Archive

2016, Volume 23 Issue 1
15 January 2016 Previous Issue    Next Issue
---
Article


For Selected:

Download Citations EndNote Ris BibTeX

Toggle Thumbnails

Article

Select

Controlling Factors on the Enrichment and High Productivity of Shale Gas in the WufengLongmaxi Formation, southeastern Sichuan Basin. 2016, 23(1): 1-10.  DOI: 10.13745/j.esf.2016.01.001 Abstract ( 3315 )   PDF (2016KB) ( 3968 )   Based on a comparison of geological and surface conditions for shale gas in China and America, we conclude that marine strata in South China having similar properties to those of America are targets for shale gas exploration, and the Sichuan Basin and its surroundings are favorable exploration areas. After six years of research and exploration, the Fuling Shale Gas field, which is the first major commercial shale gas play in China, was finally found in the Sichuan Basin in 2012 and then successfully developed. The shale gas enrichment and high productivity in the WufengLongmaxi Formation is mainly controlled by the original depositional environment which determines organic matter content and postdepositional conditions that promote shale preservation and gas retention within the shale after thermal maturation. Deposition and distribution of the shales are controlled by the platform depression environment. Thickness and TOC content are the evaluation parameters for play. The late preservation conditions control the enrichment of shale gas. There are favorable preservation conditions and high degree of shale gas enrichment in the internal of Sichuan Basin, which are characterized by widely distributed Triassic gypsolyte layers and high pressure coefficient. The areas where both original depositional environment and preservation conditions are favorable should be given priority in play evaluation. Comprehensive analysis of the shale gas reservoir indicates that organic matter content is the principal control on shale gas enrichment, the organic micropores are the main reservoir space, horizontal bedding fractures ensure horizontal seepage, and that the high siliceous mineral content ensures good fracturing effect, high pressure coefficient indicates high degree of shale gas enrichment. These five properties have genetic relationships and statistical correlation and are characterized by “five properties in one position” distribution features in vertical. The high quality shales with “five properties in one position” feature is conducive to the enrichment of shale gas and benefit for its development, which is the main development of shale gas layer and key objectives of horizontal well trajectory. Related Articles | Metrics

Select

Unique geologic features of burial and superimposition of the Lower Paleozoic shalegas across the Sichuan basin and its periphery. 2016, 23(1): 11-28.  DOI: 10.13745/j.esf.2016.01.002 Abstract ( 3188 )   PDF (3286KB) ( 4567 )   The Sichuan Basin locates at the transition zone between PaleoPacific Tectonic Domain and TethysHimalayan Tectonic Domain, of which the marine and marinetoterrestrial black shale has experienced substantial burial (high thermal maturation), significant uplift and erosion, and strong deformation from Mesozoic to Cenozoic. Apatite fissiontrack data, geophysics, sedimentary thickness and vitrinite reflectance etc., are used to decipher the geologic features of the burial and superimposition of the Lower Paleozoic shale gas across the Sichuan Basin and its peripheries in this paper, which highlights the characteristic difference to the shale (gas) in the U.S.A. It indicates about 10004000 m surface denudation across the Sichuan Basin since Late Cretaceous, based on about 100 modeled thermal histories from apatite fission track data. Different surface denudation and thickness of the terrestrial deposits played a firstorder influence on the Paleozoic depth. The bases of the Lower Silurian Longmaxi Formation and Lower Cambrian Niutitang Formation have depth more than 6 500 m and 9 000 m, respectively, of which the contour lines are characterized by NESW strike, and the depth decreases from NE to SW across the Sichuan Basin. The minimum paleodepth of the base of the Longmaxi Formation is ~6000 m in the Suijiang area, southern Sichuan Basin, and the maximum is ~9000 m in the northern Sichuan Basin. Furthermore, there are two areas, i.e. SuijiangYibinLuzhou area, and DazhouBazhong area, with NESW strike and smaller paleodepth of the base of the Longmaxi Formation, where the paleodepth increases southeastward and northward, respectively. The maximum paleodepth of the base of the Niutitang Formation is more than ~11000 m, in the western and northern Sichuan Basin, and the minimum paleodepth is less than ~8000 m, locating in the YibinZigongSuining area in the central and southern Sichuan Basin. The thermal maturation of the Longmanxi and Niutitang Formations are more than 2.4% and 2.8%, respectively, and it decreases from northeast to southwest across the Sichuan Basin and its peripheries. It indicates a close relationship between the thermal maturation of the Lower Paleozoic black shale and their paleodepth. Furthermore, the significant uplift, erosion, and strong deformation resulted in a dynamic stressstain state, changing temperature and pressure etc., and thus a dynamic reservation condition of the Lower Paleozoic shalegas. It should be noted that there was a correlation between the insitu success and setback of exploration in the Lower Paleozoic shalegas and their differential burial, uplift and denudation, and deformation across the Sichuan Basin and its peripheries, indicating a very important geologic feature of the burial and superimposition to the distribution of the Lower Paleozoic shalegas. Thus, not only should we pay more attention to what controls the highquality reservoir of shalegas, but also to what controls the highproductivity reservoir of shalegas under such a unique geologic feature in the South China. Related Articles | Metrics

