Journal of Earth Science, Vol. 25, No. 2, p , April 2014 ISSN X Printed in China DOI: /s

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1 Journal of Earth Science, Vol. 25, No. 2, p , April 2014 ISSN X Printed in China DOI: /s Fine Stratigraphic Division of Volcanic Reservoir by Uniting of Well Data and Seismic Data Taking Volcanic Reservoir of Member One of Yingcheng Formation in Xudong Area of Songliao Basin for an Example Huanqing Chen, Yongle Hu, Jiuqiang Jin, Qiquan Ran, Lin Yan Research Institute of Petroleum Exploration and Development, PetroChina, Beijing , China ABSTRACT: Taking member one of Yingcheng Formation of Cretaceous in Xudong area, Xushen Gas Field of Songliao Basin for an example and aimed at the diachronous problem generally existed in volcanic reservoir division, firstly advanced the method of two steps and two unites in the researches of volcanic reservoir finely division that guided by the method that sources controlled and founded the stratigraphic trellis. In this process, volcanic edifices and bodies were identified and traced. The results indicated that aimed strata in study areas could be carved up to six layers of YC1I1, YC1I2, YC1I-II, YC1II1, YC1II2 and YC1III from the top to the bottom. Analyzing causes and firmly united of well data and seismic data could achieve fine stratigraphic division of volcanic reservoir. Surfaces of layers and volcanic bodies were basically unanimous in side direction. Stratum inclination gradually reduced with the distances increased from craters. The results of volcanic reservoir division had preferable consistency with lithologies and volcanic lithofacies and dynamic development data. The researches offered a useful method to stratigraphic division of volcanic reservoir and it had very important significance to effective development of volcanic reservoir in practice. KEY WORDS:stratigraphic division and correlation of volcanic stratum, volcanic body, volcanic reservoir, Yingcheng Formation, Xushen Gas Field. 1 INTRODUCTION Stratigraphic division and founded of stratified database always is one of the most basic and critical tasks. Taking clastic for an example, accurate stratigraphic division could not only found isochronous stratigraphic framework and offer foundations to the latter investigations, but also is favorable to forecast sedimentary sandstones developed in different system tracts or different positions of sequences in hydrocarbon exploration. To researches of petroleum development, it has very important significance to reservoir modeling and accumulation description and oilfield effective exploitation in practice (Chen and Zhu, 2008; Guo et al., 2001). Fine stratigraphic division also has the same magnitude meaning to volcanic reservoir researches. Nowadays, the facts that followed the understanding of methods used in clastic stratigraphic division generally existed in volcanic reservoir study. These actualities always led to the diachronous contradiction of stratigraphic division through volcanic bodies. Aimed at this problem, the article takes volcanic reservoir of member one of Yingcheng Formation of *Corresponding author: hqchen.1999@yahoo.com.cn China University of Geosciences and Springer-Verlag Berlin Heidelberg 2014 Manuscript received January 29, Manuscript accepted April 25, Cretaceous in Xudong area in Xushen Gas Field of Songliao Basin for an example, explored the matter of fine stratigraphic division of volcanic reservoir, which guided by the ideology of source controlled theory. A suit of applied research thoughts and techniques about fine stratigraphic division of volcanic reservoir were summarized. 2 GEOLOGICAL SETTINGS Xushen Gas Field lies in Daqing-Anda area in Heilongjiang Province. It was located in Xujiaweizi faulted in the northern of Songliao Basin in regional tectonic. The faulted formed up during geological period of latter Jurassic to Early Cretaceous. The strata is divided to Huoshiling Formation and Shahezi Formation and Yingcheng Formation and Denglouku Formation and the member one and member two of Quantou Formation from the bottom to the top. Because of frequent volcanic movement, there developed a mass of volcanic productions in Yingcheng Formation. The volcanic reservoirs are mainly developed in the member one and member three of