Table of Content

25 February 2004, Volume 25 Issue 1

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Concept and appraisal principles of hydrocarbon preservation unit

He Dengfa, Ma Yongsheng, Yang Minghu

2004, 25(1):  1-8.  doi:10.11743/ogg20040101

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A thorough understanding of seals is needed for petroleum exploration in marine carbonate strata in Tarim basin, Ordos basin and southern China. A concept of ″petroleum preservation unit″ is presented. It is a petroliferous geological unit with fluids being sealed in 3D space within a sedimentary basin. According to their spatial structures and evolution in geologic history, hydrocarbon preservation units can be classified into three basic types,succession,modification and reconstruction types.Hydrocarbon preservation unit can be delineated based on analysis of cap rocks, sealing capacity and sealing time of faults,as well as some key events,such as volcanic activities, earthquake and hydrogeological process.In combination with the study of basin and petroleum system,pool-forming elements and processes can further be analysed,and comprehensive evaluation of hydrocarbon preservation units can then be made.In the case of Chuxiong basin,seven hydrocarbon preservation units have been analyzed and evaluated,and Dongshan,Zhonghe-Dayao and Yongren have finally been selected to be the three favorable hydrocarbon preservation units.

Physical properties and genesis of oil in Shengtuo oilfield in Jiyang depression

Zhu Guangyou, Jin Qiang, Zhou Jianlin, Wang Tongshan, Li Jian, Zhang Linye

2004, 25(1):  9-13.  doi:10.11743/ogg20040102

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Crude oil in Shengtuo oilfield in Dongying depression can be classified into heavy oil and normal light oil according to their physical properties.The former,accumulated in shallow reservoirs,are the result of secondary modification of low-maturity oil generated from the source rocks in the 4th member of Shahejie Formation;while the latter,accumulated in deep lithological and structural-lithological reservoirs, have high maturity. They can also be divided into three types according to their sulfur content.Oil with high sulfur content are distributed in shallow reservoirs and generated from source rocks deposited in salt or saline lake in the 4th member of Shahejie Formation; oil with low sulfur content are distributed in the deep 3rd member of Shahejie Formation and are generated from source rocks deposited in freshwater-brackish lake in the 3rd member of Shahejie Formation;while oil with medium sulfur content have mixed sources.Therefore, sulfur content can be used as an effective index for oil source correlation.

Classification of overpressure systems in sedimentary basins and their relationship with hydrocarbon migration and accumulation

Sun Dongsheng, Jin Zhijun, L? Xiuxiang, Yang Minghui, Zhou Xinyuan

2004, 25(1):  14-20,38.  doi:10.11743/ogg20040103

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Based on locations of source rock and key factors controlling genesis of overpressure systems,overpressure systems in sedimentary basins can be classified into deep overpressure system and shallow overpressure system.The former have mature to overmature source rocks,and overpressure is widely distributed,especially in Meso-Cenozoic basins;while the later lack of mature source rock,and the distribution of overpressure zone is generally limited in foreland basins,i.e.dual overpressure system occurs in foreland basins.Based on the analyses of generation and sealing of hydrocarbons in deep overpressure system,it is believed that hydrocarbon generation would be the primary factor controlling overpressure systems,while others are only secondary factors that further increase formation pressure.The upper overpressure system has been formed as the result of late tectonic compression on the basis of early normal pressure reservoirs.Correct discrimination of the two types of overpressure systems is essential to the study of hydrocarbon generation,migration and accumulation.Deep overpressure system is especially important to petroleum exploration, as it is the"chemical reaction furnace"of hydrocarbon generation,provides the original power for hydrocarbon migration,and determines the phase state and mode of migration and characteristics of accumulation.Generally,hydrocarbons would be difficult to accumulate in deep overpressure system.However,hydrocarbon accumulations can be formed in overpressure system when the original balance of temperature and pressure is broken due to structural uplifting or faulting.

