Changling Fault Depression Research Articles

Micro–Nano 3D CT Scanning to Assess the Impact of Microparameters of Volcanic Reservoirs on Gas Migration

Volcanic rock reservoirs for oil and gas are known worldwide for their considerable heterogeneity. Micropores and fractures play vital roles in the storage and transportation of natural gas. Samples from volcanic reservoirs in Songliao Basin, CS1 and W21, belonging to the Changling fault depression and the Wangfu fault depression, respectively, have similar lithology. This study employs micro–nano CT scanning technology to systematically identify the key parameters and transport capacities of natural gas within volcanic reservoirs. Using Avizo 2020.1software, a 3D digital representation of rock core was reconstructed to model pore distribution, connectivity, pore–throat networks, and fractures. These models are then analyzed to evaluate pore/throat structures and fractures alongside microscopic parameters. The relationship between micropore–throat structure parameters and permeability was investigated by microscale gas flow simulations and Pearson correlation analyses. The results showed that the CS1 sample significantly exceeded the W21 sample in terms of pore connectivity and permeability, with connected pore volume, throat count, and specific surface area being more than double that of the W21 sample. Pore–throat parameters are decisive for natural gas storage and transport. Additionally, based on seepage simulation and the pore–throat model, the specific influence of pore–throat structure parameters on permeability in volcanic reservoirs was quantified. In areas with well–developed fractures, gas seepage pathways mainly follow fractures, significantly improving gas flow efficiency. In areas with fewer fractures, throat radius has the most significant impact on permeability, followed by pore radius and throat length.

Subaqueous volcanic eruptive facies, facies model and its reservoir significance in a continental lacustrine basin: A case from the Cretaceous in Chaganhua area of southern Songliao Basin, NE China

The conventional lithofacies and facies model of subaerial and marine pyroclastic rocks cannot reflect the characteristics of subaqueous volcanic edifice in lacustrine basins. In order to solve this problem, the lithofacies of subaqueous eruptive pyroclastic rocks is discussed and the facies model is established by taking the tuff cone of Cretaceous Huoshiling Formation in the Chaganhua area of the Changling fault depression, Songliao Basin as the research object. The results indicate that the subaqueous eruptive pyroclastic rocks in the Songliao Basin can be divided into two facies and four subfacies. The two facies are the subaqueous explosive facies and the volcanic sedimentary facies that is formed during the eruption interval. The subaqueous explosive facies can be further divided into three subfacies: gas-supported hot pyroclastic flow subfacies, water-laid density current subfacies and subaqueous fallout subfacies. The volcanic sedimentary facies consists of pyroclastic sedimentary rocks containing terrigenous clast subfacies. A typical facies model of the tuff cone that is formed by subaqueous eruptions in the Songliao Basin was established. The tuff cone is generally composed of multiple subaqueous eruption depositional units and can be divided into two facies associations: near-source facies association and far-source facies association. The complete vertical succession of one depositional unit of the near-source facies association is composed of pyroclastic sedimentary rocks containing terrigenous clast subfacies, gas-supported hot pyroclastic flow subfacies, water-laid density current subfacies and subaqueous fallout subfacies from bottom to top. The depositional unit of the far-source facies association is dominated by the subaqueous fallout subfacies and contains several thin interlayered deposits of the water-laid density current subfacies. The gas-supported hot pyroclastic flow subfacies and the pyroclastic sedimentary rocks containing terrigenous clast subfacies are favorable subaqueous eruptive facies for reservoirs in continental lacustrine basins.

Reservoir Characteristics and Development Model of Subaqueous Pyroclastic Rocks in a Continental Lacustrine Basin: A Case Study of the Chaganhua Subsag in the Changling Fault Depression, Songliao Basin