Yingcheng Formation of the lower series of Cretaceous, and acid eruption rock takes dominion roles. Nowadays, Xushen Gas Field has thousands of gas reserves and 89.8% of them come from volcanic reservoir, and they are the leading field of natural gas development in Daqing Olifield (Shu et al., 2007; Huang et al., 2006; Xu et al., 2006; Wu et al., 2002). The study area of Xudong area lies in the middle part of Xujiaweizi Chen, H. Q., Hu, Y. L., Jin, J. Q., et al., Fine Stratigraphic Division of Volcanic Reservoir by Uniting of Well Data and Seismic Data Taking Volcanic Reservoir of Member One of Yingcheng Formation in Xudong Area of Songliao Basin for an Example. Journal of Earth Science, 25(2): , doi: /s

2 338 Huanqing Chen, Yongle Hu, Jiuqiang Jin, Qiquan Ran and Lin Yan Strata Series For ma - tions Upper Jurassic Lower Cretaceous Shahejie Formation Yingcheng Formation Denglouku Formation Huoshiling Formation Segments Member two Member one Member four Member three Member two Member one Upper member Lower member Member two Member one Lithology Nenjiang River Western slope region Qiqihaer Duerbote Da an Fuyu Lindian Nenjiang Nehe River Yi an fault depression Changjiaweizi fault depression Gulong fault depression Daqing step fault zone Western fault depression region Anda-Zhaozhou anticline zone Lindian fatlt depression Central fault-uplift region Daqing Northern slope region Anda Xujiaweizi fault depressed zone Zhaozhou Keshan salient Mingshui slope Zhaodong-chaoyanggou anticline zone Keshan Mingshui Southeastern fault depression region Songhuajiang River Bei an Bei an fault depression Northeastern fault-uplift region Hailun salient Suihua fault depressed zone Lanxi salient Suihua Yingshan fault depressed zone Haerbin Southeastern fault-uplift region N Base- ment Tuff Andesite Andesitic breccia Conglomerate Pebbled sandstone Sandstone Mudstone Thin coal bed Study area Figure 1. Sketch map of strata and structure divided of Xushen Gas Field in Songliao Basin (after Wang and Xi, 2009). faulted, and it has been the most important gas target area in Xushen Gas Field at present. The aimed strata in the article is member one of Yingcheng Formation of the lower series of Cretaceous (Fig. 1) (Wang and Xi, 2009). 3 THOUGHTS OF STRATIGRAPHIC DIVISION AND CORRELATION OF VOLCANIC RESERVOIR Because of the volcanic eruption action represents characteristics that polycyclic controlled by craters, stratigraphic division and correlation of volcanic stratum compares quite different with clastic. The previous did lots of works about researches of stratigraphic division and correlation of volcanic reservoir (Zhang, 2009; Stewart and Davies, 2006; Chen and Li, 2004; Zeng et al., 1996). Zeng et al. (1996) analyzed the problem of stratigraphic division of volcanic reservoir of Paleogene in Chunxi area in Dongying depression, the rules of rock layer boundaries and volcanic actions with sedimentary cycles and volcanic rock with ages of surrounding rock which should be mostly considered in practices were pointed out. Chen and Davies (2004) compartmentalized the volcanic reservoir of Permian in the middle of Tarim Basin. Stewart and Davies (2006) analyzed the structure and extension characteristics of mudstone volcanic systems in southern Caspian Basin by using three-dimensional seismic data, and its influence to reservoir properties was evaluated too. Zhang (2009) discussed stratigraphic division and correlation of volcanic reservoir of Jurassic to Cretaceous in Jiangsu Province. The method by using the sedimentary stratum which on or under or inside the volcanic stratum to limited volcanic reservoir boundaries were emphasized in the predecessors s researches, but fine stratigraphic