Select

Discovery and characteristics of the Fuling shale gas field and its enlightenment and thinking. 2016, 23(1): 29-43.  DOI: 10.13745/j.esf.2016.01.003 Abstract ( 3402 )   PDF (3072KB) ( 4452 )   The Fuling shale gas field is located at the Jiaoshiba structure, eastern margin of the Sichuan Basin, which has proven geological reserves of 380.6 billion cubic meters. It is the first commercial shale gas field outside the North America. The Jiaoshiba structure is a rhomboid faulted anticline, which is controlled by the northeast and northsouth trending fault system, whose special structural settings play an important role in shale gas enrichment. The Fuling shale gas production layer is WufengLongmaxi shale, which is characterized by a large thickness of organicrich shale, high content of total organic matter (TOC), high degree of thermal maturity, high content of brittle minerals, overpressure, high initial production rates, welldeveloped natural fracture networks and alkane carbon isotopic reversal. After more than three years of development, it is confirmed that the Fuling shale gas field has abundant shale gas resource with stable production and high formation pressure. Through the analysis of regional geological features and comparison with gas fields in the U.S., the basic characteristics, enlightenment and thinking of shale gas in Fuling are summarized and put forward. Firstly, there are high production and enrichment of shale gas fields in China; but the controlling factors are different from the gas fields in the U.S. Forward structure and advanced regional strikeslip effect are extremely important. Secondly, the development of natural fractures is key to the enrichment of shale gas. Thirdly, almost all of the commercial shale gas plays have overpressure. Fourthly, through the migration and transportation of shale gas by relatively short distances, a wide range of migration and accumulation could be achieved. Fifthly, the production patterns based on different perspectives of business returns and resource utilization may impact the production performance of the Fuling shale gas field. Finally, the development of Chinas shale gas needs technology, innovative thinking and longterm perspective, and we must pay attention to the studies of shale gas in the deep marine continental strata and normal pressure strata in the outer of basin. Related Articles | Metrics

Select

Preliminary study of the transitional facies shale gas reservoir characteristics: Taking Permian in Xiangzhong depression as an example. 2016, 23(1): 44-53.  DOI: 10.13745/j.esf.2016.01.004 Abstract ( 3435 )   PDF (2007KB) ( 3811 )   Through observation (Quantang Shaoyang, Beishan Longhui County), measured profile (Jianxincun Lianyuan County and Qixingjie Lianyuan County), sampling and laboratory analysis such as adsorbed gas content, geochemical parameters and reservoir parameters etc. of Longtan & Dalong Formation of Permian in the Xiangzhong depression, we established a composite section of lithologyrock mineralgeochemicalphysical propertiesgasbearing properties of Longtan & Dalong Formation of Permian. The kerogen maceral of the Dalong Formation and Longtan Formation was mainly exinite, vitrinite and inertinite content is less. Samples with total organic carbon greater than 2% accounted for more than 40% of the total longitudinal samples, mainly distributed in the bottom of Dalong Formation and the top of Longtan Formation. The thermal maturity is between 1.10%2.22%, with an average of 1.42% and is at mature to high mature stage. The microreservoir types are mainly mineral micropores and microfracture, followed by organic matter micropore. The mineral micropores mainly include interparticle residual micropores, interparticle dissolution micropores, intraparticle dissolution micropores and intraparticle micropores. Parameters such as thickness of the shale, total organic content, maturity and gas content, oil & gas showing, indicated that the most favorable member for shale gas accumulations is the bottom of the top of Longtan and Dalong Formations with about 80 m thickness which may have good shale gas exploration potential. It is worth noting that shale gas accumulation conditions such as geochemical parameters, mineral composition, reservoir parameters and gas content etc. of the Permian shale in the Sichuan Basin is similar to those in the Xiangzhong depression. They have late peak period of hydrocarbon generation and shallow uplift.The giant Puguang gas field is sourced from the Permian shale. It is needed to pay attention to the transitional facies of shale gas exploration and research of the Permian shale in Sichuan Basin. Related Articles | Metrics

Select

The geological conditions for shale gas accumulation in the LowerMiddle Jurassic, the Frontal Areas of the Altun Mountains. 2016, 23(1): 54-63.  DOI: 10.13745/j.esf.2016.01.005 Abstract ( 3061 )   PDF (1750KB) ( 3651 )   The complex structural evolution of the Frontal Areas of the Altun Mountains involves early faulted depression stage, middle depression stage and late uplift stage, in which continental lacustrine shale developed in the Early Jurassic faulted depression. The whole area is north/westoriented graben or halfgraben defined by syndepositional structure, therefore, laminated lacustrine shale interbeded with siltstone and stone deposite in the Xiaoliangshan sag, Qigequan fault nose zone and Tomorlog bugle. The shale continuously distributes along a northeast band and gradually pinches out from the front zone of mountain to basin. The cumulative thickness of shale is more than 300 m and the effective thickness is between 50 and 70 m, providing a necessary material condition for shale gas reservoir. The study confirmed that average contents of sapropelinite, vitrinite and inertinite are 60.7%, 33.1% and 6.2%, respectively. According to the terminology of Tissot and Welte, the organic matter is dominated by type IIkerogen. Total organic carbon (TOC) ranges from 1% to 4% and the organic matter maturity varies from 0.8% to 2.5% based on the RockEval pyrolytical data of 25 outcrop samples, indicating that the laminated shale has high organic matter abundance and is in oil and gas generation window, reflecting that the source rock quality is good. The average clay mineral contents and siliceous mineral contents are 52.51% and 37.42%, respectively. Compared with marine shale in the North America and Sichuan Basin, the LowerMiddle Jurassic shale contains higher clay mineral contents and lower siliceous mineral contents. The fracture, microcrack, interparticle pore, intraparticle pore and organic matter pore developed in the shale, providing more adsorption sites for methane. The specific surface area of the shale is between 9.13 m2/g and 18.14 m2/g, with an average of 13.43 m2/g; the pore volume varies from 0.0266 cm3/g to 0.0887 cm3/g with a mean of 0.06541 cm3/g; average pore diameter ranges from 25.76 nm to 72.48 nm, averaged at 47.87 nm. The specific surface area decreases with increasing average pore diameter; the pore volume increases with the increase of average pore diameter, the less the pore diameter, the greater the specific surface. The specific surface area increases with TOC and Ro, indicating that organic matter pore from the conversion of kerogen and generation of hydrocarbon contribute more surface area for methane to be adsorbed. The greater the specific surface of the shale, the more the shale gas to be adsorbed in shale. The lime mudstone, limestone and gypsum rocks above the Jurassic shale widely distribute as cap rock, contributing to the protect of shale gas reservoir from destruction. Moreover, the hydrocarbon generation history involving shallow burial in the early stage, deep burial in the middle stage and several stages of hydrocarbon generation, and uplift in the late stage is favorable for the preservation of shale gas reservoir. According to the geological parameters of the formation of shale gas reservoir, there are four favorable areas for shale gas exploration, i.e., Xiaoliangshan area, Qigequan area, Hongshuigou area and Tomorlog area. Related Articles | Metrics

