Mesozoic faults at the eastern margin of the Songliao Basin were well developed. Based on detailed field geological survey of the Yingcheng Formation at the eastern margin of the Songliao Basin，the nature, attitude and spatial and temporal distribution regularities of these faults were systematically described. The formation of these Mesozoic faults was divided into four epochs, namely, Later Variscan-Indosinian, Yingcheng, the last stage of Yingcheng epochs and the late stage of the Later Cretaceous. Based on the distribution regularity of the craters in the Yingcheng Formation, the concealed faults of the Yingcheng epoch were identified for the first time and were considered to have controlled the formation and distribution of the volcanic rocks of the Yingcheng Formation. The NS trending faults of the Yingcheng epoch discovered in the area could also sever as a comparison for the NS faults of the Yingcheng Formation in the Qingshen gas field in the Xujiaweizi area. It was suggested that and alternative tectonic stress field of EW trending extense depression and of EW trending compressive thrust existed in the Yingcheng epoch. A NE-SW trending tectonic stress field was introduced by two left-lateral strike-slip faults called the Jiamusi-Yitong and Siping-Harbin respectively at the final stage of the Yingcheng epoch, and the resulted stress field in turn controlled the intrusion of some NE trending basic dikes and development of several NE and NW trending strike-slip faults. It was believed that the faults in the study area could be compared with those in the Xujiaweizi area of both the Yingcheng epoch and of the final stage of the Yingcheng epoch, which set a basis for predicting the distribution regularities of volcanic rock reservoirs in the Qingshen gas field.

Compared with modern volcanic eruption types and volcanic structures, two kinds of paleo-volcanic edifices of the lower Cretaceous Yingcheng Formation (K₁y) periods were recognized and described in the Songliao Basin based on their lithology, facies and vertical successions. They are basaltic and rhyolitic respectively. The basaltic volcanic edifices of the K₁y are mostly shield volcanoes, with features of shield shape and gentle slopes less than 10°, of volcanic thickness of 200 m to 500 m, and of height difference from 100 m to 250 m. Vertical succession from bottom to top is from pillow lava and aa (with thickness proportion of 30%), to lava with vesicle and amygdule and also massive lava (with thickness proportion of 70%). Like Hawaiian, eruption of the basaltic type is mostly effusive and hydrothermal breccias were often developed around the conduit. On the other hand, the vertical sequence of the rhyolitic volcanic edifices is with three layers in a 300 m to 700 m interval. The bottom is composed mostly of pyroclastic breccia (explosive lava) (30% thickness), characterized by base-surge deposits with Pelean eruption. The middle layer is composed mostly of effusive rhyolites with vesicles, lithophysas and flow banding (60% thickness). Domes of extrusive perlite can also be found in the middle member, especially around calderas. The eruption type is Strombolian-like. The top layer is composed mostly of explosive granule tuff (sometimes stratiform) (lacustrine deposit of ash, 10% of thickness), with an eruption type of Plinian. Rhyolitic edifices is characterized by mound shape, relative evaluation of 200 m to 300 m and slope often more than 15°, thus belonging to stratovolcanoes.

According to eruptive scale illustrated by drilling lithology, facies characteristics and seismic data, early Cretaceous volcanic edifices of Yingcheng Formation in Xujiaweizi faulted depression, Songliao Basin were classified into pyroclastic volcanic edifice, lava volcanic edifice and compound volcanic edifice. The facies composition of pyroclastic volcanic edifice was listed as fellows: 9.3% for volcanic vent facies, 55.3% for explosive facies, 29.2% for effusive facies, 1.4% for extrusive facies and 4.8% for volcanic sedimentary facies. The pyroclastic volcanic edifices is 0.5-1.5 km wide and 50-220 m thick. The facies composition of lava volcanic edifice was 8.1% for volcanic vent facies, 23.4% for explosive facies, 62.6% for effusive facies, 5.1% for extrusive facies, and 0.8% for volcanic sedimentary facies. The lava volcanic edifices is 1-2 km wide and 200-300 m thick. The facies composition of compound volcanic edifice was 4.9% for volcanic vent facies, 34.4% for explosive facies, 56.8% for effusive facies, 2.6% for extrusive facies and 1.3% for volcanic sedimentary facies. The compound volcanic edifices is 2-4 km wide and 300-450 m thick. The scale of reservoir flow unit is controlled by subfacies of volcanic edifices. So the scale of reservoir flowing unit is various for each volcanic edifice, pyroclastic volcanic edifice is 0.3-1.5 km in width and less than 60 m in thickness, lava volcanic edifice is 1-2 km in width and less than 80 m in thickness, compound volcanic edifice is 1.5-3.0 km in width and less than 100 m in thickness. So the distance of wells and hydraulic fracturing plan are different in each kind volcanic edifice during the development.