3 Fine Stratigraphic Division of Volcanic Reservoir by Uniting of Well Data and Seismic Data 339 isochronous division and correlation inside the volcanic stratum rarely involved. To Yingcheng Formation in Xushen Gas Field, previous mainly carved up it to member one and member two and member three and member four (Hou et al., 2009; Pang et al., 2009; Xu et al., 2006), and fine stratigraphic isochronous division and correlation haven t be seen until nowadays. The well data and seismic data were firmly united, and fine isochronous division and correlation of volcanic reservoir of the member one of Yingcheng Formation in Xudong area in Songliao Basin were achieved principium. The results of stratigraphic isochronous division and correlation were validated by the lithologies and lithofacies and oilfield dynamic data. The diachronous contradiction of hierarchical circumscriptions through volcanic bodies was resolved. On the base researches did above on, a suit of applied research thoughts and techniques about volcanic reservoir fine isochronous division and correlation were trying summarized. Aimed at the precision requests and based on the understanding of crater and volcanic eruption intensity controlled the development scales of volcanic bodies and distribution characteristics of volcanic stratum (elements of landform and conformation should be calculated too), the method of two steps and two unites of fine isochronous division and correlation of volcanic reservoir were firstly brought forward. So-called two steps, the first step is the founded of large scale of isochronous stratigraphic framework. And the second step is subdivision layers inside of it. Two unites were uniting of well data with seismic data in data aspects and the linked of volcanic eruptions cycles with volcanic bodies (or volcanic edifices) in thoughts and adequately incarnates genetic mechanism. The large scale of isochronous stratigraphic framework was founded after defined of conformation elements and volcanic lithologies and volcanic eruption mode. The data of cores description and thin sections identification and analysis and testing and well logging and seismic reflection characteristics were closely united and the geological settings and basin development history were consulted. According to cognitions of volcanic eruption cycles controlled the distributing of volcanic bodies in space, the top or bottom boundaries of different volcanic bodies of different craters during the same volcanic eruption periods were linked on and traced and closed in space. In the process, volcanic edifices and bodies were identified at firstly by using the survey lines network. Finally, database of stratigraphic division and correlation of volcanic reservoir has been founded. 4 FINE ISOCHRONOUS DIVISION AND CORRELA- TION OF VOLCANIC RESERVOIR 4.1 Volcanic Eruption Mode Controlled Stratum Distributing Profound understanding of volcanic eruption mode could deepen cognitions of distributing laws of volcanic reservoir in space. Previous did lots of works about volcanic eruption mode of Yingcheng Formation in Xudong area in Xushen Gas Field. Xu et al. (2006) did some researches about space-time collocated relationship between volcanic rock development and local rupture evolvement, and the viewpoint that volcanic eruption mode mainly were eruption of central type in Xushen Gas Field was been pointed out. Yan et al. (2008) studied volcanic characteristics and volcanic eruption mode of member one of Yingcheng Formation in Xingcheng area in Xujiaweizi faulted in Songliao Basin. In this process, the data of cores and thin sections identification and geochemical analysis of whole core and well logging and seismic reflection were used. Consulted productions of predecessors, the article indicated that the volcanic eruption mode of member one of Yingcheng Formation in Xudong area in Xushen Gas Field was cranny-central type. Big ruptures controlled craters distributing. The results of volcanic lithofacies showed that crater and volcanic eruption intensity controlled the distributing of volcanic reservoir. The paleotopography and conformation evolvement characteristics had some effects to volcanic reservoir extended (Fig. 2). Generally speaking, the volcanic stratum mainly represented mound characteristics which neared the craters while it behaved samdwich characteristics far away from the crater (Fig. 2). The things are very distinctness (Fig. 3). 4.2 Foundation of the Large Scale of Isochronous Stratigraphic Framework The large scale of isochronous stratigraphic framework Volcanic breccia Breccia tuff Tuffaceous siltstone Siltstone Sandy mudstone Sedimentary tuff Breccia lava Mudstone Volcanic conduit Extrusive facies Breccia tuffaceous lava Rhyolite Explosive facies Overflow facies Volcanogenic sedimentary facies Figure 2. Mode map of volcanic eruption characteristics in Xudong area in Xushen Gas Field.