Kinetic study of carbon isotope in humic gas methane in Kuqa depression

Li Xianqing, Xiao Xianming, Tang Y, Mi Jingkui, Shen Jiagui, Xiao Zhongyao, Bao Jianping, Xiong Bo

2004, 25(1):  21-25.  doi:10.11743/ogg20040104

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The characteristics and kinetic modeling of carbon isotope of methane in Jurassic humic gas in Kuqa depression in Tarim basin have been studied by combining pyrolysis experiment in closed gold tube system and analysis of methane isotope with GC-IRMS isotope mass spectrograph.The carbon isotope ranges between -3.6%～-2.5% and is closely related to pyrolysis temperature (or vitrinite reflectance Ro) and heating rate. Kinetic simulation results of carbon isotope in humic gas methane are in good agreement with the experimental data, thus the experimental data can be extrapolated through kinetic modeling and applied to actual geological conditions. Simulation results show that natural gas in Kela 2gas field in Kuqa depression has mainly experienced episodic accumulation since 10 Ma (especially 5 Ma).

Flow unit study at middle and late development stages in Northern Dagang oilfield

Dou Songjiang, Yu Xinghe, Li Caixiong

2004, 25(1):  26-30.  doi:10.11743/ogg20040105

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Taking the Paleogene fluvial reservoirs in Gangdong area in Northern Dagang oilfield as an example, the reservoirs in Gangdong area can be divided into 118 time-stratigraphic units vertically and 2681oil-bearing sandbodies laterally based on fine reservoir correlation and study of reservoir structure and flow barriers. Totally 9000 flow units are defined by using factorial analysis method according to the spatial distribution of physical properties of each sand body and the dynamic analysis data. Numerical modeling and conventional reservoir engineering methods have further been used to progressively determine the quantities of the remaining oil potential in each flow unit and define 6 types of remaining oil potentials. Areas with remaining oil potentials that have been formed due to imperfect flood pattern, the difference of producing status between various vertical flow units,and the impacts of flow barriers and microstructures are the main targets of development in the future.

Oil and source correlation in Lunnan and Tahe heavy oil fields

Ma Anlai, Zhang Shuichang, Zhang Dajiang, Jin Zhijun

2004, 25(1):  31-38.  doi:10.11743/ogg20040106

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Several technologies, including GC,GC-MS,GC-MS-MS,match experiment and ruthenium ion catalytic oxidation of asphaltenes,are used to study the sources of heavy oil in Lunnan and Tahe oilfields, Tarim basin. The heavy oil in Lunnan and Tahe oilfields contain 25-norhopane, while the distribution of normal paraffin hydrocarbons is complete and chromatographic base lines are uplifted in varying degrees,showing that the accumulations have been formed in two stages. The heavy oil are characterized by high content of tricyclic terpane, low content of C₂₄ tetracyclic terpane, gammacerane, C₂₄ sterane, triaromatic sterane, 4-methyl cholestane-24-ethyl cholestane, aromized sterane,and 24-norsterane. Oil and source rock correlation indicates that the oil in Lunnan and Tahe oilfields come from the source rocks in Middle and Upper Ordovician. Match experiments show that the oil would have also the characteristics of Cambrian source rock if it is mixed with 25% of TD2well's oil generated from Cambrian source rock,indicating that the hydrocarbons generated from Cambrian source rocks have not extensively migrated into Lunan and Tahe reservoirs. Ruthenium ion catalytic oxidation of asphaltenes further verifies that the source rocks in Middle and Upper Ordovician are the main source rocks of heavy oil in Lunnan and Tahe oilfields.

An analysis of oil-source characteristics of central uplift belt in Dongying depression

Liu Hua, Jiang Youlu, Yang Wanqin, Wang Ning

2004, 25(1):  39-43.  doi:10.11743/ogg20040107

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Source rocks in E_s3 (the third member of Shahejie Formation) in Dongying depression are characterized by the predominance of pristane with a pristane/phytane ratio of 0.5～1.0 and small amount of gammacerane; while source rocks in E_s4 (the fourth member of Shahejie Formation) are characterized by the relative abundance of phytane with a pristane/phytane ratio of below 0.5 and rich in gammacerane.Based on this remarkable difference, the oil sources of oilfields in the central uplift belt of Dongying depression are classified into E_s3, E_s4 and mixing types,of which the E_s3 and mixing types are predominant. Sources of oil in different regions and different horizons vary greatly. Study on structural features and areal distribution of geochemical properties reveal that the hydrocarbons would migrate preferentially into the nearest reservoirs, thus the center of each sag consists of the center of oil source.The oil in the western area come mainly from the E_s3 source rocks in Lijin sag; small amount of oil in the southeastern area come from the E_s4 source rocks in Niuzhuang sag;while oil in the northeastern area have been generated by the source rocks in Minfeng sag. Oil of mixing type commonly occur in areas where faults are well developed, indicating that faults have large impacts on mixing type oil.