Industrial oil and gas eruptions underwater have been found in the pyroclastic rocks of the Huoshiling Formation in the continental lacustrine basin of the Changling fault depression, Songliao Basin. This paper investigates the reservoir space characteristics, physical characteristics, and pore structure differences of subaqueous pyroclastic reservoirs in the Huoshiling Formation, and the causes of physical property differences of different types of reservoirs and their formation and evolution processes are analyzed. (1) The content of volcanic glass in tuff is higher, the reservoir space is dominated by devitrification pores and dissolution pores, and the coarser the grain size, the more favorable the physical properties, with larger pore sizes and higher porosities. The content of clay minerals in sedimentary tuff is high, the pores between clay minerals are the main pores, and the physical properties of sedimentary tuff are poor. The content of soluble components such as feldspar, debris, and laumontite is high in tuffaceous sandstone, which is dominated by dissolution pores. (2) Primary pores are not developed in the pyroclastic reservoirs in the study area, and the reservoirs are relatively dense, with an average porosity of 2.43% and an average permeability of 0.076 mD. The coarse-grained tuff has the highest porosity, followed by tuffaceous sandstone and fine-grained tuff, and the sedimentary tuff has the least favorable physical properties. (3) Devitrification was an important cause of the high-porosity and ultralow permeability of tuff reservoirs. Two oil and gas charges in the middle diagenetic stage led to the organic acid dissolution of rocks. In addition, fractures can provide migration channels for organic acids and deep hydrothermal fluids, leading to late dissolution, and can connect various scattered dissolution pores to improve the effectiveness of the reservoir space. (4) Coarse-grained tuff reservoirs that developed in the proximal facies are favorable targets for hydrocarbon exploration.

Evolutionary characteristics and key controlling factors of the volcanic rocks in the Lower Cretaceous Changling fault depression, Songliao Basin, China

The Songliao Basin is a large petroliferous basin located in Northeast Asia; the complex structure and volcanic filling are obstructions to the petroleum geological exploration of the Lower Cretaceous strata in the basin. Based on seismic, logging and lithologic data, this paper reveals the tectonic–stratigraphic characteristics of the Changling fault depression in the Songliao Basin, identifies the depression's volcanic rocks and summarizes their distribution patterns and changes, and finally analyzes the main factors controlling volcanic rock development combined with the regional tectonic background. The research shows the fault extension and subsidence caused the Changling fault depression to gradually evolve from an independent fault depression group to a connected large lake basin. The volcanic rocks in the fault depression are mainly “sill–like” volcanic lava and mounded volcaniclastic rocks, and their development can be divided into several stages. In the early Valanginian to Barremian, volcanic rocks show a large range of contiguous bedded and buninoid-structured rocks, which separate several small sedimentary sags; during the early Barremian to the late Aptian, volcanic rocks stopped developing; from the late Aptian to the late Albian, the volcanic rocks in the basin underwent multiple evolutionary periods, and their morphology gradually changed from mats and gentle mounds to high-angle cones and domes. Mantle upwelling caused by plate activity in Northeast Asia is the main driving force of extension and volcanic eruptions in the Songliao Basin, and the deep basement faults that formed by extensional activity control the magma upwelling channel, thus affecting the active periods, scale, morphology and distribution characteristics of volcanic rocks.

Possible geological interpretation of the volcanic seismic facies based on volcanostratigraphy elements: A case analysis of the Yingcheng Formation in the Changling Fault Depression, Songliao Basin, NE China

Volcanic rocks in faulted depressions are one of the most interested areas for hydrocarbon exploration. In a frontier basin exploration, integrated interpretation of the seismic facies of volcanic rocks is a key success. The key information of boundary system and deposited unit in the volcanostratigraphy did not attract sufficient attention during the process of seismic stratigraphic interpretation of volcanic rocks. In this paper, the volcanic rocks of the Yingcheng Formation in the Changling Fault Depression of the Songliao Basin are taken as an example. According to the maximum average slope, the volcanic seismic facies were divided into three types: mounded seismic facies unit (MSFU), tabular seismic facies unit (TSFU), and mounded-tabular seismic facies unit (M-TSFU). MSFU consists of lava dome and simple lava flows, which has fewer reservoir layers, medium to poor reservoir quality with limited extension. The TSFU comprises more complex component of simple lava flow and base surges, and contains more layers, with good-medium reservoir quality and a large reservoir extension. The M-TSFU has numerous reservoir layers with good reservoir quality and a significant reservoir extension, as well as a higher proportion of braided lava flows and pyroclastic flows. Going from the most favorable reservoir targets to the least favorable, the following units were deposited in the Changling Fault Depression: pyroclastic flow, braided lava flow, base surge, simple lava flow, lava dome, and reworked volcanic clastic flow. The study suggested that mounded-tabular facies units are potential favorable exploration targets in the Songliao Basin. This paper provides a technical route for seismic facies interpretation of volcanic rocks and the analysis of favorable volcanic exploration targets in faulted volcanic basins.

