehai basins. Driven by high-pressure fluid, oil and gas migrate along the funnel-shaped passage system to the low-potential sand body overlying the diapir bodies and form the blanket-type reservoirs. The overlying sand bodies of overpressure diapirs are the favorable gas exploration zone. REFERENCES CITED Cao, Y. C., Research on Paleogene Sequence Stratigraphy and Genesis of Jiyang Depression: [Dissertation]. Graduate University of Chinese Academy of Sciences, Beijing (in Chinese Deng, H. W., Gao, X. P., Zhao, N., et al., Genetic Types, Distribution Patterns and Hydrocarbon Accumulation in Terrigenous Beach and Bar in Northern Faulted- Lacustrine-Basin of Jiyang Depression. Journal of Palaeogeography, 12(6): (in Chinese with English Abstract) Du, J. H., Subtle Reservoir Exploration of Erlian Basin. Petroleum Industry Press, Beijing (in Chinese) Du, X. D., Xue, L. F., Wu, G. H., Distribution of Mesozoic Basin and Discussion Geodynamics of Continent Interior in the Eastern China. Journal of Changchun University of Science and Technology, 29(2): (in Chinese Fyhn, M. B. W., Boldreel, L. O., Nielsen, L. H., Geological Development of the Central and South Vietnamese Margin: Implications for the Establishment of the South China Sea, Indochinese Escape Tectonics and Cenozoic Volcanism. Tectonophysics, 478: , doi: /j.tecto Gong, Z. S., Li, S. T., Dynamic Research of Oil and Gas Accumulation in the Northern Margin Basins of South China Sea. Science Press, Beijing (in Chinese) Gong, Z. S., Yang, J. M., Hao, F., et al., Difference in Natural Gas Accumulation Conditions between Yinggehai and Qiongdongnan Basins and Its Implications for Natural Gas Explotion. Earth Science Journal of China University of Geosciences, 26(3): (in Chinese with English Abstract) Guo, L. Z., Zhong, Z. H., Wang, L. S., et al., Regional Tectonic Evolution around Yinggehai Basin of South China Sea. Geological Journal of China Universities, 7(1): 1 12 (in Chinese Hao, F., Sun, Y. C., Li, S. T., et a1., Overpressure Retardation of Organic-Matter Maturation and Petroleum Generation: A Case Study from the Yinggehai and Qiongdongnan Basins, South China Sea. AAPG Bulletin, 79: He, J. X., Li, M. X., Chen, W. H., Geotemperature Field and Upwelling Action of Hot Flow Body and Its Relation with Natural Gas Migration and Accumulation in Yinggehai Basin. Natural Gas Geoscience, 11(6): (in Chinese He, J. X., Liu, H. L., Yao, Y. J., et al., Oil and Gas Geology and Resource Potential of Marginal Basins in Northern South China Sea. Petroleum Industry Press, Beijing (in Chinese) Hou, G. T., Qian, X. L., Song, X. M., The Origin of the Bohai Bay Basin. Acta Scientiarum Naturalium Universi-

12 370 Zhifeng Wan, Bin Xia, Baofeng Lü, Zhourong Cai and Weiliang Liu tatis Pekinensis, 34(4): (in Chinese with English Abstract) Hou, G. T., Qian, X. L., Cai, D. S., The Tectonic Evolution of Bohai Basin in Mesozoic and Cenozoic Time. Acta Scicentiarum Naturalum Universitis Pekinesis, 37(6): (in Chinese Hu, C. Y., Source Bed Controls Hydrocarbon Habitat in Continental Basins, East China. Acta Petrolei Sinica, 3(2): 9 13 (in Chinese Jin, B., Liu, Z., Li, X. S., Tree-Shaped Conducting Systems and Related Tree-Shaped Migration Model of Mud-Fluid Diapir in the Yinggehai Basin. Chinese Journal of Geology, 43(4): (in Chinese Li, P. L., Jin, Z. J., Zhang, S. W., et al., The Present Research Status and Progress of Petroleum Exploration in the Jiyang Depression. Petroleum Exploration and Development, 30(3): 1 4 (in Chinese Li, P. L., Pang, X. Q., Continental Rift Basin Subtle Reservoirs Formation A Case of Jiyang Depression. Petroleum Industry Press, Beijing (in Chinese) Li, S. L., Yu, X. H., Xie, Y. H., et al., Mud Flow Gully Identification Mark, Type and Depositional Model in the Littoral and Neritic Marine: A Case Study of Dongfang1-1 Gas Field in Yinggehai Basin. Acta Sedimentologica Sinica, 28(6): (in Chinese Li, S. L., Yu, X. H., Chen, J. Y., et al., Distributing