Select

Shale oil accumulation conditions and resource calculation of Western sag shahejie, Liaohe. 2016, 23(1): 64-73.  DOI: 10.13745/j.esf.2016.01.006 Abstract ( 2985 )   PDF (1729KB) ( 3879 )   To identify shale oil exploration potential of Shahejie Formation from Liaohe west sag and the controlling factors of shale oil, focused on Es3 Formation, combined with seismic and logging data, based on an emphasis on organicrich shale hydrocarbon potential, reservoir property and oilbearing assessment by the FIB - SEM, automatic helium porosity determination and BET - BJH tests, the shale oil resource calculation methods of Es3 are analyzed. The results show that, (1) the organic carbon content has a range of 1.0%8.54% with a public value of 2.15%; Ro ranges from 0.32% to 1.57% with a public value of 0.65%, corresponding to the oil window; (2) variety of six micropores such as intergranular pores, grain pore and microfracture with mesopores between 3.9 and 20 nm are rich in shale; (3) Es3 Formation has 1 industrial oil flow, 2 oilenriched layers and 16 oil spots; (4) the shale oil resource calculation methodsunit calculation method were analyzed by probability and statistics, analogy, weight assignment principle and in unit divisionstep calculationcumulative sum manner. It is concluded that Es3 Formation has a good exploration prospect and should be selected as an area with abundant organic matter, moderate thermal evolution, high porositypermeability and oiliness. In contrast, formations with too low thermal evolution or too high content of clay, will be avoided. Related Articles | Metrics

Select

Deposition and distribution of potential shales in China. 2016, 23(1): 74-86.  DOI: 10.13745/j.esf.2016.01.007 Abstract ( 3079 )   PDF (2075KB) ( 3793 )   The tectonic setting that develops shale in China is complex. Located respectively in the northwestern, northern and southern China, Tarim, North China and South China plates are relatively limited while their geological activities are relatively strong. They impact each other and independently controls the tectonic movements and sedimentary environment. Furthermore, the three plates have been influenced greatly by the peripheral plates since Mesozoic. Tectonicsedimentary setting of the plates are very different. For example, South China plate is dominated by marine facies while North China plate is by continental facies. Shales in South China plate developed earlier than that in North China plate. South China plate was principally uplifted to make mountains while North China plate principally subsided to create new basins in Mesozoic and Cenozoic vertically. Also, evolution difference exists latitudinally between Tarim plate and North China plate. The distribution of shales in China is mainly controlled by plate characteristics and the mutual matching between the tectonic and sedimentation since plates and their movements caused migration of subsidence deposition centers in different periods. This kind of migrations have happened for four times respectively in all of the three plates since Paleozoic, i.e., migrating westwards in early Paleozoic in marine settings, migrating away the plate convergence center in Late Paleozoic in transitional environments, migrating eastwards in Mesozoic in continental and transitional settings, and migrating westward in Cenozoic in continental environments. As a result, potential shale and shale gas concentrate in middle China with great alternation of deposition and distinguish migration of distribution. Original geological conditions for shale gas of early Paleozoic in South China are excellent, but gas shales are highly or over matured and strongly reformed. The distribution of favorable areas for potential shales are restricted by tectonic and sedimentary conditions, even the mutual matching of each other. The transition shales are the most potential target, which are always interbedded frequently by sandstones, coal series and limestones with extensive distribution, large total thickness and moderate maturation of organic matter. Continental shales from Mesozoic and Cenozoic in North China plate are controlled by the basin structure, which are the main areas for shale oil exploration. Shale gas exploration and exploitation should be carried out according to their own geological properties and conditions. Related Articles | Metrics

Select

Brittleness evaluation of the Lower Cambrian Niutitang shale in the Upper Yangtze region: A case study in the Cengong block, Guizhou province. 2016, 23(1): 87-95.  DOI: 10.13745/j.esf.2016.01.008 Abstract ( 3063 )   PDF (1526KB) ( 4761 )   The brittleness determines the fracability of shale gas reservoir, which has a significant impact on shale gas exploration and development. Recently, China has achieved a breakthrough of the Lower Silurian Longmaxi shale in the Sichuan Basin and its surrounding areas. Compared with the Longmaxi shale, the Lower Cambrian Niutitang shale has a greater deposition thickness and wider distribution area, which is another significant stratum for Chinas shale gas. In this paper, the brittleness of Niutitang shale was evaluated and analyzed in the study area based on the data of core mechanical test, array sonic logging, mineral composition and fracture parameters. The results show that the relationship between brittleness and brittle mineral content is not a simple positive correlation. The brittleness and fracability of shale are determined by the content of brittle minerals and TOC (total organic carbon), the degrees of thermal evolution (diagenesis stage) and fracture development. Because of the positive correlation between quartz and TOC contents, when the TOC content is less than 6.5%, the increase in the brittleness caused by the increase in the quartz content is greater than the increase in the ductility caused by the increase in the TOC content; when the TOC content is greater than 6.5%, the ductility increases faster than the brittleness, which results in negative correlations of the brittleness with the TOC and quartz contents and low fracture density in the sections with high TOC content. This understanding will guide the exploration and development of shale gas and is very helpful for optimizing drilling and fracture stimulation intervals in southern China. Related Articles | Metrics