CT-based 3D pore-fracture network analysis of volcanic reservoirs of Lower Cretaceous Yingcheng formation in southern Songliao Basin, China: Impact on natural gas migration

Volcanic rocks as an important part of basins are found in almost all basins in the world. Although volcanic rock reservoirs are denser and more heterogeneous than conventional reservoirs, they still have good storage capacity in the deeper hydrocarbon-bearing basins. Due to the presence of a large number of irregular and random pores, throats and fractures in volcanic reservoirs at micron-nano scale, its permeability and reservoir capacity are complex. A series of experiments show an abnormal negative correlation between porosity, permeability and natural gas diffusion coefficient in volcanic reservoir rocks of the Yingcheng Formation in the southern Songliao Basin. The dacite sample from CS105 well in Changling Fault Depression and the andesite sample from DS9 well in Dehui Fault Depression with this negative correlation phenomenon were selected, the micron-nano CT scanning technology and Avizo software are applied to quantitively evaluate the 3D pore-fracture network system of the volcanic reservoir samples at multiscale. By comparing the statistical results from CT scanning of the two samples, the dacite sample of CS105 well with higher diffusion coefficient has higher porosity, more connected pores, larger average pore volume and higher average coordination numbers, in addition, the micro-fractures in the CS105 sample promotes the development of secondary pore-throats through later dissolution and further improve the physical properties of volcanic rock reservoirs. In the meantime, the gas seepage simulation results also prove the positive correlation between porosity, permeability and diffusion coefficient of volcanic rock reservoir. The micron-nano CT scanning can more accurately evaluate the physical properties of volcanic rock reservoirs with a large number of pore-throats and fractures at the micron-nano scale, providing theoretical basis for the study of natural gas migration mechanism in highly heterogeneous tight volcanic rock reservoirs.

Effect of Authigenic Chlorite on the Pore Structure of Tight Clastic Reservoir in Songliao Basin.

Authigenic chlorite is a common clay mineral in clastic rock reservoirs, and it has an important influence on the pore structure of tight clastic rock reservoirs. In this paper, the tight clastic reservoirs in the Lower Cretaceous Yingcheng Formation in the Longfengshan subsag in the Changling fault depression in the Songliao Basin were investigated. Polarized light microscopy, scanning electron microscopy (SEM), X-ray diffraction (XRD), high-pressure mercury injection (HPMI), and low temperature nitrogen adsorption (LTNA) were used to study the influence of authigenic chlorite on the pore structure of tight clastic reservoirs. The results show that the authigenic chlorite in the study area was mainly generated in the form of pore linings. The formation of the authigenic chlorite was mainly controlled by the parent rock type and the sedimentary microfacies in the provenance area. The hydrolysis and dissolution of the iron- and magnesium-rich intermediate-mafic magmatic rocks and the high-energy, open, weakly alkaline reducing environment in the delta-front underwater distributary channel were the key factors controlling the formation of the authigenic chlorite in the study area. The pore-lining chlorite slowed down compaction and inhibited quartz overgrowth, protecting the original pores. Moreover, there are a large number of intercrystalline pores in the chlorite, which provided channels for the flow of acidic water and thus the formation of secondary pores, playing a positive role in the physical properties of the tight clastic rock reservoirs. However, the pore-filling chlorite also blocked the pore throats, playing a negative role in the physical properties of the tight clastic rock reservoirs. The tight clastic rock reservoirs with pore-lining chlorite generally had low displacement pressures and large pore throat radii. The morphology of the nano-scale pores was mainly parallel plate-shaped slit pores. There were many primary pores and a small number of secondary pores in the reservoir. Some of the pores were connected by narrow-necked or curved sheet-like throats, and the pore structure was relatively good. A higher relative content of chlorite led to a larger nano-scale pore throat radius, a smaller specific surface area, a smoother pore surface, and stronger homogeneity. Authigenic chlorite played a positive role in the formation of the tight clastic reservoirs in the study area.

