中国天然气工业在改善我国能源结构、大力推动低碳经济发展过程中获得了前所未有的大发展.我国天然气资源丰富,目前已建成了鄂尔多斯、新疆2大油气区和四川、南海西部2大气区,天然气骨干管网逐步形成,天然气市场不断拓展,天然气工业体系初步形成.我国天然气资源分布具有明显的不均衡性,剩余资源量主要分布在岩性地层、前陆盆地冲断带、叠合盆地深层、成熟探区深层以及海洋等领域.从勘探的现实性看,碳酸盐岩风化壳地层油气藏、深层碎屑岩以及非常规油气等领域是未来天然气发展的重点,海相页岩气勘探突破、煤层气稳步发展,非常规天然气显现出良好的发展前景.从勘探发现潜力看,地层油气藏、深层、海域深水和致密油气是未来寻找大油气田的重点勘探领域.随着勘探程度的不断提高、勘探深度的不断增加,油气勘探成本总体呈现出明显的上升势头.天然气勘探新发现与储量增长更加依赖于理论技术进步,三维地震、水平井和压裂等工程技术作用更加凸显.通过增加天然气勘探开发投入、加强核心技术攻关,我国天然气工业仍将持续保持快速发展的良好态势.

distribution rules of volcanic reservoirs since volcanic reservoirs were first discovered as a special type of reservoir. Research at various levels has been conducted, including the development characteristics and distribution rules of volcanic rocks; eruption mode and eruption type of volcanic rocks; features of volcanic edifices; different types of volcanic facies and lithologies; characteristics; formation mechanisms; and distribution rules of pore structures in volcanic reservoirs, types and hydrocarbon-bearing properties of volcanic reservoirs, and types and hydrocarbon accumulation conditions of volcanic reservoirs. Current research activities, however, mainly focus on the type and genesis of the reservoir space, diagenetic evolution of the reservoir, and factors controlling reservoir development. Research on the volcanic reservoir formed mechanism is seldom conducted or needs to be strengthened. Purposeful research efforts should be made during hydrocarbon exploration for standardizing the lithology, classifying lithofacies, and naming volcanic rocks, as well as understanding the evolution mechanism of hydrocarbon accumulation, main factors controlling reservoir development, and the distribution of favorable reservoirs.

The geologic study of volcanic reservoirs focuses on the effective configuration relationship of the reservoir, hydrocarbon-generation assemblage, and trap. This chapter introduces the hydrocarbon source of volcanic reservoirs, major play types, and reservoir types of volcanic rock. Moreover, we discuss the oil and gas enrichment law of volcanic rock.

Global oil and gas fields of volcanic rock are primarily distributed in the Phanerozoic volcanic rock zone, which is intimately connected with the most active tectonic provinces in the world. The oil and gas fields in the Bohai Bay Basin, China, are associated with the Cenozoic volcanic massif; the gas fields in the Sacramento Basin, United States, intersect with or are superimposed on the modern crater. Both show that these oil and gas accumulations are intimately connected with volcanism. Volcanism can supply a great variety of oil and gas sources for volcanic rock plays, and sedimentary rock and volcanic rock can form a reservoir-caprock-trap assemblage, which is favorable for the formation of oil and gas fields.

Volcanic rock has special geophysical properties, such as strong magnetism and resistivity, and high density. Therefore, gravity, magnetic, and electrical nonseismic prospecting techniques play an important role in the comprehensive prediction of volcanic rock, which has already been proven to be effective in overseas and domestic experiences of volcanic rock exploration for half a century. In this chapter, we summarize the integrated gravity, magnetic, electrical, and seismic prospecting as a series of four steps, based on the volcanic hydrocarbon exploration in Songliao Basin and Junggar Basin. First, distributed provinces of volcanic rock are predicted based on gravimetric and magnetic data to determine target areas; a comprehensive evaluation is conducted based on seismic, electrical, drilling, logging, and geologic data to further confirm target areas. Second, seismic data are taken as the primary dataset combined with electrical and other data to describe the shape of the volcanic rock and predict the favorable target zones. Third, the volcanic reservoir is predicted using seismic attribute analysis, coherence volume, and poststack seismic inversion on the basis of seismic data combining with logging data. Fourth, fluid detection is conducted based on seismic or logging data to determine drilling targets with lower exploration risk. These four steps are generally mature techniques.

Volcanic reservoirs have become one of the major exploration areas in China. Since 2002, major breakthroughs and significant advances in exploration in volcanic rock have been made in both eastern and western China. Giant gas provinces with reserves scales of 3000-5000 × 108 m3 have been preliminarily discovered in deep layers of the Songliao Basin and at Ludong-Wucaiwan in the Junggar Basin. Exploration has also shown a reserves scale of 100 million tons in the Santanghu Basin. These indicate that volcanic rocks, as an exploration area with special lithology reservoirs, have become significant to practically increase and replace hydrocarbon reserves in China and promise a broad exploration potential.

Volcanic reservoirs, regarded as unconventional reservoirs with volcanic rock as the reservoir bed, have been widely discovered in many hydrocarbon-bearing basins at home and abroad for more than 100 years. Overseas volcanic reservoirs have experienced a long history of exploration with some discoveries of large oil and gas fields, but most of which were discovered by chance or in very localized areas. Volcanic reservoirs have not garnered much interest on the part of oil and gas explorers. However, in China, volcanic reservoirs have received more attention recently and have become one of the major targets for exploration. Hydrocarbon exploration has made breakthroughs in volcanic rocks in the deep Songliao Basin and the Carboniferous-Permian Formations in the Junggar and Santanghu Basins. Reserves have increased on a large scale, demonstrating the potential of oil and gas exploration in volcanic rocks.