A study on geochemical characteristics and sources of oil produced from Wengu 2well in Wenliu buried hill in Dongpu depression

Chang Junhe, Li Xinjun, L? Hongyu, Wang Youjie, Sun Qing, Duan Hongmei

2004, 25(1):  44-48,69.  doi:10.11743/ogg20040108

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Oil source correlation is one of the important methods to trace new oil layers and guide exploration. Based on analysis of geochemical behaviors of oil produced from Wengu 2well, correlation of crude oil and potential source rocks has been made through comparing carbon isotopes and biomarkers in combination with the regional geologic setting.As for the crude oil in Wengu 2well, hydrocarbon content is high,while nonhydrocarbons + asphaltenes content is low in its group components; the δ¹³C in the components and whole hydrocarbon is light;the main peak's carbon is nC 17; and gammacerane and oleanane are abundant. Oil-source correlation indicates that the Wengu 2well buried hill reservoir belongs to young source rock and old reservoir rock type,and the Paleogene mudstone is the main source rock.The crude oil and the extract from Paleogene dark-colored mudstone have very similar δ¹³C value and distribution,and both of them have high gammacerane and oleanane contents. The extract from coal-measure source rock and simulated oil have large δ¹³C value, low gammacerane content and no oleanane,significantly different from the crude oil in Wengu 2well.

Reverse structures and their impacts on hydrocarbon accumulation in Songliao basin

Hou Guiting, Feng Dachen, Wang Wenming, Yang Mohan

2004, 25(1):  49-53.  doi:10.11743/ogg20040109

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Reverse structures in Songliao basin are mainly wide and gentle folds and placanticline with small deformation.The reverse structures have been formed in three differant stages:at the end of deposition of Nenjiang Formation in Late Cretaceous,at the end of deposition of Mingshui Formation and Late Cenozoic.The strongest reverse structural action that occurred at the end of deposition of Nenjiang Formation would have the largest effect on hydrocarbon accumulation in Songliao basin,including (a) reverse structures provide traps for hydrocarbon accumulation; (b) reverse structural actions promote remigration of hydrocarbons; and (c) reverse structures result in many fractures and thus improve the poroperm characteristics of reservoir rocks.

Evolution of superposed Jurassic and Cretaceous basins in Beishan-Alxa area

Li Mingjie, Zheng Menglin, Cao Chunchao, Zhang Junyong

2004, 25(1):  54-57.  doi:10.11743/ogg20040110

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The Jurassic basins in Beishan-Alxa area have been controlled by near EW-trending faults and can be divided into Alxa and Mongolia orogenic belt two sedimentary provinces.The Jurassic basins in Mongolia orogenic belt can be subdivided into Heiyingshan-Ejinaqi and Gongpoquan-Zhongkouzi-Suhongtu (Shangdan) sedimentary zones.They have smaller areas than those in Alxa sedimentary province and have experienced stronger epigenetic deformation.The Early Cretaceous basins,controlled by NE-trending faults,are faulted lake basins separately distributed in NE direction in the shape of half graben or asymmetric faulted basins. They can also be divided into two sedimentary provinces,Alaxa and Mongolia orogenic belt.A set of very good source rocks have been developed in Mongolia orogenic belt,and a set of clastic rocks rather than source rocks have been developed in Cretaceous basins in Alaxa block. The Jurassic and Cretaceous basins superpose in high angles. There exists two superposition patterns,cross superposition and drape superposition,and the latter is favorable for the early burial and maturation of source rocks in the basin.Therefore it is a favorable exploration area.

Detached deformational salt structures and the significance in petroleum exploration in Dongpu depression

Hou Yanping, Sun Xiangyang, Ren Jianye

2004, 25(1):  58-61.  doi:10.11743/ogg20040111

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Thick salt deposits were developed in Paleogene in the northern Dongpu depression. Under sustained stretching stress, extensional forced folds were formed in the overlying formations of salt beds due to their differential subsidence.At the same time, continuous down-tilting of the secondary fault blocks in the underlying formations resulted in increasing of downslide shear stress and even exceeding the shear strength of salt beds, thus listric detached faults were formed in the overlying beds,and rollover anticlines were formed in the upper wall of salt detached faults. The detached deformational salt structures would not only constitute good migration pathway but also provide various traps for hydrocarbon accumulation,such as oil and gas reservoirs in fault block traps, extensional forced fold traps, rollover anticlinal traps, traps in the footwall of the detached faults and reverse drag fault traps in Dongpu depression. The development of detached deformational salt structures led to the formation of hydrocarbon enrichment in the central uplift zone of Dongpu depression