Seismic interpretation and geological evaluation of hydrocarbon source rocks in volcanic-rich continental lacustrine rift basins: A case study of the Lower Cretaceous Yingcheng Formation from the Changling Fault Depression in the Songliao Basin, NE China

The Lower Cretaceous Yingcheng Formation in the Changling Fault Depression in the Songliao Basin is composed of volcanic-rich continental lacustrine rift basin sediments. Its complex stratigraphic structure and the difficulty in predicting the hydrocarbon source rock distribution restrict the exploration and evaluation of deep hydrocarbons in this region. This paper uses seismic stratigraphy to divide the strata and interpret dark mudstone layers based on logging and seismic. These data are combined with geochemical test data from hydrocarbon source rocks to assess its quality and predict its distribution. This study indicates that the three types of unconformities identified divide the Yingcheng Formation into four sedimentary sequences. In the Yingcheng Formation depositional period, the number of grabens or half-grabens associated with the Changling Fault Depression decreased, the size of the rift basins increased, and the depositional center migrated to the north and west. During the depositional period of the First and Second Members, volcanic rocks were widely developed, and mud sediments were deposited between several small grabens or half-grabens. During the depositional period of the Third and fourth Members, the study area became a unified lacustrine rift basin with clearly defined geological signatures developed in each sedimentary sequence, which can be divided into three systems tracts. Mudstones in the Lake Transgressive Systems Tract are laterally continuous and widely distributed. The organic matter in these mudstones, with fair to good abundance levels, is predominantly type II2 and type III kerogen and all have reached mature to highly mature stage of thermal evolution, which are favorable hydrocarbon source rock layers. In plan view, the favorable hydrocarbon source rock zones are mostly formed in the Changling Sag, Dongling Structural Zone and Longfengshan Sag. This study offers guidance and direction for deep hydrocarbon exploration in the Changling Fault Depression, and also provides a reference for methods and ideas to predict hydrocarbon source rock distribution in other lacustrine rift basins.

Study on the pore structure and fractal characteristics on shale rock and isolated organic matter in lacustrine shales from the Changling fault depression in the Songliao Basin, China

The stock of shale gas in the Shahezi shale reservoir in the Changling fault depression, Songliao Basin, is believed to be worth exploring. In-depth study on the pore structure and fractal characterization of organic matter (OM) can help better understand the pore system of shale reservoir, which has implications for the exploration of lacustrine shale. To demonstrate the nanoscale pore structure and irregularity of the isolated OM, we collected a large number of samples and then conducted a series of laboratory experiments, such as X-ray diffraction, scanning electron microscopy, and [Formula: see text] and [Formula: see text] adsorption experiments to determine the pore structure parameters and reveal their heterogeneity according to Frenkel-Halsey-Hill theory. As suggested by the experimental results, the pore size distribution curve of the [Formula: see text] and [Formula: see text] exhibits similar pore peaks, whereas the trends of change in bulk shale and isolated OM samples are basically paralleled. The pore volume of the isolated OM ranges between 0.034 and [Formula: see text], which is approximately 0.90–3.06 times that of bulk shale samples. As for the fractal dimensions [Formula: see text] (2.594 on average) and [Formula: see text] (2.657 on average) of bulk shale, they are larger as compared with isolated OM, indicating that inorganic minerals can make a significant difference in the heterogeneity of shale pores. The fractal dimensions ([Formula: see text] and [Formula: see text]) of bulk shales indicate a close correlation with the parameters of pore structure, whereas there is no significant correlation observed between the dimensions of isolated OM and its parameters. In addition, thermal maturity and solid bitumen have only limited impact on the OM pore structure of isolated OM samples. Then, we conducted further research to reveal that the insoluble OM macerals derived from terrestrial higher plants can be used to explain the difference in pore structure and heterogeneity between isolated OM samples. Therefore, we arrived at the conclusion that the composition of macerals depends on the exact pore structure and fractal characteristics of isolated OM samples with similarity in thermal maturity.