Select

Research on the fracture effectiveness of the Lower Cambrian Niutitang shale in southeastern Chongqing and northern Guizhou area. 2016, 23(1): 96-106.  DOI: 10.13745/j.esf.2016.01.009 Abstract ( 3064 )   PDF (2248KB) ( 3663 )   Based on the observation and description of Niutitang shale core fractures in southeast Chongqing and north Guizhou, the effectiveness of fractures was analyzed quantitatively by using logging and regional geological data, meanwhile, the controlling factors of natural fractures effectiveness were researched qualitatively. The relationship between shale gas content and fractures effectiveness was discussed based on the desorption experiments of shale core. The results show that fractures are abundant in Niutitang shale core. The significant difference between deep laterolog resistivity values and shallow laterolog resistivity values revealed the high effectiveness of natural fractures with wild aperture, steep angle and far extending in longitudinal. On the contrary, the low effectiveness of natural fractures due to low angle, narrow aperture, mineral sealing and closely extending in longitudinal, caused the unconspicuous difference between deep laterolog resistivity values and shallow laterolog resistivity values. The effectiveness of fractures is mainly controlled by mineral sealing, denudation, abnormal fluid pressure and tectonic movement. Among them, mineral sealing in fractures caused major damage to the effectiveness, denudation and high abnormal fluid pressure improved the porosity and permeability of shale, thereby improved the effectiveness. The regional tectonic activity produced different effects to the fractures which are in different parts of tectonic position. The effective fractures contributed to the desorption of shale gas, hence the free gas content increased. Moreover, the effective fractures could be the channels for gas migration and exploitation, which improved the permeability of shale reservoir. However, natural fractures with large scale would destroy the sealing property and overpressure of shale reservoir, which will result in the loss of natural gas, therefore, it is not conducive to the preservation of shale gas. Related Articles | Metrics

Select

Fine lithofacies of Chinas marine shale and its logging prediction: A case study of the Lower Silurian Longmaxi marine shale in Weiyuan area, southern Sichuan Basin, China. 2016, 23(1): 107-118.  DOI: 10.13745/j.esf.2016.01.010 Abstract ( 3266 )   PDF (2651KB) ( 4007 )   Fine lithofacies research and prediction of marine shale are of great importance for the successful shale gas exploration. Based on the key parameters of shale and fractures, a lithofacies classification scheme for marine shale is proposed by using TOC content and mineral composition. Combined with the TOC, thin section, Xray diffraction and other core testing data, differences of lithofacies for Longmaxi Formation in the Weiyuan area have been analyzed. Furthermore, based on probabilistic neural network (PNN), shale lithofacies of Longmaxi Formation in the Weiyuan area have been predicted by using well log, and the lithofacies associations have been characterized in detail: ① There are 11 lithofacies for Longmaxi Formation in the Weiyuan area, 5 kinds of organic rich shale facies, 6 kinds of organic lean facies. ②Among these 11 lithofacies, the organic rich siliceous shale, organic rich carbonatesiliceous shale and organic rich siliceouscarbonate shale, which contain high TOC content and high brittleness, are favorable lithofacies for shale gas exploration. ③The favorable lithofacies are mainly concentrated on the lowermost part of the Longmaxi Formation, in which thickness increased from northwest to southeast with different favorable lithofacies associations in different part. In the northwest, W1 well has thinner favorable lithofacies associations with thickness of 20 m, mainly composed of organic rich siliceous shale and organic rich carbonatesiliceous shale. W2 well, located in the central part, has different favorable lithofacies associations with thickness of 30 m, mainly consisting of organic rich siliceous shale, organic rich carbonatesiliceous shale, organic rich siliceouscarbonate shale and thin organic rich clay shale. In the southeast, the favorable lithofacies associations of W4 well are mainly composed of organic rich siliceous shale, organic rich carbonatesiliceous shale, organic rich siliceouscarbonate shale and thick organic rich clay shale, which has thickness of 35 m. Related Articles | Metrics

Select

Lithofacies characterization of Longmaxi Formation of the Lower Silurian, southern Sichuan. 2016, 23(1): 119-133.  DOI: 10.13745/j.esf.2016.01.011 Abstract ( 3302 )   PDF (2930KB) ( 4238 )   Lithofacies characterization is fundamental to the geologic evaluation and favorable layers and plays selection in shale gas exploration. Based on the outcrops and drilling data, a lithofacies classification method for marine shale was developed to finely characterize the lithofacies of the Upper Ordovician WufengLower Silurian Longmaxi shale through analysis of mineral composition, thin section, geochemical and logging data. Four preliminary conclusions were obtained: (1) Ternary diagram combined with sedimentary microfacies is an effective method in the classification of lithofacies types and their association for marine shale. (2) Six types of lithofacies were developed in the WufengLongmaxi shale in the Southern Sichuan Basin and they can be further classified into three types of lithofacies association, among which siliceous and calcareoussiliceous mixed shales are typical in (semi)deep water environment, argillaceous and argillaceouscalcareous mixed shales are dominant in semideep to shallow water environment, and argillaceoussiliceous mixed shale is developed in both shallow and deep water environment. (3) The basic features of each lithofacies association with different genesis, including mineral composition, matrix fabric, palaeontology, organic matter richness and log response, vary greatly with the decrease of water depth, stronger hydrodynamic force, and the increase of terrestrial input. (4) With the control of sea level change, the lithofacies associations deposited in deep water shelf, including siliceous, calcareoussiliceous shale and argillaceoussiliceous mixed shale are principal producing pay, while the lithofacies associations deposited in semideep to shallow water shelf, including argillaceous, argillaceoussiliceous shale and argillaceouscalcareous mixed shale, are the caprock of the producing pay. They form a selfsealed and selfstored reservoircap association vertically, and the former, which is rich in siliceous and organic matter, is favorable lithofacies to serve as producing pay, and the latter, which is rich in clay and deficient in organic matter, is favorable lithofacies to serve as capping bed. Related Articles | Metrics