Types and features of source-reservoir-cap rock combinations in Paleozoic sequence in southern China

Chen Hongde, Qin Jianxiong, Tian Jingchun, Zhou Yan

2004, 25(1):  62-69.  doi:10.11743/ogg20040112

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In view of status of petroleum exploration in marine carbonates in southern China,a dynamic and practical classification scheme is presented for source-reservoir-cap rock combinations based on sequence stratigraphy study. It divides, for the first time, the source-reservoir-cap rock combinations in this region into 5 types,including boundary type, low water type, transgression type, high water type and composite type.Various types of combinations have different sedimentary and geological features and different petroleum geological significances. The boundary type is characterized by poor effectiveness in timing; the low water type is characterized by its wide distribution,small reservoir bodies and optimum migration conditions; the transgression type has strong sealing capability with small reservoir bodies; the high water type is rich in petroleum and is characterized by its largest reservoir bodies,widest distribution and regional and even globel comparability; while the composite type is characterized by its large, wide and stable distribution and hydrocarbon accumulations of multiple sources,multiple stages and multiple geneses.

Tectonic stress field modeling and fracture prediction in T₃χ^2-4 strata in Xiaoquan-Xinchang area, western Sichuan depression

Zhang Shouren, Wan Tianfeng, Chen Jianping

2004, 25(1):  70-74,80.  doi:10.11743/ogg20040113

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Elastic-plastic incremental modeling of tectonic stress field is to approximate parabolic stress-strain curves with several linear portions and perform elastic modeling with finite element method in each linear portion. It is applied to perform numerical simulation of the tectonic stress field in T₃x^2-4 strata in Xiaoquan-Xinchang area.Modeling results show that structural fractures are poorly developed in this area,except in the near-fault regions where regional structural fractures are relatively well developed. Seismic section interpretation and structural evolution analysis reveal that the main fractured zones are good hydrocarbon migration pathways and no serious leakage of hydrocarbons exists.Therefore,favorable regions for gas exploration are those neighboring faults,especially the near E-W trending faults which are parallel with the current major stress and in open state can more effectively conduct gas.

An analysis of main control factors and accumulation patterns of gas reservoirs in Lower Cretaceous in southern Songliao basin

He Xinghua

2004, 25(1):  75-80.  doi:10.11743/ogg20040114

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This paper discusses the essential petroleum geological conditions of gas accumulations in the Lower Cretaceous in Southern Songliao basin based on the achievements got in exploration and development in recent years. Source rocks are lacustrine dark mudstone and coal measure strata,reservoir rocks are mainly sandbodies of subaqueous fan delta and delta facies,and local and interlayer cap rocks constitute effective seals of gas accumulations in the Lower Cretaceous. Vertically, there exist three reservoir combinations(lower, middle and upper),of which the middle and upper reservoir combinations are the result of modification and remigration of hydrocarbons in the lower combination. Hydrocarbon source, structure, trap and preservation conditions are the main factors controlling gas accumulation in the Lower Cretaceous. Laterally,gas accumulations in the Lower Cretaceous are separately distributed in fault depressions and become several gas-bearing units.Hydrocarbons in the fault depressions are characterized by their annular distribution,i.e. gas zone, oil & gas zone and oil rim are successively distributed from the center of fault depression to the swell at the boundary.Gas are enriched vertically in three horizons, i.e. Nong'an gas horizon in lower Quantou Formation, Xiaochengzi gas horizon in Denglouku Formation and Wujiazi gas horizon in Yingcheng Formation. All of them are characterized by cross-over and multistage accumulations.

