| The exploration and development of volcanic oil-gas reservoir as well as its related technologies have been achieved great progress in recent years. In particular, various achievements have been made in the aspects of volcanic lithology, volcanic facies, volcanic edifice, volcanic reservoir and its geophysical recognition. However, there are still many potential problems during the fine exploration and development of volcanic reservoirs in practical production, such as the following problems that encountered in the research process of deep volcanic reservoir in Wangfu Depression and Yingtai Depression, southern Songliao Basin.(1) The researches about distribution and Formation mechanism of the intermediate volcanic rocks and volcaniclastic sedimentary rocks reservoirs are relatively less.In current, most research so far was about acid volcanic rocks and basic volcanic rocks reservoir in southern Songliao Basin. But the research of intermediate volcanic rocks and sedimentary pyroclastic rocks were relatively less due to the lower distribution and relatively poor petrophysical property, especially about the distribution and Formation mechanism. Due to the lack of specific research and theoretical support, many achievements of acid and basic volcanic rocks were used in practical exploration and development of intermediate volcanic rocks and sedimentary pyroclastic rocks reservoirs Which can cause the reservoir characteristics and distribution cannot be understood clearly, and result in missing some relatively high quality reservoir.(2) The current standard classification of volcanic rocks reservoir which lack of different volcanic rocks standards and constraints of reservoir’s pore structure parameters is too general.There are many volcanic lithology were drilled in south Songliao Basin, such as rhyolitic volcanic rocks, trachyandesitic volcanic rocks, andesitic volcanic rocks, basaltic volcanic rocks and sedimentary pyroclastic rocks, all of them could form effective reservoir. It is difficult to get a better practical application effect, for the standard classification of the volcanic rocks reservoir was based on acid volcanic rocks. In practical production, people can only use general standard to classify and evaluate the volcanic rocks reservoirs, for lacking of the classification and evaluation standards of different volcanic rocks. Meanwhile, problems that hinder the fine exploration and development of volcanic reservoirs were encountered, such as the great difference between comprehensive interpretation of logging data and gas production test. In addition, the common classification and evaluation standard in the petroleum and gas industry are mainly based on parameters of porosity and permeability. For lacking of constraints of reservoir’s pore structure parameters, the classification and evaluation standard cannot be objectively and effectively show the true peotrphysical characteristics of various types of reservoir. Therefore, it is urgent to establish standards of different volcanic rocks, which based on qualitative and quantitative characterization of reservoir’s pore structure.To solve the above problems, this dissertation takes intermediate volcanic rocks reservoir in Huoshiling Formation, Wangfu Depression and sedimentary pyroclastic rocks in the 2nd member of Yingcheng Formation, Yingtai Depression as the research object. This dissertation based on the achievements of volcanic lithology, volcanic facies, volcanostratigraphic, pore structure characteristics of reservoir, reservoir controlling factor, classification and evaluation of reservoir, and combined with coring date, thin sections, analysis tests, well logging and seismic in order to analyse the pore characteristics of the reservoir according to its controlling factor and Formation mechanism, and establish the standards of different volcanic lithology. The research process, methods and main results are as follows:1. Reservior space characterization of reservoirBy using the data of cores, thin sections and SEM(scanning electron microscope) to identify and classify pore types of intermediate volcanic rocks reservoir in Huoshiling Formation, Wangfu Depression and sedimentary pyroclastic rocks in the 2nd Member of Yingcheng Formation, Yingtai Depression. Combining with data of plane porosity according to analyze the composition and distribution of pores in volcanic reservoirs. Using the curve and paramenters from mercury-injection test and NMR (nuclear magnetic resonance) experimental, qualitative and quantitative characterization about reservoir pore structure can be identified. In research area, there are many types of reservoir, and the most developed type is the secondary pores, and the reservoir has complex pore structure and strong heterogeneity.