Research Institute of Petroleum Exploration and Development, PetroChina, Beijing 100083, China)[Abstract]Carboniferour-Permian, Jurassic-Cretaceous and Paleogene-Neogene volcanic reservoirs have acted as the exploration play in China. Volcanic reservoirs located near the source rocks are the most beneficial for hydrocarbon accumulation, so the hydrocarbon-generation centers control the hydrocarbon distribution, and the volcanic reservoirs located far from the source rocks need through faults and the discomformities surfaces. The lava, volcanic breccia and volcanics located in weathered crust are the dominant reservoirs. In the rift basins of eastern China, volcanic reservoirs are mainly composed of lithologic and structural-lithological type and are formed near the source rock centers; in the basins of central and western China, volcanic reservoirs formed near or far from the source rocks, and stratigraphic reservoirs are formed along the uncomformity surfaces.

Large and extra-large oil/gas fields are mainly distributed in Tethys areas, passive margins, foreland thrust belts, and craton basins in the world. Unconventional oil/gas fields are mainly distributed in foreland slopes, basin (depression) centers, craton synclines, and tundra. Since the 21st century, the major exploration discoveries across the globe have been mainly concentrated in the deep water area of passive margins, carbonate rock, lithologic-stratigraphic zone, foreland thrust belt, mature exploration area, new basin and unconventional oil/gas reservoir (field). These major discoveries involve conventional and unconventional oil/gas resources. The conventional oil geology stresses the oil/gas migration and reservoir-forming rules in individual traps; the unconventional oil geology focuses on unconventional resources, reservoir, reservoir-formation and technologies. The geological features, classification program, research content, evaluation method and exploration phase of unconventional oil/gas reservoirs (fields) are different from those of conventional ones. Research should be strengthened on unconventional oil geology to develop unconventional oil geological theories.

Volcanic rocks are distributed widely in China, which are important exploration targets. By analyzing many discovered volcanic hydrocarbon reservoirs all over the world, the authors summarized the geologic characteristics of the formation of volcanic hydrocarbon reservoirs in China, and gave further exploration directions and advices. (1) There are mainly Carboniferous‐Permian, Jurassic‐Cretaceous, Paleogene‐Neogene volcanic rocks in oil‐ and gas‐bearing basins in China, which are mainly distributed in the Junggar Basin, Songliao Basin, Bohai Bay Basin, etc. There are mainly intermediate rocks and acidic rocks in east China, and intermediate rocks and basic rocks in west China. They primarily develop in intracontinental rift settings and island are environments. (2) Porefissure reservoirs are distributed widely in basins, which are volcanic rocks mainly in explosive and effusive facies. (3) Volcanic hydrocarbon reservoirs are chiefly near‐source lithostratigraphic hydrocarbon reservoirs, and the oil and gas accumulation is predominantly controlled by lithotypes, faults and structural positions. (4) Deep‐seated oil and gas reservoirs in the Songliao Basin and Carboniferous volcanic hydrocarbon reservoirs in the Junggar Basin are potential giant volcanic gas provinces, the volcanic hydrocarbon reservoirs in the Bohai Bay Basin and Santanghu Basin are favorable for oil and gas reserves increase, and volcanic rocks in the Turpan Basin, Sichuan Basin, Tarim Basin have exploration potentiality. (5) The technology series of oil and gas exploration in volcanic rocks have been preliminarily formed.

Volcanic hydrocarbon exploration in China has experienced three phases: accidental discovery, local prospecting, and all-round exploration. There are mainly Carboniferous-Permian, Jurassic-Cretaceous, Paleogene-Neogene volcanic rocks and lava, pyroclastics, and karst reservoirs in the oil- and gas-bearing basins in China. Volcanic rocks cannot generate organic hydrocarbons, and the combination of volcanic rocks, source rocks, and seals are the key controlling factor of the primary lava plays. The near-source play is most favorable for hydrocarbon accumulation. Distribution of oil and gas is controlled predominantly by the hydrocarbon generating center. The play requires communication with faults or unconformities. Near-source plays are in the faulted basins in eastern China. Structural-lithologic hydrocarbon reservoirs are formed in the higher place of faults and lithologic hydrocarbon reservoirs are formed on the slope. Two types of plays are developed in central and western China. The near-source play is most favorable for the formation of large stratigraphic hydrocarbon reservoirs.

On the basis of seismic,logging and drilling information,the property of the stratigraphic and lithologic reservoirs in the Lower Cretaceous of Erlian Basin were analyzed with the sequence stratigraphy.Three factors for controlling the structure of those reservoirs include the rift structures,the sand control patterns of slope break and the fault-transfer zones,which influence petroleum accumulation in this area.The rift structure can be divided into three types of single fault overlap,single fault trough and complex type.The slope break has six patterns,including steep slope fault scrap and nearshore subaqueous fans,steep slope fault ramp and nearshore subaqueous fans and turbidite fans,steep slope fault bench and fan-delta and turbidite fans,gentle slope and braided river delta and fan-delta,gentle slope flexure and fan-delta and turbidite fans,and gentle slope fault bench and braided river delta or fan-delta and turbidite fans.There are four types faults-transfer zones in Erlian Basin,such as fault bend type,fault fracture type,fault intersection type and fault trace rift type.The analyses of different factors for controlling the structures can provide some information for exploring of stratigraphic and lithologic reservoirs in Erlian Basin.