Reservoir dynamic monitoring: a commentary on time-lapse (or 4-D) seismics

Cui Yongqian, Liu Chiyang, Zhang Yiming

2004, 25(1):  81-87.  doi:10.11743/ogg20040115

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Time-lapse seismic (4D seismic) technology, a reservoir dynamic monitoring technology rapidly developed in recent years, has become a new tool for reservoir management,and has widely been applied in many oilfields,especially offshore oilfields. The application of this technology is continuously enlarging and the accuracy is continuously increasing with the deepening of study on petrophysical properties and the development of relevant technologies. Currently, time-lapse seismic technology is used to monitor changes of oil recovery, oil displacement efficiency and fluid front, to identify areas with bypassed oil, as well as to monitor sealing capacity or leakage of faults. The key to seismic acquisition is to improve repeatability and signal-to-noise ratio. New technologies,such as cross equalization, normalization and bin parameter recombination and the principle of synchronous processing of new and old data,are applied so as to ensure that the final seismic differences are the only results of fluid flow changes in reservoirs. Based on direct interpretation, reversion and property analysis, seismic history match and dynamic reservoir description are developed as seismic interpretation technologies and are used in combination with other subjects and technologies to reduce non-uniqueness of interpretation. Remarkable progresses have also been made in respect of lowering investment risk of projects and feasibility study. The application conditions and limitations of the technology should be considered when carrying out time-lapse seismic projects. With the deepening of research on time-lapse seismic techniques and enriching of experiences, time-lapse seismic reservoir monitoring will progress more rapidly and will more widely be applied.

Automatic tracing of reservoir's sedimentary microfacies

Xue Linfu, Wang Jian, Wang Dongpo, Mei Qitai, Sun Quan

2004, 25(1):  88-92.  doi:10.11743/ogg20040116

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Automatic tracing of reservoir's sedimentary microfacies is to predict automatically the distribution and boundaries of sedimentary microfacies and draw facies map by using computer technologies based on interwell stratigraphic classification and correlation and analysis of sedimentary microfacies. It is carried out in 5 steps including coordinate transform of well positions, gridding, interpolation, superposition, search of boundaries and drawing sedimentary microfacies map. The key of this method is to determine the distributions of different sedimentary microfacies by spatial interpolation and "worm" interpolation,and create a map of sedimentary microfacies belts through superposing these microfacies distributions."Worm"interpolation, unlike conventional interpolation methods, is an intelligent method that mimic human to analyze zonal distribution of sedimentary microfacies based on geologic rules. The MFBTS (Micro-Facies Belt Tracing System)software, developed according to the above mentioned principles, provides a tool for analyzing and tracing rapidly the distribution of reservoirs and sedimentary microfacies. Application of this technique in Putaohua oilfield in Songliao Bsasin shows that the map of sedimentary microfacies created by MFBTS is basically consistent with that drawn by hands.

Seismic response and frequency difference analysis of cavern-type reservoirs in carbonates in Tahe oilfield

Wang Zheshun, Wang Shangxu, Tang Wenbang

2004, 25(1):  93-96,101.  doi:10.11743/ogg20040117

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Systematic study of composite reflectance coefficient of solution cavity shows that the seismic response is characterized by strong amplitude, low velocity and harmonization. This paper discusses the conditions of occurrence of strong reflectance and the reflectance signatures of cavities with different filling materials, and believes that strong reflectance waves can be observed in seismic data with normal frequency (20～30 Hz). According to the relationship between height of cavity,property of filling material and signal frequency, a frequency difference prediction and analysis technology is developed on the basis of wave equation. Its application in Tahe oilfield shows that this technology can get amplitude-frequency and velocity-frequency anomalies in cavities filled with fluid at a burial depth of over 5000 m, with over 100 m width and over 3 m height from normal seismic data with predominant frequency of 20～ 30 Hz. The anomalies appear in different zones and different layers with vertical and lateral comunications. They can be used as the basis for determining the existence of cavities, their distribution and estimating their heights.

Scale control through water mixing in waterflooding oilfields

Pan Aifang, Q? Zhihao, Ma Runyong

2004, 25(1):  97-101.  doi:10.11743/ogg20040118

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Scale control through water mixing is an economically applicable, simple, highly effective and pollution free technology. Injection water is mixed with formation water or produced water in optimum proportion at surface. Ca(OH) 2solution is used to control pH value. All the cations, such as Ba²⁺, Ca²⁺, Fe³⁺, Fe²⁺ and Sr²⁺ and anions,such as OH^-, CO₃^2-, HCO₃^-, SO₄^2- and S^2- will be precipitated from the solution through reaction when the pH value in the mixed water is above 8.35. On the one hand,the scale-forming ions are removed and scaling is prevented when formation water mix with injection water in oil reservoir, so as to protect the oil reservoir. On the other hand,iron would be in a passivation state of corrosion,and water pipeline would be prevented from scaling and rusting.Experimental studies show that this technology can not only control scaling and damaging of oil reservoir and scaling and rusting of water pipeline, so as to realize reutilization of produced water and to reduce production cost, but is also applicable for waterflooding in various oilfields.