Both lower Cretaceous Yingcheng Formation and upper Jurassic Huoshiling Formation are partially composed of volcanic rocks in southern Songliao Basin. In Dongling area, most volcanic rocks of Yingcheng Formation are acidic and 73% of them belong to explosive facies while most volcanic rocks of Huoshiling Formation are basic. The volcanic rocks in Huoshiling Formation were divided into upper and lower series. 67% volcanic rocks of upper series are explosive facies and 59% volcanic rocks of lower series are explosive facies. Lenticular and mound shape, mid-strong or weak amplitude, low frequency, chaotic-bad continuity and diachronous phenomenon are the characteristics of seismic reflection for acidic rocks. The top boundary of acidic rocks shows a strong reflection. Eyeball and mound shape, weak reflection, worm like, low frequency, chaotic and bad continuity are characteristics of seismic reflection of basic rocks. Volcanic rocks were recognised by using inversion of simulated AC curve. The results showed that fault F₁ controlled the thickness of volcanic rocks and thicker in the west and thinner in the east. The thickest was around well SN109. Cones of volcanic edifices were recognised by using trend surface of structure and 3D slice methods. Two conedeveloped areas have been found in Huoshiling Formation. The cones distributed in 56 km² with structural amplitude of 547 m. Volcanic vent facies and extrusive facies were recognised with dip angle method based on the geophysical model of volcanic edifices. Explosive facies and effusive facies were recognised with waveform classification method. Integration of the dip angle method and waveform classification method recognises volcanic facies. The upper subfacies of effusive facies and volcanic vent facies well developed in the middle area of Huoshiling Formation. The cone-developed area is the first-rank target of volcanic prospect because of the thickest volcanic reservoirs and perfect permeability and porosity.

It was the first time to carry out the systematical statistical analysis on the joint occurrence, scale, width, density and distribution regularities to elaborate the reservoir significance. According to the analysis of joint position, the inter-cutting relationship and the regional tectonic settings, the formation epochs of joints in the target area were divided into three epochs, namely, Yingcheng epoch, the last stage of Yingcheng epoch and the late stage of K₂.By using conjugate joint occurrence and joint nature, basing on the statistics and calculation, Yingcheng epoch had nearly EW direction tectonic stress field with stretch and compression alternatively， NE-SW direction tectonic stress field was formed in the last stage of Yingcheng epoch， NW-SE direction compressional tectonic stress field was formed in the last stage of K₂.It was considered that the joint formation and distribution of Yingcheng Formation were mainly related with the first two compressional tectonic stress fields. The joint distribution regularities of Yingcheng Formation in Xujiaweizi region were predicted, which provides the visual correlation for the study on the distribution regularities of natural gas reservoir.

There are two types of diabaseprophyrite dikes in the third member of the Cretaceous Yingcheng Formation at the Shanghewan area in the southeastern uplift of the Songliao Basin. One type of diabaseprophyrite was emplaced in the NE30°-35° trending trackingexpansion joints, and contained dikes of 1-5 m in width, 75°-88° in dip angle and showed indented contact between the dikes and the county rocks. Another type of dikes was emplaced in the 40°-45° direction shear joints, with the dikes being 2-10 m in width, 75°-88° in dip angle and showing lowangle lineation or striation in the slippery boundary between the dikes and the county rocks. There are strong to weak schistosity from rim to centre in all the dikes. The chemical compositions of the dikes are similar to that of the basalts. However, the dikes show secondary changes, including hypo-calcspar and crystallite biotite, indicating fluid-rock metasomatism. The diabaseprophyrite dikes recorded some important events happened in the area when the terminal deposition of the Cretaceous Yingcheng Formation took place in this area-NE-SW compressive tectonic stress and basic magmation. The research for the incursion and deformation of the dikes indicates that they were controlled by the Jiamusi-Yitong faulting and was under compression after intrusion of dikes. The study on the geological characteristics of the diabaseprophyrite provides some important information to the relations between the original fracture-cracks in dikes and their reservoir significance.