Spatial Characteristics and Genesis of Tight Clastic Reservoirs in Yingcheng Formation of Changling Fault Depression in the Southern Songliao Basin

Tight oil and gas has become a hot spot for unconventional oil and gas exploration. How to find high-quality reservoirs under the conditions of low porosity and permeability has become a key issue restricting tight oil and gas exploration. This paper takes the deep-seated tight clastic rocks in the Changling fault depression in the Songliao Basin as the research object and comprehensively applies various technologies and methods such as microscopic observation, temperature measurement of inclusions and paleopressure recovery, and water-rock simulation experiments, to summarize the storage of tight reservoirs. Set space types and analyze their formation mechanism. The research results show that (1) the tight clastic reservoir space types of Yingcheng Formation in the Longfengshan subsag of the Changling fault depression in the southern Songliao Basin include residual primary pores, secondary dissolved pores, and microfractures, with mainly secondary dissolved pores; (2) pore lining chlorite is an important mechanism for the preservation of primary pores; (3) water-rock simulation experiments have confirmed that volcanic rock cuttings are easy to dissolve and are the main contributor to the secondary dissolution pores in the study area; and (4) the Raman displacement technique of methane inclusions has confirmed the existence of overpressure, which is the cause of hydrocarbon generation and pressurization and is the main motivation for a microcrack formation.

Determination of Favorable Lithofacies for Continental Shale Gas: A Case Study of the Shahezi Formation, Changling Fault Depression, Songliao Basin

In order to determine the optimum lithofacies for continental shale, the reservoir characteristics of different lithofacies types were studied based on a series of experiments. The lacustrine organic-rich shale of the Shahezi Formation is divided into siliceous (ORS), argillaceous (ORA), calcareous (ORC), and mixed (ORM) shales. The ORS, ORA, ORC, and ORM shales all carried out comprehensive reservoir comparative analysis. The results showed that the moderate content of clay minerals (45%) can significantly improve porosity, and high and low clay mineral contents are not conducive to the improvement of porosity. The ORM shale tends to have better pore connectivity than the ORS and ORA shales, and the ORC shale has the poorest pore-throat connectivity in micron-size. Internal pores in bitumen and clay shrinkage cracks are the dominant pore type and are well developed in ORS and ORM shales. The two types of pores are less developed in the ORA shale; however, dissolution pores are better developed than those of ORS and ORM shales. Inorganic pores are well-developed in the ORC shale, but organic pores are not. Organic and inorganic pores tend to be better connected in the ORM shale than those of the other three types, which could help improve the gas storage capacity. The ORM shale may have more irregular surfaces and lower liquid/gas surface tension. The higher capillary condensation on pore surfaces is more likely to occur in the ORA shale. The ORS shale offers fewer adsorption sites for CH4 and has lower adsorption capacity. The ORC shale has weak heterogeneity of the pore structure. Therefore, the ORM shale may be the most favorable lithofacies for shale gas enrichment and development, which has high porosity, good pore connectivity, moderate brittleness, and strong gas adsorption and storage capacity, followed by the ORS and ORA shales. The ORC shale is the worst.

Possible Geological Interpretation of the Volcanic Seismic Facies Based on Volcanostratigraphic Elements: A Case Analysis of the Yingcheng Formation in the Changling Fault Depression, Songliao Basin, Ne China

Possible Geological Interpretation of the Volcanic Seismic Facies Based on Volcanostratigraphic Elements: A Case Analysis of the Yingcheng Formation in the Changling Fault Depression, Songliao Basin, Ne China

Organic pore heterogeneity and its formation mechanisms: Insights from the Lower Cretaceous lacustrine Shahezi shale in the Songliao Basin, NE China