4 340 Huanqing Chen, Yongle Hu, Jiuqiang Jin, Qiquan Ran and Lin Yan Figure 3. Characteristics of seismic reflection of volcanic reservoir of member one of Yingcheng Formation in Xushen Gas Field; the blue line were boundaries of different volcanic edifices, and the definition and correlation researches contents would be detailedly discussed in the latter part. corresponded member one of Yingcheng Formation in the researches. In this stage, the methods and rules were similarity with sedimentary rock. So the methods used in clastic rock could be consulted at this time and the theory of sequence stratigraphy could be fetched in (Chen et al., 2009). Territorial key horizon and boundaries could be found at first that could be confirmed by the sedimentary stratum formed in the volcanic eruption intermission and regional unconformity surfaces. In the process, seismic data took the dominant role while well data and geological data took the assistant roles. The top interface and bottom interface both have characteristics representation in well logging and seismic section (Figs. 3 and 4). Yingcheng Foramtion could be divided to four segments of member four and member three and member two and member one from the top to the bottom in Xushen Gas Field. Member two and member three were absented in Xudong area in Xushen Gas Field. Sandstone-mudstone sediments developed in the lower part of member four, and the acid volcanic mainly developed in member one. Angle surface of unconformity engendered between the double layers which could be traced from seismic sections easily. The bottom of member four of Yingcheng Formation is mudstone layer which behaved a suit of high number of GR and lower number of RT. Volcanic rock of member one represented high number of GR and RT. The top layer of Shahezi Formation is sandstone-mudstone with lower number of GR and RT. The boundary of it with member one is evidence. The boundaries of stratum behaved crust of weathering and sedimentary interlayer in the data of cores and outcrops. After repeatedly contrasted, the boundaries of member one of Yingcheng Formation were confirmed through tracking and closing these seismic boundaries. The 3-D isochronous stratigraphic framework of Lingshui Formation was established lastly. Then the jobs of volcanic edifices or volcanic bodies tracing could be done. 4.3 Identified and Traced of Volcanic Edifices and Volcanic Bodies Volcanic edifices are accumulations formed by volcanic clastic and lava which erupted during a period of times and surrounded volcanic conduits (Wang and Zhou, 1982). The article defined the geological ages of volcanic edifices from 136 to 128 Ma, and it is almost corresponding to member one of Yingcheng Formation. Because of volcanic eruption cycles controlled the distributing of volcanic bodies in space and craters played a governed role in volcanic edifices developed, one or linked by one large rupture a suit of craters corresponded one edifice (Figs. 3 and 5). All these volcanic edifices touched each other and formed volcanic stratum of member one of Yingcheng Formation in Xudong area in Xushen Gas Field. The recognizing of volcanic edifices and bodies should surround of identifying of craters and volcanic conduits firmly. In particular, volcanic edifices were corresponded to craters one by one in generally. Craters are eruption channels of volcanic lava. Volcanic eruption productions deposited nearby and encircled craters by gravity action and mainly formed geomorphological characteristics of uplift. Volcanic conduit lies below the crater, they often behaved erection rhyolite structure and explosive breccia and breccia lava and columnar joints in large scale because of nearly vertical flow of fused slurry and effects of exploded gas-liquid. Craters and volcanic conduit have characteristics of exhaled direction top and unorganized and occurrences nearly vertical in seismic reflections. They are micro structure in forward direction on structural map and disorder characteristics in coherence cube analyzed and nearly represented rotundity. It behaved high obliquity number and distributed annularity or hoof figure. By using method of seismic section analyzing and micro-structure analyzing and seismic attributes analyzing, craters and volcanic conduit could be effectively recognized. Volcanic bodies developed inside volcanic edifices and they corresponded a short geological age, and one edifice could comprised by several volcanic bodies.