A new method is proposed here to identify the volcanic subfacies/facies with the cuttings. The general flowchart is true cuttings selection→cutting thin section preparation→thin section observation with microscope→subfacies/facies identification. The volcanic subfacies/facies finally is identified according to the typical characteristics of lithology, structure and texture observed under the microscope. The resolution equals to the cutting sampling interval (1 m, in general). The accuracy is more than 90% compared to the core observation. This method was effective to verify the lithology as well as the volcanic facies. It has been proved as an effective way to promote the resolution of inter-well lithology and facies correlation based on the applications in 15 wells in Dongling, Southern Songliao Basin.

Stratigraphical correlation is performed on 20 cross and drilling sections at the southeastern margin of the Songliao Basin and in the Xujiaweizi faulted depression. The Yingcheng Formation could be divided into five lithologic members and considering that member 1- member 4 have been in usage in the Xujiaweizi faulted depression, the author have termed the five lithologic members as: lower member (K₁y^low), member 1 (K₁y¹), member 2 (K₁y²), member 3 (K₁y³) and member 4 (K₁y⁴), in order not to cause more confusion. The lower member consists mostly of andesite basalt, andesite, andesite tuffaceous with conglomerate, sandstone, siltstone and mudstone as interlayers, with Yingcheng 343 drilling hole profile as its standard section. Rhyolite, perlite and rhyolite volcaniclastic rocks dominate in member 1. Member 2 is mostly of clastic rocks, including conglomerate, sandstone, siltstone, mudstone with tuff as interlayers in the lower part and rhyolitic volcaniclastic rocks at the top of the member. Member 3 is composed of basalt, basaltic tuffaceous rocks at the lower and middle parts while at the top of the member of intebedding of the intermediate with acidic volcanic rocks. Xieweibagou-Guanmashan-Tuanjie crosssection can be selected as the standard section of member 1, member 2 and member 3. Member 4 consists mostly of conglomerate, samdwiched in sandstone and mudstone, with the Xushen 1 drilling hole profile as its standard section. Member 4 only exists in the Xujiaweizi faulted depression.

According to field geological section survey and in door thin-section identification, polymictic conglomerate of the 1st member of the Yingcheng Formation contain 4 types of cementation: magma, micrite, tuffaceous and sand and politic. Magma cementation is a main cementation type in the Songliao Basin. The gravels in the polymitictic conglomerate are quite complex. Most of gravels are granite derived from the base of the Songliao Basin and from Permian metamorphic rocks. In-situ volcanic rocks are secondary in abundance. The gravels are poorly sorted. Their psephicity is from moderate to fine, with sub-round and sub-angular shapes being mostly common. From base to active volcanic center, the amount of the mexotic gravels of polymictic conglomerate is decreasing, and the in-situ volcanic gravels are increasing gradually. Matrix composition is also mulriple. At bottom it is argillo arenaceous, changed into trffaceous upwords and became magmatic at the top. Unconsolidated or semi-consolidated sand-gravel deposits accumulated in some sediment environments such as alluvial fan, braided river and so on, were carried by pyroclastic flow or lava flow during volcanic eruption periods to form mixtures with pyroclastic flow, lava flow and waters. After cooling and compaction, the polymitic conglomerates were formed as a result. Since the conglomerates were often found near the bottom of the volcanic sequence at the fault basin brink, it reveals that the origin of conglomerate is relative both to tectonic activity and volcanic activity, and they are special products at the early stage of the volcanic cycle.

Rhyolite with columnar joints has been found in the lower Cretaceous Yingcheng Formation, in an uplift area of the southeastern Songliao Basin. The columnar joints in rhyolite are primary structural joint developed in a sub-volcanic sub-facies of volcanic conduit (extrusive) facies. The joints seen include horizontal, inclined and vertical ones. Their cross sections developed are anomalous tetragonal, pentagonal or hexagonal and are of medium to small size. Crypto-explosive breccia structures were well developed. The diameter of prisms is in proportion to the size of micro-fabric phenocryst. The primary genetic mechanism for the joints is the condensing shrinkage. Controlled by different factors, the eventual shapes of columnar joints are quite varied.