Pores associated with organic matter are well known to play a significant role in shale gas capacities. However, an extremely high heterogeneity of organic pores often impacts our evaluation of reservoir quality. In this work, we analyze the formation mechanisms of the heterogeneity based on positioning observation method using a combination of field emission scanning electron microscopy and optical microscopy. These analyses were conducted on six lacustrine shale samples at the gas window in the Lower Cretaceous Shahezi shale, which is located in the Changling Fault Depression of Songliao Basin. The results reveal that organic pore heterogeneity is mainly attributed to four controlling factors. (a) One is different hydrocarbon generation potentials among different macerals. The degree of pore development from high to low is solid bitumen, vitrinite, and inertinite. The content of carbon by the weight percentage of solid bitumen, vitrinite, and inertinite is in the opposite order, which reflects that the different hydrocarbon generation potential of each maceral is the dominant factor. (b) Another one is the remnants of primary pores in organic matter with plant cell structures. Well preserved telinite, fusinite, and semi-fusinite show cell structures, and the cells that are not completely compressed or not fully filled retain the original residual pores. (c) The third one is evolutional differences of individual solid bitumen. Not all solid bitumen developed organic pores, which is mainly attributed to the difference of solid bitumen reflectance in different solid bitumen particles. The solid bitumen reflectance of porous solid bitumen is mostly distributed between 1.6% and 2.0%, in which oil cracking to gas is dominant and porous residual solid bitumen subsequently forms. The solid bitumen reflectance of non-porous solid bitumen peaks in 1.2–1.6%, which is in the stage of kerogen transformation and oil generation with rare pore development. (d) The last one is the catalysis of clay minerals. All organoclay complexes develop abundant sponge-like pores due to catalysis during the transformation from smectite to illite. A high content of illite in the mixed layers I/S increases the specific catalytic activities, promoting the organic matter and solid bitumen to further generate hydrocarbon and form pores. Most organic–inorganic mixtures develop pores also because of catalysis from inorganic minerals.

Fractal Characterization of Nanoscale Pores of Volcanic Reservoirs in the Dongling Area, Changling Fault Depression, Songliao Basin

Fractal theory is an efficient method to characterize quantitatively tight rocks. Volcanic rocks are very promising reservoirs, and their pore structures have considerable influence on the occurrence and percolation mechanisms of oil and gas. Therefore, the research topics of pore structure and fractal characteristics are important for sustainable volcanic resource development. The pore structure and fractal characteristics of microscopic pores of volcanic reservoirs in the Changling Fault Depression, Songliao Basin, were studied by combining fractal theory with mercury intrusion porosimetry and low-temperature nitrogen adsorption technique. After quantitative characterization of the nanoscale pore size distribution (PSD), four fractal dimensions were calculated. Subsequently, the relationships between fractal dimensions and pore structure parameters were evaluated. Three types of PSD models of volcanic reservoirs in the study area were established. The relationships between fractal dimensions and PSD models, as well as the clustering characteristics of the fractal dimensions, were investigated. The study revealed that the volcanic reservoirs developed a certain proportion of nanoscale pores with morphological characteristics dominated by wedge-shaped pores and slit pores. D4 is relatively strongly negatively correlated with pore size, illustrating that it can better reflect pore structure compared to the other fractal dimensions. Additionally, D4 can reflect pore surface roughness. This study shows that D1 and D2 can distinguish PSD models well, but D3 and D4 are more effective for the identification of the Type II PSD model. The fractal dimensions were divided into four clusters via hierarchical cluster analysis, each corresponding well to a certain PSD model or PSD model combination.

Quantitative Characterization of Organic Pore Structure from Gas Adsorption in Lower Cretaceous Lacustrine Shales in the Songliao Basin, NE China

Abstract Organic matter (OM) pores are widely considered to be important for gas storage and transportation. In this work, we quantitatively analyze the pore structure of OM and its controlling factors through geochemical and petrologic analyses, optical microscope, OM isolation, and adsorption isotherms. These analyses were carried out on lacustrine shale samples from the Lower Cretaceous Shahezi Formation, which is located in the Changling Fault Depression in Songliao Basin. The results show that the content of soluble OM (SOM) is low, accounting for 0.26%-3.75% of total OM. The contribution of pore development from SOM itself is limited. After extraction of SOM by chloroform, pore volume (PV), specific surface area (SSA), and average pore diameter (APD) exposed to gas molecules greatly increase. The existence of SOM has an obvious effect on pores of >10 nm, especially the clay mineral-related pores that contribute the most to the total PV. The content of kerogen is higher than SOM and accounts for 9.9%-65.5% (averaging 24.0%) of total PV in bulk shale, only second to minerals. More importantly, kerogen is the dominant contributor to organic PV, accounting for 95.8%-99.7% (averaging 98.3%) of the total organic PV. The pores developed in the kerogen peak at 0.4-0.7 nm and 10-30 nm. The solid bitumen (SB) followed by vitrinite and inertinite in kerogen contributes the most to the total kerogen PV.