Select

The heterogeneity of shale gas reservoir in the Yanchang Formation, Xiasiwan area, Ordos Basin. 2016, 23(1): 134-145.  DOI: 10.13745/j.esf.2016.01.012 Abstract ( 3070 )   PDF (3019KB) ( 3650 )   Chang 7 and Chang 9 shales are the main reservoir for shale gas enrichment in the Yanchang Formation of Ordos Basin. The heterogeneity of the macro framework, geochemical parameters, microscopic pore structure and mechanical parameters was analyzed on the basis of the core analytical data and logging interpretation results of lacustrine shale. The results show that the density and frequency of siliceous lamina are high and the heterogeneity is strong. The siliceous lamina can effectively improve the property of shale, and provide favorable space for free gas enrichment and migration. Shale section with stronger heterogeneity has better physical properties for the free gas seepage and enrichment. There are more siliceous lamina developed in the shale section with weak heterogeneity where the physical properties are poor. The stranded hydrocarbon content is high. There is no hydrocarbon migration and hydrocarbon expulsion is difficult, so adsorbed gas gets more and more, and it is easy to be enriched. Therefore, the lacustrine shale gas enrichment mechanism is controlled by its heterogeneity. Strong heterogeneity shows high content of brittleness mineral, which is advantageous to the shale reservoir fracturing. Related Articles | Metrics

Select

Adsorption characteristics of Chang 7 shales from Triassic Yanchang Formation and the controlling factors, the Ordos Basin. 2016, 23(1): 146-153.  DOI: 10.13745/j.esf.2016.01.013 Abstract ( 3029 )   PDF (1235KB) ( 3718 )   The Chang 7 Member in the ZhidanGanquan region of the Ordos Basin is a set of dark mudstones and shales deposited in a deep lacustrine setting. With high TOC, type Ⅱ1 organic matter and Ro mostly of 0.6%1.2%, the Chang 7 mudstones and shales are confirmed to be the principal source of the widely distributed oils in the Ordos Basin. In order to discuss the adsorption characteristics of Chang 7 organicrich shales, we analyzed the test results of isothermal adsorption, the content of organic carbon, XRD, thermal maturity and liquid nitrogen adsorption of 16 shale samples chosen from the study area. It turns out that the Langmuir volume of the Chang 7 shales varies between 0.56 m3/t and 4.43 m3/t. With the increase of pressure, the Langmuir volume rises correspondingly until the pressure reaches a certain level. The Langmuir volume has a positive correlation with the organic carbon content, clay mineral content, specific surface area and pore volume. In contrast to many marine shales, the Langmuir volume of the Chang 7 lacustrine shale has a negative correlation with quartz content, which is probably due to the fact that the source of the lakedeposited quartz is of terrestrial detrital origin. The relation of the Langmuir volume and thermal maturity (Ro) of the studied shales is negative when the Ro is less than 0.9% or so but becomes positive as the Ro is more than 0.9%. Based on the comprehensive evaluation, it is found that the TOC content and clay mineral content have the most significant effect on adsorption characteristics, while the specific surface area is a more direct factor. Related Articles | Metrics

Select

Qualitativequantitative multiscale characterization of pore structures in shale reservoirs: A case study of Longmaxi Formation in the upper Yangtze area. 2016, 23(1): 154-163.  DOI: 10.13745/j.esf.2016.01.014 Abstract ( 3086 )   PDF (1924KB) ( 3733 )   Microscopic pore structures and their primary controlling factors on the Lower Paleozoic Longmaxi Shale in the upper Yangtze area were investigated using a fieldemission scanning electron microscope, highpressure mercury intrusion, lowtemperature nitrogen adsorption and carbon dioxide adsorption. Pore morphology and pore size distributions from macropores to micropores were successfully characterized. Combined with the geochemical parameters and mineral composition, the factors influencing the nanoscale pore structure were analyzed. The results indicate that the pores in the shale reservoirs are generally nanoscopic and can be classified into four types: organic pores, intraparticle pores, interparticle pores and microfractures, of which the most common are organic nanopores and interparticle pores between clay particles. The combination of the highpressure mercury intrusion, lowtemperature nitrogen adsorption and carbon dioxide adsorption curves enabled the description of the pore size distributions for micro, meso, and macroporosity. The pore size distributions are multimodal including not only predominant mesopores (250 nm) but also a certain amount of micropores (<2 nm). The nanoscale pores primarily consist of slitshaped pores with parallel plates and inkbottle type pores. Micropores and macropores account for most of the pore volume, whereas those with a diameter less than 5 nm account for most of the specific surface area. The TOC and clay mineral contents are the primary factors controlling the nanoscale pore structure characteristics, whereas micropores and macropores are mainly controlled by the TOC content. Mesopores and macropores are primarily determined by the content of clay minerals and brittle minerals, respectively. Related Articles | Metrics