(1) Types and characteristics of reservior spaceThere are 3 main categories and 9 sub categories reservior space types of intermediate volcanic rocks reservoir in Huoshiling Formation, Wangfu Depression. The secondary dissolution pores and fractures are the main reservior space types, and their contribution of plane porosity is 41.75%and 35.30%. In different volcanic rocks, the types and development characteristics of reservoir space are also different. The main types of intermediate lava effective reservoir are primary pores, secondary dissolution pores and fractures. The main types of intermediate pyroclastic lava are secondary dissolution pores and fractures, and few primary vesicular pores. The main types of intermediate pyroclastic rocks are intergranular pores, secondary dissolution pores and fractures. In different volcanic subfacies, the types and development characteristics of pore are also different. Secondary dissolution pores and fractures developed in every subfacies, primary vesicular pores mainly developed in upper effusive subfacies and pyroclastic flow deposit of explosive facies, and intergranular pores mainly developed in air-fall of explosive facies. Based on statistical analysis of the reservoir space types, there are 4 categories combination types developed in intermediate volcanic rocks reservoir in Huoshiling Formation, Wangfu DepressionRespectively are combination types of primary pores, secondary pores and fractures, combination types of secondary pores, combination types of secondary pores and fractures, and combination types of fractures. The combination types of secondary pores and the combination types of secondary pores and fractures are the main combination types in the research area. Statistical data shows that the porosity of different combination types is basically identical, but there is a great difference about permeability. Among them, the petrophysical properties of reservoir is high that developed combination types of primary pores, secondary pores and fractures and combination types of secondary pores and fractures.There are 3 main categories and 10 sub categories reservior space types of volcaniclastic sedimentary rocks in the 2nd member of Yingcheng Formation, Yingtai Depression. Intergranular dissolution pores and intragrannular solution pores are the main reservior space types, and their contribution of plane porosity is 47.92% and 38.67%. There are some differences between volcaniclastic sedimentary rocks and sedimentary rocks, such as few primary vesicular pores that developed in the breccia of volcaniclastic sedimentary rocks. For more pyroclasts are developed in the volcaniclastic sedimentary rocks, that can be easily dissoluted and formed secondary dissolution pores. There are 4 categories combination types developed in of volcaniclastic sedimentary rocks in the 2nd member of Yingcheng Formation, Yingtai Depression. Respectively are combination types of primary pores, secondary pores and fractures, combination types of secondary pores, combination types of primary pores and secondary pores, and combination types of fractures. The combination types of secondary pores and the combination types of primary pores and secondary pores are the main combination types in the research area. Statistical data shows that the petrophysical properties of these volcaniclastic sedimentary rocks is relatively low, but the petrophysical properties of reservoir is relatively high that developed combination types of primary pores, secondary pores and fractures and combination types of primary pores and secondary pores.(2) Characteristics of reservoir’s pore structure11 parameters that selected out from mercury-injection test and NMR experimental were selected for quantitative analysis of the pore structure in different volcanic rocks, such as permeability, porosity, displacement pressure, maximum mercury-injection saturation, average radius of pore throat, sorting coefficient, uniformity coefficient, structure coefficient and movable fluid saturation. Statistical data shows that the characteristics of reservoir’s pore structure in different volcanic rocks are also different. Therefore, in order to improve the accuracy and effectiveness of reservoir classification and evaluation, we need to evaluate the volcanic reservoir in different volcanic rocks with the constraints of reservoir pore structure parameters. The mercury-injection curve is divided into 5 types according to the curve shape and its pore structure significance meanwhile the NMR experimental curve is divided into 10 types, for qualitative analysis of the pore structure in different volcanic rocks. Moreover, quantitative parameters of every curve type are statistied and analyzed. Usually, high quality reservoir developed in the volcanic rocks