5 Fine Stratigraphic Division of Volcanic Reservoir by Uniting of Well Data and Seismic Data 341 Figure 4. Stratum trellis of stratigraphic division of Yingcheng Formation in Xudong area in Xushen Gas Field. Tomohisa et al. (2000) did some researches about volcanic bodies recognizing and tracing when they carved up volcanic reservoir. All these were parts of their researches about geological modeling of heterogeneity volcanic reservoir by using lithology methods. Prospective precision could be got only when the seismic data and well data adequately united in the process of volcanic bodies recognizing and tracing. The well data play leading role. In a sense, recognizing and tracing volcanic bodies were similarity with it did about volcanic edifices. The only different thing is that the scale of the former is more subtle than the latter. The boundaries of volcanic edifices and bodies are strong reflection events and entirely changes of different reflection wave groups and occurrence broken and continuous reflection wave groups interrupted abruptly and other characteristics. It is number saltation in well logging and lithology mutation in logging or structure changes in the same lithology. It s characteristics in cores are similarity with logging. It behaves mutation of physical properties of porosity and permeability. Because of the volcanic actions destroyed volcanic edifices or volcanic bodies formed by the former volcanic eruption, different edifices or volcanic bodies with the same lithologies maybe touched directly. Then the imperceptibility changes of seismic reflection events and well logging lines should be noticed. 4.4 Fine Stratigraphic Division and Correlation of Volcanic Reservoir inside Isochronous Stratigraphic Framework Founded large scale of isochronous stratigraphic framework and accomplished identified and traced of volcanic edifices and bodies inside this framework, the jobs of stratigraphic division and correlation of volcanic reservoir could be done. In this process, the data of seismic reflection and well logging and cores description and even geochemical analysis of whole core should be used coalescent. On the seismic sections, strong events and changes characteristics of neighbor seismic reflection groups and breaking touched relationship of different seismic reflection groups (Fig. 6a). The works resembled with volcanic bodies recognizing. The former is more refined than the latter. The boundaries of finely stratigraphic division and correlation of volcanic reservoir have lots of characters in well data. Such as, the number chopped in well logging, lithology waved in logging, changes of lithology and rock structure in cores, lithology and micro rock structure variety in different depths and so on. Of course, all kinds of analysis and test data also are the key to this task. All changes about lithology and rock composition and flow properties in lithology offered by data mentioned above could afford powerful evidences to layers boundaries true identified. The things worthy to be talk about is that it should make right choice when these data and methods have some conflicts in practice. If the seismic data disagree with well data, the latter should be chosen. After synthetically analyzed multi-data above on, the top or bottom boundaries of different volcanic bodies of the different craters during the same volcanic eruption periods were linked on and traced and closed in space. Then database of stratigraphic division and correlation of volcanic reservoir of member one of Yingcheng Formation in Xudong area in Xushen Gas Field was been founded. Authors thought that the boundaries of layers fine stratigraphic division and correlation may through different volcanic edifices and compartmentalize stratum cell which shorter than member and formed inside different volcanic edifices in the same stages. The boundaries of layers fine stratigraphic division and correlation shouldn t through volcanic bodies because of one volcanic body formed in a correspondingly isochronous ages. A suit of isochronous stratum cell could contain lots of volcanic bodies, and these volcanic bodies could belong to one volcanic edifice or different volcanic edifices. This time the volcanic stratum of member one of Yingcheng Formation in Xudong area in Xushen Gas Field was carved up to six layers of YC1I1 and YC1I2 and YC1I-II and YC1II1 and YC1II2 and YC1III from the top to the bottom (Fig. 6b). Demanding to explain, the section didn t cross the center location of crater

6 342 Huanqing Chen, Yongle Hu, Jiuqiang Jin, Qiquan Ran and Lin Yan Figure 5. Characteristics of volcanic distinguished by uniting well data and seismic data, different color areas represented different volcanic edifice. and crater (At areas of XS21-5 and XS21 and XS21-2) hillock characteristics behave not obvious in section plane. The crater only represented a part of flank. Volcanic bodies have nearly relationship with volcanic lithfacies because of different volcanic lithofacies developed in specific positions. Study on the development characteristics of volcanic bodies and volcanic lithfacies of aimed layers in study area (Fig. 6b), and overflow facies were comparted by explosive facies and extrusive facies developed nearby volcanic conduit and volcanogenic sedimentary facies mainly distributed in intermission of volcanic eruption cycles whose regularity of developed locations aren t evidence. The intensity of volcanic eruption controlled the scale of volcanic bodies. It controlled the development characteristics of volcanic lithofacies and sub-lithofacies with elements in space and led to difference between volcanic lithofacies of every layer. Contrasted the method of stratigraphic division and correlation this time with the stratiform method of stratum compartmentalized widely used nowadays (Fig. 6b), the former adequately considered the cause of formation mechanism in the process of stratigraphic division and correlation. The boundaries of stratum compartmentalized are consistent with volcanic bodies formed in different geological ages. The stratum mainly represented hillock characteristics nearby the crater as well as stratiform character far away from the crater (Fig. 6b). The mistakes of using method about clastic rock in volcanic stratum compartmentalized are very distinctness. The boundaries of layers cross the different volcanic bodies time after time and conflicts of diachroneity are quite extruded. The boundaries of layers are not isochronous ranges (Fig. 6c). These also proved that the methods of two steps used this time were exactness. 