Characteristics of Fluid Pressure in the Zhanhua Subbasin, Jiyang Depression, Bohai Gulf Basin, and Their Influence on Oil and Gas Accumulations. Journal of Geomechanics, 12(1): (in Chinese Li, S. T., Lin, C. S., Zhang, Q. M., et al., Episodic Rifting of Continental Marginal Basins and Tectonic Events since 10 Ma in the South China Sea. Chinese Science Bulletin, 43(8): (in Chinese) Li, W., Gao, R. S., Development Characteristics of Positive Inversion Tectonics and Its Controlling to Hydrocarbon Accumulation in Jiyang Depression. China Petroleum Exploration, 5: 17 24, doi: /jissn (in Chinese Lin, G., Peng, M. L., Zhao, C. B., et al., Numerical Analysis and Simulation Experiment of Lithospheric Thermal Structures in the South China Sea and the Western Pacific. Journal of Earth Science, 20(1): 85 94, doi: /s Liu, Z., Dai, L. C., Zhao, Y., et al., Characteristics of Geotemperature-Pressure Systems and Their Controlling Functions on Pools Distribution in the Jiyang Depression. Chinese Journal of Geology, 40(1): 1 15 (in Chinese with English Abstract) Ma, Z. L., Zeng, J. H., Wang, Y. S., et al., Connotation of Facies-Potential Coupling Effect on Reservoir in Jiyang Depression and Its Geological Significance. Acta Petrolei Sinica, 30(2): (in Chinese Northrup, C. J., Royden, L. H., Burehfiel, B. C., Motion of the Pacific Plate Relative to Eurasia and Its Potential Relation to Cenozoic Extension along the Eastern Margin of Eurasia. Geology, 23(8): Qian, J., Oil and Gas Fields Formation and Distribution of Subei Basin Research Compared to Bohai Bay Basin. Acta Petrolei Sinica, 22(3): (in Chinese with English Abstract) Qiu, Z. J., Gong, Z. S., China Oil and Gas Exploration (IV Offshore Areas). Geological Publishing House, Petroleum Industry Press, Beijing (in Chinese) Sun, Z., Zhong, Z. H., Zhou, D., The Analysis and Analogue Modeling of the Tectonic Evolution and Strong Subsidence in the Yinggehai Basin. Earth Science Journal of China University of Geosciences, 32(3): (in Chinese Sun, Z., Zhou, D., Zhong, Z. H., et al., Experimental Evidence for the Dynamics of the Formation of the Yinggehai Basin, NW South China Sea. Tectonophysics, 372: 41 58, doi: /s (03) Tapponnier, P., Peltzer, G., Le Dain, A. Y., et al., Propagating Extrusion Tectonics in Asia: New Insights from Simple Experiments with Plasticine. Geology, 10: Wan, T. F., Eastern China, the Cenozoic Intraplate Deformation of the Tectonic Stress Field and Its Application. Geological Publishing House, Beijing (in Chinese) Wang, B. H., Qian, K., Shengli Oil Geological Research and Exploration Practice. Petroleum University Press, Dongying (in Chinese) Wang, W. F., Lu, S. K., Jin, Q., Geodynamics of Sedimentary Basins in East China. Journal of the University of Petroleum, China, 23(4): 1 5 (in Chinese) Wang, X. F., Li, Z. J., Chen, B. L., Tan-Lu Fault Zone. Geological Publishing House, Beijing (in Chinese) Wang, Y. S., Study of Facies and Potential Coupling Ef-

13 Yinggehai Basin Gas Exploration: Comparison with Jiyang Depression 371 fect in Oil and Gas Pool Formation A Case Study in the Jiyang Depression, the Bohai Bay Basin. Petroleum Geology & Experiment, 29(5): (in Chinese with English Abstract) Wang, Y. S., Zhao, L. Q., Prospect Evaluation Approach and Application in Exploration Stage of Subtle Reservoir A Case of Jiyang Depression. Petroleum Geology and Recovery Efficiency, 17(3): 1 6 (in Chinese Wang, Y., Zhao, X. K., Gao, B. Y., Characters of Tectonic Evolution of the Jiyang Depression. Journal of Chengdu University of Technology, 29(2): l8l l87 (in Chinese with English Abstract) Wang, Z. F., He, J. X., Xie, X. N., Heat Flow Action and Its Control on Natural Gas Migration and Accumulation in Mud-Fluid Diapir Areas in Yinggehai Basin. Earth Science Journal of China University of Geosciences, 29(2): (in Chinese Wu, S. M., Qiu, X. L., Zhou, D., Crustal Structure beneath Yinggehai Basin and Adjacent Hainan Island, and Its Tectonic Implications. Journal