Different types of perlite have been found in the Yingcheng coal mine，Jiutai . Based on the composition and structure, perlite in the mine can be classified as strong altered, rhyolitic structure, rhyolitic and pearl structure interbedded, porphyroblast containing and silicated perlites. According to their altered stages and products, perlite in the mine can also be classified as unaltered(normal), weak montmorillonitized, strong montmorillonitized and silicified-montmorillonitized perlites. The formation processes of the perlite in the area could be suggested as the followings: after being exhausted on the surface, the lava falls into water directly, where it was condensed and consolidated because of plastic glass hydration. And its alteration process was promoted by the presence of the alkaline aqueous medium. The perlite in the area is of characteristics of decreasing reservoir significance with increasing alteration.

The Beishan perlite in the Santai area belongs to the first member of the Yingcheng Formation and is exposed in an area of 0.62 km², and its thickness is over 30 m. The perlite is associated with bentonite, hydrothermal breccia, rhyolite in typical geological sections. The perlite can be divided into pillow and orbicular, fluidal massive，breccia perlites and perlitic agglomerate. The perlite contains phenocrysts of amphibole and pyroxene, and its groundmass is of clear spherulitic and microlitic textures, indicating intensive devitrificaltion. In ascending order, the rock sequence is perlite→bentonite→hydrothermal breccia→rhyolite, and the facies sequence is volcanic conduit facies→effusive facies. The perlite is formed by fast under water cooling. The petrogenesis of perlite consists of the fellowing three stages: the first stage is a collapse volcanic lake-explosive phase. A collapse volcanic lake was formed during the early Cretaceous in the Santai area and tuff with developed horizontal beddings were formed in the stage. The second stage includes three substages. Substage of extrusion under water was featured by the volcanic eruption happened in the collapse volcanic lake, and large amount of perlite (volcanic glassy lava ) and some rhyolite lavas were formed because of quick cooling of magma under water of the basin in the substage. The hydrothermal substage was featured by the formation of rhyolitic hydrothermal breccia while the explosive-effusive substage is characterized by volcanic agglomerate, tuff and rhyolite. The third stage is called partial bentonitie stage. The perlite was hydrated by the groundwater of atmospheric origin under alkaline condition during inter-volcanic eruption stage. Only partial perlite (surface or fractures) was altered into bentonite because there was not enough water medium under relatively closed condition for the perlite.

The main types of volcanic rocks of the Yingcheng Formation in Santai area, southeastern uplift of the Songliao Basin are perlite, rhyolite, hydrothermal breccia, breccia conglomerate, tuff and so on. The devitrification of perlite and rhylolite is obvious. It can be found under microscope that the devitrification of perlite is of three phenomena: crystallite, skeletal crystal (microlite) and spherulitic while the devitrification of rhyolite is mainly of spherulitic. The development process of the devitrification is featured by a gradual increasing trend from crystallite to skeletal crystal (microlite) and finally to spherulitic. The formation and intensity of devitrification are related not only to the rock composition, but also to the formation and development of cracks. Laboratory tests indicate that the density of perlite, in the range of 3.13%-8.65%, is lighter after intense devitrification and is heavier with slight devitrification. Assuming a closed system, the decreasing density of rocks is corresponding to an increase in porosity of the rocks. Devitrification processes in the area can improve the reservoir properties of the glassy volcanic rocks.

The lithological types of the first member of Yingcheng Formation of the Lower Cretaceous in Santai area consist of crypto-explosive breccia, breccia lava, welded breccias, perlite, rhyolite and tuff. Volcanic facies are volcanic conduit facies, extrusive facies, effusive facies and explosive facies. Geological evidence for determination of the position of ancient crater are lithological character，facies and distribution of perlite and rhyolite. Whole volcanic edifice can be subdivided into the central facies，the proximal facies and the distal facies. The central facies, namely as volcanic vent facies， includes volcanic conduit facies and extrusive facies. The proximal facies is effusive facies, the distal facies is explosive facies. Faciessequence is crypto-explosive breccia subfacies of volcanic conduit facies, middle subfacies of extrusive facies, inner subfacies of extrusive facies, lower subfacies of effusive facies, middle subfacies of effusive facies and pyroclastic flow deposits of explosive facies. The permeability and porosity of the proximal facies is more predominant than the central facies. The upper subfacies of effusive facies is the best reservoir.