4.5 Results Validated of Stratigraphic Division and Correlation of Volcanic Reservoir The database of volcanic reservoir found these times were been tested at last. The targets mainly achieved by checking of volcanic lithology and volcanic lithofacies and production dynamic data of volcanic reservoir in different stratum cells. After testing, the results of stratigraphic division and correlation of volcanic reservoir these times were reality and credibility, and they could be used in production practice. The types of volcanic rock included two kinds of volcanic lava and pyroclastic rocks and ten species in further. The rhyolite and rhyolite tuff and sedimentary volcanic breccia were mainly developed. Characteristics of these lithologies were distinctly in cores and slices (Fig. 7) and they developed inside different stratum cells. Cores analyzing results indicated that volcanic eruption intensity and characteristic had diversity in different volcanic eruption periods and stages. Different layers corresponded characteristics lithologies in different volcanic eruption periods and stages (Table 1, Fig. 8). Upper and lower the boundaries of volcanic reservoir in this times, lithologies often change in generally (Table 1). Of course, the stratum with same lithologies of different volcanic bodies formed in different stages may touch directly because of the destroyed of volcanic bodies that younger ones to older ones and older ones lost some parts. The delamination boundaries may lie in the same lithology. Certainly, this status is not diachroneity conflicts Volcanic lithofacies characteristics in different stratum cells Different volcanic eruption cycles developed inside different volcanic bodies (or volcanic edifices). They were overly in longitudinal while interleaving in lateral. To a whole volcanic eruption cycle, the volcanic lithofacies which formed during the early stages were different with the middle ones or the latter ones. In a general way, volcanic lithofacies may change nearby the subtly hierarchical boundaries of stratum. The circumscriptions of volcanic lithofacies likely coincide with boundaries of layers (Table 1, Figs. 6a and 8), so the

7 Fine Stratigraphic Division of Volcanic Reservoir by Uniting of Well Data and Seismic Data 343 Figure 6. Results of volcanic reservoir carved up of member one of Yingcheng Formation in Xudong area in Xushen Gas Field. (a) seismic section of member one; (b) volcanic stratum and lithfacies; (c) clastic rock of volcanic stratum and lithfacies.

8 344 Huanqing Chen, Yongle Hu, Jiuqiang Jin, Qiquan Ran and Lin Yan former sometimes may use to test the latter. Because of absented of volcanic bodies, volcanic lithofacies belonged to different volcanic bodies touched directly, then the volcanic lithofacies may change abruptly or the same volcanic lithofacies formed in different geological stages may contact straightly in space. These circumstances should be careful. Figure 7. Characteristics of core and microscope photos of Volcanic rock of member one of Yingcheng Formation in Xudong area in Xushen Gas Field. (a) Pore rhyolite, Well-XS23, depth m; (b) angular pebbles lava, Well-XS21-1, depth m; (c) tuff chipping crystal, Well-XS42, depth m, 5 10; (d) volcanic breccia, Well-XS24, depth m, Production dynamic characteristics of different stratum cells Interrelated geological data of gas pool are used to test the results of stratigraphic division and correlation of volcanic reservoir. Near gas pool section whose direction from south to north which drew with united data of perforation and gas testing and production test and gas-water layers interpretation with well logging was chosen to accomplish the task. Different volcanic bodies of different isochronous layers composed different gas-water systems. And the same layer is a gas-water system. Take Well1 as an example, the stratum of it could be divided to six layers from the top to bottom. The gas layer is on the top Figure 8. Map of relationship between divided results of stratigraphy and volcanic lithology with volcanic lithofacies. while the water layer is under it inside every layer. The same things happened to Well 2 and Well 3. So the production dynamic data are finely according to results of isochronous stratigraphic division and correlation. Nowadays, these results of stratigraphic division and correlation have been used in the exploitation project of volcanic reservoir of member one of Yingcheng Formation in Xudong area in Xushen Gas Field of Songliao Basin. The adjusted of old wells and the new horizontal wells that based on database of stratigraphic division and correlation these times have achieved the prospective purpose. The method adapted to volcanic reservoir with well data and seismic data which in the early stages of oilfield development. To volcanic reservoir in the stages of development life that with plenty data, the effects would be better because of the increasing of information. The method discussed in the paper would have important consulted value to stratigraphic division and correlation of Yingcheng Formation in Xushen Gas Field and other areas and even the whole Songliao Basin. 5 CONCLUSION (1) The method of two steps and two unites in researches of fine stratigraphic division and correlation of volcanic reservoir is adapt to reservoir characteristics that controlled by volcanic eruption cycle and volcanic eruption intensity. It could resolve conflicts of diachroneity and achieve fine isochronous division and correlation of volcanic reservoir which offered steady foundations to volcanic reservoir effective development. The method is the same with the oil field from the early development stages to the development life, and it has widely applications foreground.