Quantitative characteristics of nanoscale pores in mafic-intermediate volcanic rock reservoirs in the Changling fault depression, Songliao Basin

Tight volcanic reservoirs can have porosities of 2–8%, and the pore space primarily consists of nanoscale pores. Thin section observations, scanning electron microscopy (SEM), mercury intrusion porosimetry (MIP), and low-temperature nitrogen adsorption (LTNA) were used to qualitatively and quantitatively characterize the nanoscale pore size distribution (PSD). The MIP results show that the nanoscale pore diameters in the mafic-intermediate volcanic rocks mainly range from 4 to 100 nm. Moreover, different lithologies have different PSD characteristics. The LTNA results indicate that the nanoscale pore morphologies are mainly the narrow slit type and irregular type. Our results suggest that nanoscale pores are favorable for gas accumulation. Methane adsorption theory indicates that the lower pore diameter limit for methane adsorption is 18.5 nm and the lower filling porosity limit in the volcanic rock reservoir is 2.80%. Based on the PSD and gas testing results, a model of nanoscale pores’ PSD and gas-bearing properties is established.

Volcanism from different eruption cycles during the Early Cretaceous in the Changling fault depression of the songliao basin, NE China, and their implications for timing of lithospheric thinning

ABSTRACT Late Mesozoic lithospheric extension in NE China resulted in the development of a large extensional province and widespread formation of volcanic-sedimentary basins. The Songliao Basin is the largest one and contains voluminous volcanic rocks composing the majority of the basin fill. This study focuses on two adjacent eruption cycles, the Huoshiling Formation (K1h) and the first member of the Yingcheng Formation (K1yc1), in the Changling fault depression of the Songliao basin, constrains their time ranges and compares the origins of volcanic rocks. Zircon populations from K1h yield U-Pb ages of 124–118 Ma; those from K1yc1 yield younger ones (115–106 Ma). Different volcanic rocks are identified in K1h (alkaline basic rocks, calc-alkaline intermediate-acid rocks) and K1yc1 (alkaline basic rocks, A-type rhyolites), and their geochemistry and isotope characteristics confirm their different origins. The alkaline basic rocks from K1h have the similar magma source as those from K1yc1; both formed under within-plate conditions from an ocean island basalt (OIB)-type mantle source, assumed to be the heterogeneous shallow asthenosphere. The calc-alkaline intermediate-acid volcanic rocks from K1h formed by fractional crystallization of magma, related to the enriched lithospheric mantle, whereas the A-type rhyolites from K1yc1 directly originated from the partial melting of crust newly formed from the depleted mantle. The development of alkaline basic rocks and A-type acid rocks, a typical bimodal volcanic assemblage in K1yc1, requires a relatively thin lithosphere and thus implies that lithospheric thinning reached its maximum during this time (115–106 Ma). However, the rare expression of alkaline basic rocks and the formation of acid rocks mainly by fractional crystallization in K1h indicate that the lithosphere was relatively thick; during this time (124–118 Ma), the lithosphere below the Songliao Basin had just begun thinning. These different stages of lithospheric extension may be due to the intermittent rollback of the Palaeo-Pacific Plate.

Coupling relationship between reservoir diagenesis and hydrocarbon accumulation in Lower Cretaceous Yingcheng Formation of Dongling, Changling fault depression, Songliao Basin, Northeast China

ABSTRACT The Lower Cretaceous Yingcheng Formation in the southern Songliao Basin is the typical tight oil sandstone in China. In order to better predict the petrophysical properties of the tight sandstone reservoirs in the Lower Cretaceous Yingcheng Formation, Songliao Basin, Northeast China, the diagenesis and porosity evolution was investigated using a suite of petrographic and geochemical techniques including thin section analysis, scanning electron microscopy, mercury intrusion and fluid inclusion analysis, on a set of selected tight sandstone samples. Combined with the histories of burial evolution, organic matter thermal evolution and hydrocarbon charge, the matching relationship between reservoir porosity evolution and hydrocarbon accumulation history is analyzed. The result showed that the tight sandstone reservoirs characterized of being controlled by deposition, predominated by compaction, improved by dissolution and enhanced by cementation. The hydrocarbon accumulation period was investigated using a suite of hydrocarbon generation and expulsion history, microfluorescence determination and temperature measurement technology. According to the homogenization temperature of the inclusions and the history of burial evolution, Yingcheng Formation has mainly two phases hydrocarbon accumulation. The first phase of oil and gas is charged before the reservoir is tightened, the oil and gas generated by Shahezi source rocks enter the sand body of Yingcheng Formation, influenced by the carrying capability of sand conducting layer, oil and gas is mainly conducted by the better properties and higher connectivity sand body and enriched in the east, which belongs to the type of densification after hydrocarbon accumulation. The second phase of oil and gas charge after densification, which belongs to the type of densification before the hydrocarbon accumulation.