Select

Characteristics and influencing factors of nanopores in the Middle Jurassic Shimengou Shale in Well YQ - 1 of the Northern Qaidam Basin. 2016, 23(1): 164-173.  DOI: 10.13745/j.esf.2016.01.015 Abstract ( 1506 )   PDF (1757KB) ( 1277 )   The Northern Qaidam Basin (NQB) is a typical continental limnic basin and is also one of the basins with shale gas potential. In this paper, the characteristics and influencing factors of nanopores of the shales in the Middle Jurassic Shimengou Formation of Well YQ - 1 in the Yuqia area of NQB were studied by using nitrogen gas adsorption, total organic carbon content, organic matter maturity, and Xray diffraction analyses. The results showed that the nanopore structures in the Shimengou shale are complex, and these nanopores can be subdivided into two types based on the nitrogen adsorptiondesorption curves and pore diameter distribution. The first type mainly consists of the airtight pores with one end closed and the open parallel plateslit pores, and the pore diameters are in a range of 35 nm. The second type mainly consists of the airtight pores with one end closed and the open inclined slit pores, and the pore diameters are characterized by a bimodal distribution, peaking in a range of 35 nm and 814 nm. The micropore and mesopore with an aperture smaller than 50 nm provided the dominating specific surface area and pore volume. The volume of micropores, mesopores and total pores showed a positive correlation with the clay contents. The pores of organic matter were less developed at a low maturity. The H9 shale, characterized by a high TOC content, shows a negative correlation between the TOC content and the volume of micopores, mesopores and total pores, while the H8 shale, characterized by a low TOC content, shows no correlation. Pore structures and diameter distributions are related to the hydrodynamic conditions of depositional environment. The clay content is a key factor controlling the nanopore development in shale, and the TOC content and depositional environment also have a certain influence. Related Articles | Metrics

Select

Reservoir characteristics and its control on gasbearing properties of the 5th Member of the Triassic Xujiahe Formation continental shale in the Sichuan Basin of China. 2016, 23(1): 174-184.  DOI: 10.13745/j.esf.2016.01.016 Abstract ( 3016 )   PDF (2113KB) ( 3628 )   Continental shale sequences are well developed in the Sichuan Basin, but the characteristic of complex petrology and lithology combination, strong heterogeneity and unclear reservoir property restricted the gas exploration and development process. Using experimental methods such as whole rock Xray diffraction, FESEM, high pressure mercury injection, isothermal adsorption, this study investigated the reservoir geological characteristics of the 5th Member of the Triassic Xujiahe Formation continental shale according to the petrologic features, micropore structure and physical property, and the major geological factors influencing reservoir development. On this basis, this study also clarified the controlling effects of reservoir on the natural gas content and occurrence state. The research shows that there are three kinds of superpositiontype reservoir structure in the 5th Member of the Xujiahe Formation (T3x5) in vertical, which are sandrich type, interbeded type and mudrich type. The densification of the reservoir is very serious, but the reservoir physical property of mudstone is better than that of siltstone and fine sandstone. The reservoirs in T3x5 have a small amount of primary and intergranular dissolution pore, which was caused by strong diagenesis and the sedimentary environment from distant part of the delta to shore shallow lake with low hydrodynamic energy. The large quantitative of flake intergranular pores, organic pore, and microfractures in shale make it being main contribution to the reservoir property. Besides, the continental shale gas also has mixing features of two kinds of gases, i.e., adsorption gas and free gas. However, adsorption gas is dominant, accounting for 84.9% of the total gas content. Gas occurrence state and gas content are controlled by the reservoir lithology, microscopic pore structure and reservoir physical property. Related Articles | Metrics

Select

Petrology Types and Organic Geochemical Characteristic of Shale in the Western Depression, Liaohe. 2016, 23(1): 185-194.  DOI: 10.13745/j.esf.2016.01.017 Abstract ( 3136 )   PDF (1837KB) ( 3678 )   Based on the core observation of the Western Sag of Liaohe, combined with rock slice and Xdiffraction quantitative analysis of whole rock, this study improves the lacustrine mudstone lithology classification method. According to the new classification scheme, shale can be divided into three types: clay shale, felsic shale and mixed shale. Clay shale is characterized by dense layer structure and organic layered enrichment. It is dominated by clay minerals and developed in the environment with relatively weak. Terrestrial input. The felsic shale mainly consists of mudscale quartz feldspar with unclear layered structure under microscope. It is developed in the freshwater sedimentary environment with strong terrigenous input. Mixed shale consists of clay minerals, carbonate and felsic minerals, no main composition. Organic matter is dominated by lucstrine alage. Organic laminae is interbedded with clay or carbonate laminae. It is developed in occlusion lacustrine environment with brackish water to salt water.Organic geochemical analysis and hydrocarbon generation kinetic experiments show that the organic matter of the clay shale and mixed shale (including carbonate type) developed in the semideep to deep lake with laminated structure is dominated by type ⅠⅡ1 It has strong hydrocarbon generation potential, and is followed by felsic shale and massy mudstones. Mixed shale are mainly distributed in the Du2 and Gaosheng sections of the upper 4th Member of Shahejie Fm of Pansan subsag. Clay shale are mainly distributed in the Du1 section of the upper 4th member of Shahejie Fm in the Dujiatai and Shuguang slope areas. Mixed shale area is the main direction of unconventional oil and gas exploration of the oil field. Related Articles | Metrics