9 Fine Stratigraphic Division of Volcanic Reservoir by Uniting of Well Data and Seismic Data 345 Table 1 Characteristics table of volcanic lithofacies and volcanic lithology of Yingcheng Formation in Xushen Gas Field (after Wang et al., 2008; Shu et al., 2007) Facies Subfacies Genetic mechanism and division symbol Types of lithology Structure Volcanic conduit (located in the lower of the volcanic bodies) Extrusive facies (most formed in the early stage and later stage of volcanic eruption cycles) Explosive facies (most formed in the early stage of volcanic eruption cycles) Overflow facies (most formed in the middle stage of the volcanic eruption cycles) Volcanogenic sedimentary facies (formed in any stage of the volcanic eruption cycles) Volcanic neck Rock melt flowed stagnation and filled volcanic channels, slumped filler of crater Being transition types of pyroclastic rock and lava, Porphyritic construction fusion sintering structure Secondary volcanic Formed by magma invaded in surrounding rock and condensated slowly mainly being fusion bonded breccia lava and breccia breccia tuff texture hydrothermal breccia Formed by the underground explosion effect lava, also could see breccia produced by the pressure reliefed partly crystal fragments tuff during magma rich in volatile invaded in the rocks fracture zone Inner extrusive High viscosity fused slurry extruded by Auto crushing and breccia Fusion sintering breccia and internal force and flowing and packing nearby lava and lava fusion bonded tuff texture, Middle extrusive crater, formed dome or deformed and glassy texture and pearlitic texture, sub-facies shovel-scrape and encapsulated newborn and Outer extrusive antephase rock block and flowing by internal Less phenocryst texture, crushing force extrusion phenocryst texture Splash down Rock block nearby crater formed by the rock Breccia lava and tuff lava Fusion sintering breccia tuff melt carringing surrounding rock and rock melt and fusion bonded breccia texture itself falling down Pyroclastic flow Torrid clastic materials pushed by the follow-up Rhyolitic crystal fragments Fusion sintering tuff texture, ejecta and the own gravity and flowed fusion bonded tuff domi- volcanic clastic texture along surface after gas launched collapsed, and nated rock types mainly were fusion bonded tuff that containing crystal fragments and glassiness clastic and magma clastic and cutting Thermal basal wave Gas-phase and solid and liquid turbidite system Rhyolitic crystal fragments Pyroclastic structure (crystal that formed by gas launched effect carried by tuff dominated fragments tuff texture gravity nearby surface and showed suspended dominated) load, and steam flow carried clastic. Main was tuff containing crystal fragments and glassiness clastic and magma clastic. Air falling Solid and plastic ejecta free fall moving of gas Volcanic breccia and Agglomeration structure, launched and effected by wind. crystal fragments or cutting breccia structure, agglomerate which containing volcanic bombs tuff and rhyolitic breccia tuff texture and floating rock block and breccia and crystal crystal fragments tuff and fragments tuff rhyolitic crystal fragments tuff dominated Top overflow Rock melt containing crystallization Stomatal rhyolite, basalt and Spherulitic texture, precipitated matter and syngenetic breccia dacite fine crystalline structure pushed by follow-up ejecta and own gravity Upper overflow and flowed along surface. primary pores developed in upper and fractures formed by Middle overflow structure developed in lower, and primary Basalt, rhyolite and dacite Fine crystalline structure, pores and fractures formed by structure existed porphyritic texture Lower overflow in middle but not developed Fine crystalline rhyolite, Glassy texture, basalt and dacite fine crystalline structure, porphyritic texture, breccia structure Reworked volcanogenic Volcanic clastic reformed by flow effects All kinds of volcanic Terrigenous classic structure sediments breccia and tuff Volcanogenic Volcanic clastic dominated and maybe some All kinds of volcanic rocks Terrigenous classic structure sedimentary facies other terrigenous clastic added and sedimentary rocks hybrid