Pore Connectivity Characterization of Lacustrine Shales in Changling Fault Depression, Songliao Basin, China: Insights into the Effects of Mineral Compositions on Connected Pores

Pore connectivity of lacustrine shales was inadequately documented in previous papers. In this work, lacustrine shales from the lower Cretaceous Shahezi Formation in the Changling Fault Depression (CFD) were investigated using field emission scanning electron microscopy (FE-SEM), mercury intrusion capillary pressure (MICP), low pressure gas (CO2 and N2) sorption (LPGA) and spontaneous fluid imbibition (SFI) experiments. The results show that pores observed from FE-SEM images are primarily interparticle (interP) pores in clay minerals and organic matter (OM) pores. The dominant pore width obtained from LPGA and MICP data is in the range of 0.3–0.7 nm and 3–20 nm. The slopes of n-decane and deionized (DI) water SFI are in the range of 0.34–0.55 and 0.22–0.38, respectively, suggesting a mixed wetting nature and better-connected hydrophobic pores than hydrophilic pores in the Shahezi shales. Low pore connectivity is identified by the dominant nano-size pore widths (0.3–20 nm), low DI water SFI slopes (around 0.25), high geometric tortuosity (4.75–8.89) and effective tortuosity (1212–6122). Pore connectivity follows the order of calcareous shale > argillaceous shale > siliceous shale. The connected pores of Shahezi shales is mainly affected by the high abundance and coexistence of OM pores and clay, carbonate minerals host pores.

The Impacts of Matrix Compositions on Nanopore Structure and Fractal Characteristics of Lacustrine Shales from the Changling Fault Depression, Songliao Basin, China

The Lower Cretaceous Shahezi shales are the targets for lacustrine shale gas exploration in Changling Fault Depression (CFD), Southern Songliao Basin. In this study, the Shahezi shales were investigated to further understand the impacts of rock compositions, including organic matters and minerals on pore structure and fractal characteristics. An integrated experiment procedure, including total organic carbon (TOC) content, X-ray diffraction (XRD), field emission-scanning electron microscope (FE-SEM), low pressure nitrogen physisorption (LPNP), and mercury intrusion capillary pressure (MICP), was conducted. Seven lithofacies can be identified according to on a mineralogy-based classification scheme for shales. Inorganic mineral hosted pores are the most abundant pore type, while relatively few organic matter (OM) pores are observed in FE-SEM images of the Shahezi shales. Multimodal pore size distribution characteristics were shown in pore width ranges of 0.5–0.9 nm, 3–6 nm, and 10–40 nm. The primary controlling factors for pore structure in Shahezi shales are clay minerals rather than OM. Organic-medium mixed shale (OMMS) has the highest total pore volumes (0.0353 mL/g), followed by organic-rich mixed shale (ORMS) (0.02369 mL/g), while the organic-poor shale (OPS) has the lowest pore volumes of 0.0122 mL/g. Fractal dimensions D1 and D2 (at relative pressures of 0–0.5 and 0.5–1 of LPNP isotherms) were obtained using the Frenkel–Halsey–Hill (FHH) method, with D1 ranging from 2.0336 to 2.5957, and D2 between 2.5779 and 2.8821. Fractal dimensions are associated with specific lithofacies, because each lithofacies has a distinctive composition. Organic-medium argillaceous shale (OMAS), rich in clay, have comparatively high fractal dimension D1. In addition, organic-medium argillaceous shale (ORAS), rich in TOC, have comparatively high fractal dimension D2. OPS shale contains more siliceous and less TOC, with the lowest D1 and D2. Factor analysis indicates that clay contents is the most significant factor controlling the fractal dimensions of the lacustrine Shahezi shale.