which mercury-injection curve type are A or B. The volcanic rocks which mercury-injection curve type are C or D can form effective reservoir or potential reservoir. The results of gas production test often shown dry layer in the volcanic rocks which mercury-injection curve type was E.2. Reservoir distribution regulations of the intermediate volcanic rocks and the effects of volcanostratigraphic boundary controlled reservoirBy using coring data, thin sections, measured and logging physical properties, logging interpretation, gas production test and 3D data of seismic, According to the relationship between volcanic rocks and reservoir petrophysical properties, volcanic subfacies and reservoir petrophysical properties, buried depth and reservoir petrophysical properties, volcanostratigraphic boundary and reservoir, volcanic edifice and reservoir in basin to analyze the reservoir distribution regulations of the intermediate volcanic rocks and the effects of volcanostratigraphic boundary controlled reservoir(1) Relationship between intermediate volcanic rocks and reservoir petrophysical propertiesThere are 9 types of volcanic rocks developed in the intermediate volcanic rocks reservoir in Huoshiling Formation. The reservoir with high proportion of effective reservoir is developed in trachyandesite, trachyandesitic tuff, trachyandesitic tuff lava and trachyandesitic breccia lava. The reservoirs with high petrophysical properties are developed in andesite, andesitic tuff, trachyandesitic tuff, trachyandesitic tuff lava and trachyandesitic breccia lava. Considering the difference of statistical data, the intermediate volcanic rocks can be classified into 3 categories. The first category is trachyandesite and trachyandesitic breccia lava which with high proportion of effective reservoir and large thickness of development. They are the focus of exploration and development in the future for easily to form high quality reservoir. The second category is andesite, andesitic tuff, andesitic tuff lava, trachyandesitic tuff and trachyandesitic tuff lava which with high proportion of effective reservoir but small thickness of development. The third category is trachyandesitic breccia and andesite breccia with lower proportion of effective reservoir and petrophysical properties which is hard to form reservoir.(2) Relationship between volcanic subfacies and reservoir petrophysical propertiesThere are 3 facies and 7 subfacies developed in the intermediate volcanic rocks reservoir in Huoshiling Formation. There is a significant correlation between volcanic subfacies and reservoir petrophysical properties. The petrophysical properties of each facies become higher from volcanic vent facies, effusive facies to explosive facies. It can be classified into 3 categories according to the characterstics of reservoir petrophysical properties. The petrophysical properties of upper effusive facies and air-fall of explosive facies are highest, while base surge deposit of explosive facies and middle effusive facies are higher, and the other subfacies are lower.(3) Relationship between buried depth and reservoir petrophysical propertiesBased on the relationship between buried depth and petrophysical properties by measuring and logging data, there is a trend showing that the petrophysical properties become lower with the buried depth increasing, however, few abnormal high petrophysical properties zones can also exist (e.g.2350-2500m,2700-2950m, 3450-3600m).(4) Relationship between volcanostratigraphic boundary and reservoirBased on coring data, thin sections, physical properties and the T2 spectrum of nuclear magnetic logging as well as the classification of volcanostratigrahic boundary and logging identification, it’s possible to discuss reservoir Formation mechanism relationship through volcanostratigraphic boundary and reservoir. The volcanostratigraphic boundaries of the Huoshiling Formation in Wangfu Depression are divided into 2 grades:the eruptive interval unconformity boundary (EIUB) was the primary boundary, and the secondary boundary consists of eruptive conformity boundary (ECB) and eruptive unconformity boundary (EUB). The reservoir is closely related to volcanostratigraphic boundary, the higher physical properties get, the closer reservoir to EIUB is, or vice versa. The high-quality reservoir was developed within 30m away from EIUB. There will form a relatively better reservoir with high petrophysical properties when the ECB and EUB were enriched in a certain thickness. Types and distribution of volcanostratigraphic boundary controlled the development of pores and the distribution of reservoir. The reservoir under volcanostratigraphic boundary contains 3 belts vertically:secondary dissolved pores development belt, primary pores development belt and relative tight belt. The EIUB controlled the development of the secondary dissolved pores to form a high-quality reservoir that distributed along itself. The primary pores are enriched to form the relatively better reservoir when the ECB and EUB were enriched. By combining with the exploration practice in the Wangfu Depression, the volcanic rocks under volcanostratigraphic boundary can be served as a favorable reservoir of natural gas, especially the EUIB area.