of Earth Science, 20(1): 13 26, doi: /s Xia, B., Zhang, Y., Cui, X. J., et al., Understanding of the Geological and Geodynamic Controls on the Formation of the South China Sea: A Numerical Modelling Approach. Journal of Geodynamics, 42: 63 84, doi: /j.jog Xiao, H. Q., Liu, Z., Zhao, Y., et al., Characteristics of Geotemperature and Geopressure Fields in the Jiyang Depression and Their Significance of Petroleum Geology. Petroleum Exploration and Development, 30(3): (in Chinese Xie, X. N., Li, S. T., Hu, X. Y., et al., Transportation System and Its Information Mechanism of Hot Fluid in Diapir Belt, Yinggehai Basin. Science in China (Series D), 29(3): (in Chinese) Xie, X. N., Dietmar Müller, R., Ren, J. Y., et al., Stratigraphic Architecture and Evolution of the Continental Slope System in Offshore Hainan, Northern South China Sea. Marine Geology, 247: , doi: /j.margeo Xu, Y., Guo, W., Liu, L., et al., Comparison of Structures between the Qiangtang Basin, Northern Tibet, China, and the Tethyan Basin, Western Asia, and Their Petroleum Prospect Evaluation. Geological Bulletin of China, 24(6): (in Chinese Xu, Z. Y., Sun, Z., Zhang, Y. F., et al., Inversion Structures in the Northern Continental Margin of the South China Sea: Taking Lingao Uplift in the Yinggehai Basin and Qionghai Sag in the Pearl River Mouth Basin as Examples. Earth Science Frontiers, 17(4): (in Chinese Yin, X. L., Li, S. T., Yang, J. H., et al., Correlations between Overpressure Fluid Activity and Fault System in Yinggehai Basin. Geological Bulletin of China, 21(10): (in Chinese Zhang, M. Q., Migration-Accumulation Characterstics of Natural Gas in the Diaper Structure Belt of Yinggehai Basin. Journal of the University of Petroleum, China, 24(4): (in Chinese Zhang, Q., Jia, D., Chen, Z. X., et al., Relationship between Meso-Cenozoic Tectonic Subsidence of the Jiyang Depression and Plate Convergence Rate. Geological Journal of China Universities, 11(4): (in Chinese Zhang, S. W., Exploration Theory and Practice of the Tertiary Subtle Reservoirs in Jiyang Depression. Oil & Gas Geology, 27(6): (in Chinese with English Abstract) Zhang, S. W., Wang, Y. S., Peng, C. S., et al., Application of Fault-Fracture Mesh Petroleum Plays in Exploration. Acta Petrolei Sinica, 29(6): (in Chinese with English Abstract) Zhang, S. W., Wang, Y. S., Shi, D. S., et al., Meshwork- Carpet Type Oil and Gas Pool-Forming System Taking Neogene of Jiyang Depression as an Example. Petroleum Exploration and Development, 30(1): 1 10 (in Chinese Zhang, Y. Q., Late Cenozoic Squeezing-out Tectonism in Qinghai-Tibet Plateau and Its Impacts on Late Hydrocarbon Accumulation in Rift Basins in Eastern China. Oil & Gas Geology, 25(2): (in Chinese with English Abstract) Zhang, Z. L., Jiyang Paleogene Tectonic Features and Sedimentary Systems: [Dissertation]. Graduate University of Chinese Academy of Sciences, Beijing (in Chinese Zheng, H. R., Huang, Y. L., Feng, Y. L., Anomalous Overpressure System of Early Tertiary in Dongying Depression and Its Petroleum Geology Significance. Petroleum Exploration and Development, 27(4): (in Chinese

14 372 Zhifeng Wan, Bin Xia, Baofeng Lü, Zhourong Cai and Weiliang Liu Zhong, Z. H., Wang, L. S., Xia, B., et al., The Dynamics of Yinggehai Basin Formation and Its Tectonic Significance. Acta Geologica Sinica, 78(3): (in Chinese Zhou, L. Q., Liu, C. Y., Deep Fault and Cenozoic Basins in Eastern China Oil and Gas Resource Assessment. Petroleum Industry Press, Beijing (in Chinese with English Abstract) Zhu, M. Z., Graham, S., McHargue, T., The Red River Fault Zone in the Yinggehai Basin, South China Sea. Tectonophysics, 476: , doi: /j.tecto Zhu, W. L., Natural Gas Geology of Continental Margin Basins in Northern South China Sea. Petroleum Industry Press, Beijing (in Chinese) Zong, G. H., Xiao, H. Q., Li, C. B., et al., Evolution of Jiyang Depression and Its Tectonic Implications. Geological Journal of China Universities, 5(3): (in Chinese