Recent geological survey on the outcrops of the Yingcheng Formation exposed in the Liutai area at the eastern margin of the Songliao Basin and related laboratory analysis reveal that a set of seemingly normal clastic sedimentary rocks in the second member of the Yingcheng Formation is in fact a set of transitional rocks between lava and normal sedimentary rocks. This succession of rocks contain clastic lava, tuff, tuffite, tuff clastic rock and normal clastic rock, which suggest they were formed in a transitional environment of volcanic slope to fluvial plain or lake. There are 4 end members of volcanic clasts, including catapult airfall, ejection airfall, base surge and volcanic clasts flow. If the volcanic clasts were deposited on volcanic slope and/or fluvial plain, they would occur in the 4 faceis mentioned above or in alluvial fan and braid stream. If the volcanic clasts were deposited in lake, they would occur in delta, fandelta, shallow-deep lake, and swamp. The architecture of facies could present the forming process of volcanic eruption-clastic accumulation. The characteristics of sedimentary cycles of the second member of the Yingcheng Formation show that there are 3 kinds of basin fillings: sedimentary-valcanic, sedimentary and volcanic. The entire succession should be from coarse clastic rocks to volcanic rocks and volcanic clastic rocks and to fine clastic rocks, corresponding to rifting, volcanic activities and sedimentation in rift basin respectively.

A set of conglomerates of alluvial fan occurred in the second member of Yingcheng Formation of Liutai, southeast margin of Songliao Basin. According to different origins, it can be divided into three types: debris flow deposits, channel deposits and sheetflood deposits. The debris flow deposits is the best developed. Based on the study of components, textural maturities and grain size distributions, and by using the experiential formula, it has been found that the debris flow deposits in this area were redeposited and occurred above the water. Channel deposits and sheetflood deposits were preserved much less than debris flow deposits. Maybe they had been well developed in single cycle, however, they were eroded by the violent debris flow of the next cycle. The convergence direction of bedding and the strike of petrified wood in the channel deposits and sheetflood deposits show that the paleocurrent flowed from northwest to southeast. The direction of paleocurrent indicates that the provenance of conglomerate is Beishan which locates in the northwest of the study area. Based on the result, the origin model of gravelly alluvial fan has been set up.

The volcanic rocks of the Yingcheng Formation in the Songliao Basin were formed by multiple and intermittent eruptions. Triple division was applied in the basin volcanic rocks researches: volcanic cycle, stage and facies. A volcanic stage was defined as volcanic rock assemblages formed by a concentrated volcanic activity at certain eruption center during its regular changes on materials, components, eruption behaviors and intensity. And a volcanic cycle includes one or several stages. Geological and geophysical methods were used to divide volcanic stages, including volcanic lithology and facies analysis from logging and seismic information. Special geological interfaces were identified. The measured section of the Yingcheng Formation has been divided into five volcanic cycles and thirteen stages.

Yingyi-D1 well, an exploratory well, was drilled to reveal the insider of standard section of Yingcheng Formation in 2006. Volcanic lavas, pyroclastic lavas, pyroclastic rocks and sedimentary pyroclastic rocks have been found in this well. The volcanic lavas include rhyolite, pitchstone, perlite and basalt. Pyroclastic lavas are consisted of breccia lava, tuff lava and ignimbrite. Pyroclastic rocks are mainly composed of volcanic breccia and tuff. Sedimentary pyroclastic rocks are mainly sedimentary tuff and sedimentary volcanic breccia. They mainly belong to effusive facies, explosive facies and volcanogenic sedimentary facies. The average porosity is 15.17％ and the average permeability is 1.51×10^-3μm². The porosity is linearly correlated to permeability. Based on the mercury injection capillary pressure data, the pore structures could be classified into six types. Synthetical evaluation of porosity & permeability and pore structure, the reservoirs were classified into four types. Type I is a perfect reservoir with high to super-high porosity and super-high permeability, coarse throat dominating. Type Ⅱ is good reservoir with high porosity & permeability, fine throat dominating. Type Ⅲ is a medium reservoir with medium porosity, medium permeability and fine throat. Type Ⅳ is a poor reservoir with medium to low porosity, low permeability and fine throat.