(5) Relationship between Volcanic edifice and reservoirThere are 5 types of volcanic edifice developed in the intermediate volcanic rocks reservoir in Huoshiling Formation, namely trachyandesitic lava volcanic edifice, andesitic lava volcanic edifice, trachyandesitic pyroclastic volcanic edifice, andesitic pyroclastic volcanic edifice, trachyandesitic lava volcanic edifice and composite volcanic edifice. The petrophysical properties of the composite volcanic edifice is higher than the trachyandesitic pyroclastic volcanic edifice when the trachyandesitic lava volcanic edifice is lower than the above two types. The andesitic lava volcanic edifice and the andesitic pyroclastic volcanic edifice cannot be evaluated without date and development thickness. With the volcanic edifice identified above, the author divided the volcanic edifice into volcanostratigraphic lava unit and volcanostratigraphic pyroclastic unit according to the volcanostratigraphic boundary. It is found by analysis that the more volcanostratigraphic boundaries in volcanic edifice, the better reservoir petrophysical properties of volcanic edifice become, which means the volcanostratigraphic pyroclastic unit is the relatively better volcanostratigraphic unit of reservoir.3. The controlling factors and the genetic analysis of abnormal high petrophysical properties zones of volcaniclastic sedimentary rocksIt can be seen from the relationship between buried depth and measured petrophysical properties, there is a trend showing that the petrophysical properties become lower when the buried depth increasing, however, few abnormal high petrophysical properties zones also exist. The author studied the relationship between lithologic features and reservoir, sedimentary micro-facies and reservoir, diagenesis and reservoir according to analysis of the control factors and the genetic analysis of abnormal high petrophysical properties zones of volcaniclastic sedimentary rocks.(1) The influence of lithology characteristics to the physical properties of the reservoirBased on the relationship between lithology characteristic and reservoir petrophysical properties, the petrophysical properties of the volcaniclastic sedimentary rocks with larger volcano pyroclastic particles are higher than the volcaniclastic sedimentary rocks with less volcanic pyroclastic particles. For there are more opportunities to the retention of primary porosity and the Formation of secondary porosity, and the intergranular dissolution pores are larger in the volcaniclastic sedimentary rocks with larger volcano pyroclastic particles. The characteristics of reservoir’s pore structure show that, the pore structure parameters of the volcaniclastic sedimentary rocks with larger volcano pyroclastic particles are overall better, though the separation coefficient is not in order. The volcaniclastic sedimentary rocks with high content feldspars and cuttings of volcanic pyroclastic are easily to form high-quality reservoir, for they are easily to be dissoluted. The physical properties of volcaniclastic sedimentary rocks with high content quartz that buried depth more than 3100m are lower, for the quartz overgrowth, compaction diagenesis and weak dissolution of quartz. In a word, the volcaniclastic sedimentary rocks with high content feldspars and cuttings of volcanic pyroclastic are easily to form high-quality reservoir than the physical properties of volcaniclastic sedimentary rocks with high content quartz.(2) The relationship between sedimentary micro-facies and reservoir physical propertiesThere are 4 sedimentary micro-facies of fan delta facies developed in the 2nd member of Yingcheng Formation, Yingtai Depression, respectively are inter-lobe, slide gravity flows deposits, underwater distributary’s channels and estuary dam sedimentary micro-facies. There are some differences during the development of effective reservoir of different sedimentary micro-facies, for the differences of particle size and composition of clastic particles caused by the differences of hydrodynamic condition in the transportation process of clastic particle will influence the Formation and retention of primary porosity and the Formation of secondary porosity. According to the petrophysical property analysis, the petrophysical property of gravity flows deposits sedimentary micro-facies is the best with more coarse-grained clastic, it is consistent with the results of the studies on the size and composition of the clastic particles. The petrophysical property of underwater distributary’s channels is better when other sedimentary micro-facies are poor.