10 346 Huanqing Chen, Yongle Hu, Jiuqiang Jin, Qiquan Ran and Lin Yan Figure 9. Gas reservoir section of Well1 Well3 of member one of Yingcheng Formation in Xudong area in Xushen Gas Field. (2) There mainly are cranny-center eruptions in volcanic reservoir of member one of Yingcheng Formation in Xudong area in Xushen Gas Field. The large territorial ruptures controlled the distributing of craters, and crater and volcanic eruption intensity dominated extended of stratum characteristics. Ancient landform and conformation evolvement also have some influences to stratum distributing characteristics. The key of foundation of stratigraphy trellis in large scale is the truly recognizing of the top and the bottom of volcanic reservoir of member one of Yingcheng Formation by organically unites of well data and seismic data. The boundaries of volcanic reservoir in aimed stratum in study area mainly represent onlap and truncation other angle unconformity surfaces. They mainly behave the abruptly change of number of GR and RT. (3) Numerous volcanic edifices and bodies were overlay each other in space and formed volcanic reservoir of member one of Yingcheng Formation in Xudong area in Xushen Gas Field. Recognizing and tracing volcanic bodies were similarity with it did about volcanic edifices. The only different things are that the scale of the former is more subtle than the latter. The boundaries of volcanic edifices always behaved sedimentary rock and crust of weathering and other marker beds. The boundaries of volcanic edifices and bodies are strong reflection events and entirely changes of different reflection wave groups and occurrence broken and continuous reflection wave groups interrupted abruptly and other characteristics. It is number saltation in well logging and lithology mutation in logging or structure changes in the same lithology. It behaves mutation of physical properties of porosity and permeability. (4) The boundaries of fine stratigraphic division and correlation of volcanic reservoir may through different volcanic edifices but couldn t through volcanic bodies. The volcanic stratum of member one of Yingcheng Formation in Xudong area in Xushen Gas Field was carved up to six layers of YC1I1 and YC1I2 and YC1I-II and YC1II1 and YC1II2 and YC1III from the top to the bottom. The volcanic stratum mainly represented mound characteristics which neared the craters. The surfaces of layers and the surfaces of volcanic bodies were basically unanimous in side direction. And the volcanic stratum mainly behaved samdwich characteristics which far away from the craters. The results of stratigraphic division and correlation of volcanic reservoir had preferable effects with lithology and lithofacies and dynamic development data. ACKNOWLEDGMENTS This research was sponsored by the Magnitude Project of Ministry of Science and Technology of China (No. 2008ZX ), the China Postdoctoral Science Foundation (No ) and Youth Innovation Fund of Research Institute of Petroleum Exploration and Development of PetroChina (No B-10-03). Thanks go to the following colleagues: Yongjun Wang, Min Tong and Jing Zhang in Research Institute of Petroleum Exploration and Development, PetroChina. REFERENCES CITED Chen, H. Q., Zhu, X. M., Microfacies Modeling in Fine Reservoir Description. Geological Science and Technology Information, 27(2): (in Chinese with English Abstract) Chen, H. Q., Zhu, X. M., Liu, C. L., et al., Characteristics of Sequence Stratigraphy of Thalassic Strata of L Formation in Deepwater Area in a Basin. J. Mineral. Petrol., 29(1): (in Chinese with English Abstract) Chen, Y. Q., Li, B. G., Classification and Correlation of Permian Volcanic Rocks in Mid-Tarim Area. Journal of the University of Petroleum, China, 28(6): 6 10 (in Chinese with English Abstract) Guo, X. R., Cheng, S. T., Liu, X., Division and Correlation of Substrata in Reservoir Description: The Substrata

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