Select

Study on reservoir space and evolution process of Longmaxi shale in Fenggang area of northern Guizhou. 2016, 23(1): 195-205.  DOI: 10.13745/j.esf.2016.01.018 Abstract ( 3042 )   PDF (1704KB) ( 4183 )   The study of shale reservoir space is one of the core contents of the shale oil and gas, and the shale pores have a great influence on the reservoir capacity and the percolation feature of the reservoir. Microscopic analyses of thin sections, scanning electron microscopy, focused ion beam milling(FIB), field emission SEM (FE - SEM) and Energy Dispersive Spectrometer (EDS) were used to determine the genesis, size, morphology, distribution, connectivity of the Longmaxi shale reservoir in the study area. Based on the genesis of reservoir space and the developing positions of the pores, the classification for the reservoir space was analyzed. The reservoir spaces of Longmaxi shale in the study area are divided into inorganic pores, organic pores and fractures. According to the diagenesis process of the shale, mechanical compaction, thermal evolution mechanism, clay mineral transformation, dissolution were considered to qualitatively discuss the formation and evolution process of the reservoir spaces. The reservoir spaces of the Longmaxi shale in the study area mainly include pores between clay mineral platelets, clay floc pores, pores within organic matter and fractures. Organic matter pores are the products of shale evolution to a certain stage, and not all the shale reservoir develop organic matter nanometer pores. The formation and preservation of organic matter nanometer pores are influenced by various factors. Related Articles | Metrics

Select

Pore characteristics and significance of the Longmaxi Formation gas shale reservoirs in northwestern Guizhou, China. 2016, 23(1): 206-217.  DOI: 10.13745/j.esf.2016.01.019 Abstract ( 3179 )   PDF (1754KB) ( 4204 )   The Lower Silurian Longmaxi Formation marine shales, with high organic matter abundance and high thermal maturity, have been known as the main shale gas reservoirs in southern China. Pore characteristics and the influencing factors for pore development were investigated by samples collected from the Well Xiye1 and Well Tongye1 in northwestern Guizhou, China. FESEM implied that nearly all pores are nanometerscaled. Pores could be divided into mineral matrix pores (including interparticle pores and intraparticle pores), organic matter (OM) pores and microfracture pores. OM pores are the most prevalent ones within these shale samples. Results of other experiments show that the TOC content averages 3.80%; the Ro value averages 2.73%; and the total porosity averages 1.56%. The shales are rich in clay and detrital minerals (quartz and feldspar), with average contents of 32.42% and 43.97%, respectively. The average BET specific surface area is 16.98 m2/g; the BJH total pore volume is 0.0137 mL/g; and the pore diameter is 33.75 nm. Regression analyses suggest that the TOC content is the key influencing factor for pores development. The total porosity is positively correlated with TOC and detrital mineral content, but is negatively correlated with clay mineral content. Besides, saturated adsorption amount averages 2.42 m3/t and there is a strong positive linear correlation between saturated adsorption amount and the TOC content, which infers that OM pores may provide a main space for gas storage. Saturated adsorption amount also shows strong positive linear correlation to total porosity, detrital minerals content, the BET surface area, and the BJH total pore volume. Related Articles | Metrics

Select

The controlling effect of contemporaneous reverse faults on alluvial fan depositional architecture: A case study of Triassic Lower Karamay Formation at the northwestern margin of the Junggar Basin. 2016, 23(1): 218-228.  DOI: 10.13745/j.esf.2016.01.020 Abstract ( 2914 )   PDF (2174KB) ( 5788 )   This paper explores the depositional architectural characteristics of alluvial fan associated with contemporaneous reverse faults at compressional basin margin, for example of Triassic Karamay Formation at the northwestern margin of the Junggar Basin. Based on lithofacies study, hierarchical bounding surface analysis, outcrops and subsurface analogues as well as welltoseismic integration, the combination types of contemporaneous reverse faults at compressional basin margin are summarized. According to this study, the distribution of alluvial fan bodies at compressional basin margin was mainly controlled by the combination of contemporaneous reverse faults. Different combinations of contemporaneous reverse faults resulted in the scale and morphology variation between different fans. In the combination of multiple parallel faults and strikeslip faults, the movement of dextral strikeslip fault resulted in continuous erosion of the source provenance which eventually evolved into an accommodation area; under this condition the fan bodies presented a rapid retrograding thinbed overlying pattern of banding shape updipping towards the provenance. Meanwhile, the translation of strikeslip fault had an impact over the sediment transportation from provenance; thus the fan bodies could also display a lateral migration overlaying pattern. Where crossshaped contemporaneous reverse faults act strongly, a multiperiod thick vertical superimposed fan combination is formed. Related Articles | Metrics

Select

Geological characteristics and deep water hydrocarbon accumulation patterns of transformed passive continental marginal basins: A case from basins of West Africa margin in Equatorial Atlantic. 2016, 23(1): 229-239.  DOI: 10.13745/j.esf.2016.01.021 Abstract ( 3052 )   PDF (1851KB) ( 3639 )   Based on predecessors achievements and petroleum exploration data from new findings, this paper analyzes the geological characteristics and deepwater hydrocarbon accumulation patterns of the transformed passive continental margin basins in the Equatorial West Africa, which are controlled intensely by transform fault. According to the structural interpretation and stratigraphic analysis, it can be seen that the basin shape, basement faults, deformation sequence and regional stress are all controlled by this transform fault. These basins have undergone four phases of evolution: the intracontinental sedimentary phase during pretransforming, the intracontinental sheared phase during rifting, the continentocean transform phase during transpression and the passive marginal phase during thermal subsidence. Four regional unconformity faces that migrated from east to west were formed. Three different sedimentary sequences were filled, including lacustrine clastic rocks in the intracontinental sheared stage, mainly clastic rocks of continental and littoralneritic facies in the continentocean transform stage, and mainly clastic rocks of marine facies in passive marginal stage. Some geological structural characteristics, such as narrow continental shelf, steep continental slope and high angle transtensional fractures, revealed that the transformedridge or platform could be easily developed. Generally, small sources migrated short distances and accumulated quickly near coasts in deepwater areas, forming sandrich small fans or fan complexes which were superposed vertically and showed apronstyle in lateral. Deepwater petroleum exploration should focus on stratalithological and anticlinal structural traps in continentocean transform stage and early passive marginal stage. Related Articles | Metrics