(3) The controlling effect of diagenesis on reservoirAccording to the data of Ro and X-ray analysis of volcaniclastic sedimentary rocks in the 2nd member of Yingcheng Formation, Yingtai Depression, it has entered the stage B of middle burial to deep burial stage, and the main diagenesis consist of compaction, dissolution, infilling activities, devitrification and recrystallization and mineralization of clay. In the process of burial diagenesis of volcaniclastic sedimentary rocks, compaction was destructive diagenesis for it could cause rock densification. Infilling diagenesis was destructive diagenesis for the intergranular pores; intergranular pores and fracture were filled or half-filled by Zeolite, Calcite, Chlorite and other minerals. The clay minerals developed in the reaserch area consist of Kaolinite, Illite, Chlorite and Illite-Smectite clay minerals which can inhibite or promote to effective reservoir Formation. On one hand, the clay minerals filled into primary porosity and caused it smaller; on the other hand, there are many intercrystalline micropores between the clay minerals that could provide a certain rate of plane porosity. Devitrification and recrystallization main developed in the deep burial stage, it has improvement effect to the reservoir. According to observation under microscope of thin sections in the reseach area, the secondary dissolution pore developed widespread. The deep dissolution is the direct cause of abnormal high petrophysical properties zones in volcaniclastic sedimentary rocks, and the dissolution liquid comes from organic matter of mudstone which developed in multi-layered with volcaniclastic sedimentary rocks. The organic acidic fluids that generated from the process of organic matter’s thermal evolution entered the reservoir, dissoluted the cement and the clastic particles to form secondary dissolution pores, and improved the physical properties of the deep volcaniclastic sedimentary rocks reservoir in basin.(4) The genetic analysis of abnormal high petrophysical properties zones of deep volcaniclastic sedimentary rocksBased on the analysis above, the deep dissolution is the main and direct cause of abnormal high petrophysical properties zones in volcaniclastic sedimentary rocks, and the dissolution liquid comes from organic matter of mudstone which developed in multi-layered with volcaniclastic sedimentary rocks. The organic acidic fluids which generated from the process of organic matter’s thermal evolution entered the reservoir, dissoluted the cement and the clastic particles to form secondary dissolution pores, and improved the physical properties of the deep volcaniclastic sedimentary rocks reservoir in basin. In the process of burial diagenesis, the composition and structural characteristics of clastic particles is the internal control factors of the abnormal high petrophysical properties zones in volcaniclastic sedimentary rocks and the burial diagenesis process is the external control factors.4. Reservoir classification and evaluationAccording to the analysis results of petrophysical properties, diagenesis, reservoir space characterization, as well as qualitative and quantitative characterization of pore structure, the overall quality of reservoir can be described to cluster analyze the relative different reservoir quality between various lithologies. After cluster analysis, the reservoir of the volcanic rocks that consist of 2 main categories and 12 subcategories can be divided into 18 types. Also, the typical examples of pore structure and well logging characteristics for 12 categories reservoirs in the research area are discussed respectively. It is necessary to study on the evaluation and classification of reservoir with the constraints of pore structure’s qualitative and quantitative characterization through analyzing. There are 4 methods were used to calculate the cut-off value of effective reservoir in intermediate volcanic rocks and volcaniclastic sedimentary rocks. The cut-off value of porosity and permeability respectively are 4.70% and 0.003 ×10-3μm2 in intermediate volcanic rocks reservoir, while the cut-off value of porosity and permeability respectively is 3.20% and 0.001 ×10-3μm2 in volcaniclastic sedimentary rocks. According to the results of cut-off value and cluster analysis of reservoir, the standard of reservoir classification and evaluation about 2 main categories and 6 sub categories volcanic rocks can be established in the research area. |
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