The whole coring Ying-3 D1 well was drilled in the standard section for investigating of the upper two members of Yingcheng Formation. The overall thickness of the third member is 205.70 m and the drilled thickness of the second member is 48.75 m (unpenetrated). There are mainly five types of volcanic rocks including lava，pyroclastic lava，pyroclastic rock，sedimentary pyroclastic rock and sedimentary rock. Volcano eruptions in this well have been divided into three cycles and ten periods. The reservoir spaces have been divided into four types and eleven subclasses. Further more, there are four combination patterns of reservoir spaces. The most favorable is pores directly connect to the fissures. Four types of pore distribution and seven types of pore structures have been recognized with core observation, microscope image analysis and mercury intrusion method. The single-bias with coarse-kurtosis and double kurtosis type have the best pore distribution. The best pore structure is of the low displacement pressure-coarse pore throat.

The 3rd member of Yingcheng Formation was detailed studied by large scale mapping of lithology and lithofacies, 2D surveying of small lithology and lithofacies section and identifying rocks.The 3rd member of Yingcheng Formation contains 2 cycles which changed from intermediate-basic rocks to intermediate-acidic rocks: Cycle①changed upward from quartz-andesite, andesite, andesitic agglomeratic lava, andesitic agglomerate, andesitic breccia and andesitic breccia tuff, to sandy tuff, dacitic tuff lava. Cycle ② changed from basaltic andesite, basaltic agglomeratic lava to dacite, dacitic tuff lava, dacitic tuff. The upward vertical lithofacies succession of cycle ①is: lower subfacies of effusive facies, diatreme subfacies of volcanic conduit facies, airfall subfacies of explosive facies , reworked volcanogenic sediments sub-facies of volcanogenic sedimentary facies , pyroclastic flow subfacies of explosive face. The upward vertical lithofacies succession for cycle ②is: lower and upper subfacies of effusive facies, diatreme subfacies of volcanic conduit facies, lower subfacies of effusive facies, inner sufacies of intrusive facies, lower subfacies of effusive facies, pyroclastic flow subfacies of explosive facies, reworked volcanogenic sediment subfacies of volcanogenic sediment facies, lower subfacies of effusive facies. The lava in 3rd part of Yingcheng Formation erupted in the late period of fault subsidence and it is the important lithology record of the Songliao Basin’s transform from a fault subsidence basin to a sag basin.

The volcanic facies in study area include 12 subfacies in 5 volcanic facies. The porosity and permeabiltiy is better in upper sub-facies of effusive facies, inner subfacies of extrusive facies, cryptoexplosive breccias subfacies of volcanic conduit facies. Based on statistical results and the volcanic lithology and facies map, high cracks surface pore concentrates at diatreme subfacies and cryptoexploisve sub-facies of volcanic conduit facies, inner subfacies of extrusive facies, pyroclastic flow subfacies and base surge subfacies of explosive facies, lower subfacies of effusive facies which are close to the volcanic edifices center. Holes surface pore focus on upper and middle subfacies of effusive facies which locates in the edifice slope. Finally, according to the definition and category, the favorable reservoir is located at craters and mountain ridge of paleovolcano and surface pore data are outward reduced in zonal shape or one-side reduction.