Application of pattern recognition in stratigraphic division

Chen Qinghua, Zhang Fengqi, Sun Shupeng, Liu Chiyang

2004, 25(1):  102-105,114.  doi:10.11743/ogg20040119

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Pattern recognition is to subsume undetermined patterns with computer technologies based on study and classification of the known patterns.Pattern recognition can be performed in three steps.First,preprocess data through Fourier analysis,regression analysis and multi-point smoothing;then calculate frequency spectrum of the known wells' geological data by using cyclical strategraphy and perform feature study and extraction and pattern classification with Milankovitch cyclic components;and finally classify strata in other wells by using the established patterns.Strategraphic division has been performed in 40 wells in Dagang oilfield with the pattern recognition method and the results are in good agreement with the original ones and have better accuracy.

Study of Paleozoic sequence stratigraphy in Jiyang depression

Li Mingjuan, Zhang Hongnian, Hu Zongquan, Zhang Fushun

2004, 25(1):  106-110.  doi:10.11743/ogg20040120

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The Paleozoic in Jiyang depression can be divided into three super-sequences and 14 third-order sequences by using sequence stratigraphy theory and cycle analysis of datum level,combining with drilling, seismic and logging methods. The super-sequences are the Mantou formation-Liangjiashan formation (A), the Xiamajiagou formation-Badou formation (B) and the Benxi formation-Shiqianfeng formation (C). According to calibration of sequences in regional seismic profiles, an isochronic framework of the Paleozoic sequence stratigraphy in Jiyang depression is established through tracing and interpreting the four super-sequence boundaries. The three super-sequences are clear in logging-constrained inverse profiles, showing low, high and low impedances from bottom to top,respectively. The main identification marks of sequence boundaries are unconformable surfaces, scouring surfaces of rivers, surfaces showing abrupt changes of litho-electric properties and color, of which unconformable surfaces are super-sequence boundaries, while others are boundaries of third-order sequences. Standards for dividing seismic sequences are defined and a sedimentation model is developed for the Paleozoic sequence stratigraphy in Jiyang depression

Prediction of conductivity of hydraulic fracturing induced fractures with gray models

Yang Y?, Sun Zhixue, Guo Chunhua

2004, 25(1):  111-114.  doi:10.11743/ogg20040121

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Fracture conductivity directly influences productivity of fractured formation and is an important index for evaluation of fracturing. This paper analyzes the prerequisites and methods to calculate conductivity of hydraulic fractures through transient test. Taking Xinchang gasfield in Sichuan basin as an example,using partial correlation method,formation and operational parameters that influence conductivity of hydraulic fractures including formation thickness,interval transit time, shale content, proppant content, pump output and preflush volume are optimized.GM(1,h) gray model is introduced to increase the accuracy of conductivity prediction.This method can also be used to predict fracture half-length and production gain factor. The prediction accuracy of production gain factor, however, is poor due to the influences of unpredictable factors such as skin.Therefore fracture conductivity is relatively suitable for evaluation of fracturing effects.

Reservoir characteristics of deep volcanic rocks and prediction of favorable areas in Xujiaweizi fault depression in Songliao basin

Liu Weifu

2004, 25(1):  115-119.  doi:10.11743/ogg20040122

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Volcanic rocks in Xujiaweizi fault depression in Songliao basin can be classified into lava and vocaniclastic rocks.The effective reservoir spaces of volcanic reservoirs are pores and fissures. Fissures can not only act as reservoir spaces, but can also interconnect pores of different types and promote dissolution at later stages. A computation model of fissure porosity is developed based on recognition of fissure types. According to logging interpretation of 12wells, the volcanic reservoirs are divided into 3 grades based on their fracture porosity,i.e.grade Ⅰ with porosity above 0.5%, grade Ⅱwith porosity ranging from 0.2% to 0.5%, and grade Ⅲ with porosity below 0.2%. Volcanic rock facies can be subdivided into marginal, transitional and central subfacies. The central subfacies, located near volcanic conduit, has well developed structural and contraction fissures and relatively good poroperm characteristics,so it would be the most favorable reservoir facies belt; the transitional subfacies, having relatively well developed fissures and moderate poroperm characteristics,would be a favorable reservoir facies belt; while the marginal subfacies has poor poroperm characteristics,it would be an unfavorable reservoir facies belt.