Here reservoir geologic model refers to the spatial distribution characteristics of lithology, lithofacies and porosity & permeability for reservoir volcanic rocks. Field sections and two drilling wells are studied in detail here, reservoir units are divided and compared, and thus the volcanic reservoirs of the area are finally quantified and characterized. Volcanic facies sequence in the area under study is mainly effusive facies→ explosive facies→ effusive facies & extrusive facies→ volcanic sedimentary facies→ explosive facies→ volcanic conduit facies & effusive facies. Explosive facies and effusive facies are of the largest scales, with lateral ranging of some subfacies from 400 m to 4 000 m and thickness of a single layer ranging from 2 m to 130 m. Volcanic conduit facies, extrusive facies and volcanic sedimentary facies are smaller, lateral range is from 110 m to 1 500 m and thickness of single layer is from 3m to 85 m. According to volcanic reservoir classifying standards, the lower member of the Yingcheng Formation is the first and third grade, the 1st member is the first and second grade, with the fourth grade, the 2nd member is the first grade, and the 3rd member is interbedded by the first, second and third grades with thin layers of the fourth grade. The upper subfacies, volcanic neck subfacies and inner subfacies are the best volcanic reservoirs. The lower subfacies and hydrothermal breccias subfacies are better volcanic reservoirs, the explosive facies is middle, and the middle subfacies and volcanic sedimentary facies are bad volcanic reservoirs. Porosity and permeability of volcanic lavas would be slightly affected by their buried depth, while pyroclastic rocks would be getting worse with increasing buried depth. Volcanic rocks with low porosity and low permeability would be affected little by their buried depth.

It is known that the volcanic rocks of the Yingcheng Formation were altered into bentonite in the Songliao Basin, and the major bentonite deposits in the area are located in Jiutai City. These deposits are in unconformable contact with the underlying coal-bearing strata of the Shahezi Formation. Based on studying on the lithology of volcanic rocks, lithological sequence, microfeature and X-inflection, etc., bentonite in the area could be divided into the low-zeolite and high-zeolite types；pearilte, liparitic (vitreous) ash-latite with breccias and vitreous volcaniclastic rock serve as the major mineralized rocks；The fluids and their passageways were the major factors that determined if alteration happened. With increased alteration from the mineralized rocks into bentonite, their alteration of the rocks became more intensive, and hardness more weak, color more white and gradually disappearing of the lithofabric features; The thickness and continuity of the orebodies are strongly affected by volcanic facies. Generally, the best zones of bentonite are inner subfacies and middle subfacies of extrusive facies and air-fall subfacies and thermo-offal fluid subfacies of explosive facies. Besides, the erupted facies of vitreous liparite also makes up a major zone for the bentonite.

The diagenesis of volcanic rocks in Yingcheng Formation was classified as the early diagenesis and late diagenesis based on the observation of outcrop, well core, thin section and the analysis with scanning electric microscope. The early diagenesis includes corrosion, vaporization of volatile matter, isovolumetric condensing crystallization, pene-contemporaneous hydrothermal precipitation and crystallization, fusion, condensing constriction, differentiation condensing crystallization and the early impaction-cementation. The late diagenesis includes filling, devitrification, metasomatism, mechanical impaction and pressure solution, cementation and dissolution. The early diagenesis mainly influences the development of primary pore and the late diagenesis mainly influences the development of secondary pores. The pene-contemporaneous hydrothermal precipitation and crystallization, the early impaction-cementation, the filling, the mechanical impaction and pressure solution and cementation will harm the porosity and permeability of volcanic reservoir. The porosity and permeability will be improved after the vaporization of volatile matter, the isovolumetric condensing crystallization, the condensing constriction and dissolution.

The subaerial and subaqueous volcanic rocks have significant differences in lithology, texture and structure, alteration, occurence, contact with underlying strata, pore and fissure development. Subaerial volcanic rocks mainly comprise lavas, clastic lava, pyroclastic rocks and sedimentary pyroclastic rocks. Subaerial lava has rhyolitic structure. Bedding structure and few reverse hummocky structure formed in pyroclastic rocks. The subaerial volcanic rocks underwent weak alteration and unconformity with underling strata. Ancient weathering crusts and continental plant can be found. Main reservoir spaces in subaerial volcanic rocks are primary pore, condensing shrinkage joint, secondary dissolution pore, cleavage fissure in mineral and structural fracture. Subaqueous volcanic rocks mainly comprise glassy lava, crystal-vitric bedded/sedimentary tuff, bentonite/illite/montmorillonite/zeolite. Subaqueous volcanic rocks have pillow or orbicular structure, horizontal bedding, graded bedding, strong alteration. Subaqueous lava appears domed, lenticular shape, tuff appears stratiform shape, bentonite/illite/montmorillonite/zeolite near crater appears loose conglomeration with volcanic bombs. Contact relation of subaqueous volcanic rocks and underlying strata is conformity, disconformity or erosion. Main reservoir spaces of subaqueous volcanic rocks are primary pore, dissolution holes in amygdaloid body, explosive fracture, intergranular pores, erosion pore and fracture in matrix and phenocrysts and structural fracture. Both subaerial and subaqueous volcanic rocks can be found in Yingcheng Formation of Songliao Basin. Typical characteristics of subaerial volcanic rocks include rhyolitic structure, columnar joint, carbonized wood/silicified wood, angular unconformity contact with underlying strata. Typical features of subaqueous volcanic rocks include perlite with glassy structure and pillow structure, lamellar tuff, bentonite. Most of volcanic reservoirs in Yingcheng Formation of Songliao Basin are subaerial volcanic reservoirs. The inner subfacies of extrusive facies of subaqueous volcanic rocks are good reservoirs.

Large scale planar geological mapping, profiling survey and microfabric analyses proved that lithophysa structure was developed in rhyolite in Yingcheng coal mine area, Jiutai City. According to the genesis, occurrence,macro shape and microscopical characteristics，lithophysa was divided into three types：the independent lithophysa in bentonite，surface mounted lithophysa on stratiform rhyolite and interior lithophysa in the massive rhyolite．The diameter range of independent lithophysa is from a few centimeters to tens centimeters. Independent lithophysa is grape-like. Independent lithophysa distributed within the bentonite which altered from perlite. The crystallization differentiation of spheres which were formed by magma quenching into water generated the independent lithophysa. The diameter range of surface mounted lithophysa is from a few millimeters to a few centimeters. Surface mounted lithophysa is grape-like too. The surface mounted lithophysa distributed around the outer layer of the independent lithophysa in plane. Genesis mechanism of surface mounted lithophysa is the same as independent lithophysa. The diameter range of interior lithophysa is from a few millimeters to a few centimeters. Multi-rings structure was developed in the interior lithophysa. The mineral crystallization fractionation of gas-enriched magma from surface to inner releasing gas generated the interior lithophysa. These three types of lithophysa distribute in upper subfacies of effusive facies. The forming condition is condensing shrinkage in fixed volume.

3D modeling has been a key problem in the study of the volcanic rock reservoir in the northern part of the Songliao Basin. Take the Shengping area of the Songliao Basin as a target area, and select Petrel software and use data of tectonic interfaces and faults, the authors firstly establish the structure and the fault model of the area; secondly, by combination of certainty modeling and stochastic modeling methods, and by unite of both structural and fault models, the authors depict typical volcanic-rock characteristics and the changing law of lithofacies in three-dimensional space in detail to carry out the dynamic expression and display of volcanic reservoirs of the complex tectonics target zone by 3D visualization. The three dimensional structural model reveals that the northwest and the south of the study area are lack of the strata of the Yingcheng Formation and there is a dome structure with two structural highs in the area. The dome is closed at -2 810 m isopach, with an area of 32.45 km².The structural high is at -2 660.5 m level，and is of an amplitude of 150.5 m. Most of faults are oriented in N-S direction and are 2-5 km long，with a displacing distance of 8-30 m.

Most of the oil found up to now belong to light oil bed in Beier depression of Hailaer Basin. The fresh light oil-bearing core sections of sandstones show light colour, strong odour, yellowish fluorescence. But the colour, odour and fluorescence will lost after exposed sometimes. The density range of light oil is 0.79-0.82 g/cm³. The range of viscosity is 1.60-5.40 mPa·s. Max value of total hydrocarbon is more than 0.50%, and the ratio is more than 3.0. Total pyrolysis hydrocarbon is more than 2.00 mg/g. The ratio of lighter hydrocarbon to heavier hydrocarbon is from 2 to 6. Gas chromatography of light oil shows the range of carbon number is from nC₈ to nC₂₅ and the main peak carbon is nC₁₈-nC₂₀. The chromatography changes into line after oil exposed sometimes. Oil bed, oil-water bed and water bed were identified by using crossplot of specific oil content versus effective porosity. Standard and crossplot of oil type differentiation were formed base on regression analysis among index of PS, density and viscosity. The light oil bed and heavy oil bed were differentiated according to this standard. High productivity oil bed, industry oil bed, low production oil bed and dry bed were identified according to static productivity index and dynamic productivity index. The prediction accuracy was more than 90% with this method.