Select

Quantitative prediction of tectonic fractures of Lower Jurassic Ahe Formation sandstones in Dibei gasfield. 2016, 23(1): 240-252.  DOI: 10.13745/j.esf.2016.01.022 Abstract ( 3046 )   PDF (2492KB) ( 3577 )   The lower Jurassic lowporosity and lowpermeability tight sandstone is a major reservoir of Dibei gas field in the Kuqa depression, Tarim Basin. As a migration channel and reservoir space, the development features and distribution of tectonic fractures is the key to oil and gas exploration and development. This study adopts the latest 3D structural map of the Dibei area, taking geological setting, geometry of strata, and faults into consideration, and divides the Ahe Formation into three sections. Based on the measured rock mechanics parameters, a three dimensional elastic finite element numerical simulation method is used to calculate the maximum principal stress of Pliocene structural stress field in the Kuqa depression. The calculated results matched the observed results. Under the restraints of 11 wells, the two factor method is proposed to simulate the development of tectonic fractures by means of rock failure value and strain energy density together to predict tectonic fracture density of the three sections of the Ahe Formation. The results show that the Yinan2Dixi1Dibei104 area and the area to the south of Dibei101Yinan5 as well as the area to the west of Tuzi1 and to the north of Tuzi3 have the highest density of fractures; in addition，the J1a23 formation is easier to be cracked than the J1a1 formation. The prediction results of tectonic fractures in the Ahe Formation provide a new geological reference for the exploration and development of Dibei gasfield. Related Articles | Metrics

Select

Application of fluid inclusion in evaluating holes filling strength of carbonate reservoir in strata environment：A case study from Tarim Basin. 2016, 23(1): 253-263.  DOI: 10.13745/j.esf.2016.01.023 Abstract ( 3117 )   PDF (1837KB) ( 3814 )   Marine carbonate has been an important hydrocarbon prospecting domain of our country, in which the secondary space, such as karst cavity, is an important reservoir. However, the unpredictable of the buried karst reservoir is a challenge for carbonate hydrocarbon prospecting. Dissolutiondeposition equilibrium theory used in carbonate indicates that there was little fluid inclusion in dissolution zone or dissolutiondeposition equilibrium zone and many fluid inclusions were generated in deposition zone accompanying new mineral generation. The developmental phases of fluid inclusions suggested the fluid active phases during the geological history. Based on this, the following idea was deduced: the packing action is more obvious where there are more developmental phases of fluid inclusion, and thus the reservoir is relatively worse, and vice versa. In this paper, based on dissolutiondeposition equilibrium theory, using fluid inclusion data of Ordovician holes filling in Tarim Basin, combined with geology of buried history, the buried karst reservoirs packing timespace history of the research area was restored, and the karst reservoir zones of varying degrees of packing were fixed, and the beneficial reservoir area can be located under reverse thinking. The application of this method to the Ordovician carbonate formation of Tarim Basin area proved its feasibility; the result shows that the prediction of the fluid inclusion method is almost identical with the core observation and drilling or logging results. By this approach, we can predict the better reservoir correctly. On the whole, the fluid inclusion approach provides a feasible method in evaluating holes filling strength in strata environment. This is significant in theory and practice for the buried karst reservoir evaluation. Related Articles | Metrics

Select

Geochemical characteristics of the Chongba leucogranites, southern Tibet: Formation mechanism and tectonic implications. 2016, 23(1): 264-276.  DOI: 10.13745/j.esf.2016.01.024 Abstract ( 3312 )   PDF (1564KB) ( 4005 )   The Chongba leucogranite pluton is situated in the eastern part of the Greater Himalayan leucogranite belt. Geochemical data show that these rocks are characterized by high SiO2(73.87%74.95%), Al2O3(14.20%14.74%), K2O(4.44%4.89%), K2O/Na2O(1.191.42), A/CNK values (1.181.22), and enrichment in Rb, Th, U, depletion in Ba, Nb, Sr, Zr, and strong negative Eu anomalies (δEu=0.270.37). These features suggest that they are high potassium calcalkaline and peraluminous Stype granites. The high Rb/Sr (2.68.6) and low CaO/Na2O (0.180.20) ratios imply that the source rocks were probably pelites. The relatively high (87Sr/86Sr)i(0.7631990.778799) and low εNd(t) (-16.7-16.3) compared with those of the metasedimentary rocks in the Greater Himalaya crystalline complex (GHC), indicating that the leucogranites were generated from partial melting of the GHC metasedimentary rocks. The features of high (87Sr/86Sr)i and low Sr content, and the Rb/Sr values decreasing with increased Ba content indicate that the Chongba leucogranites were derived from muscovite dehydration melting of the GHC metapelite under waterabsent condition, which is probably closely associated with the structural decompression caused by the extensional decollement of the south Tibet detachment system (STDS). Related Articles | Metrics

Select

Timefrequency analysis of the Earths natural pulse electromagnetic field signal before and after the Lushan MS 7.0 earthquake based on NSTFTWVD transform. 2016, 23(1): 275-286.  DOI: 10.13745/j.esf.2016.01.025 Abstract ( 2976 )   PDF (1782KB) ( 3553 )   The present paper aims at the nonstationary characteristics of Earths natural pulse electromagnetic field (ENPEMF) signals by using the normalized STFT - WVD(NSTFT - WVD) transformation, and the main analysis focuses on timefrequency characteristics of the ENPEMF signal before Lushan MS 7.0 earthquake. By comparing shorttime Fourier transform(STFT)and WignerVille distribution(WVD)transformation with the linear frequency modulation signal, this paper analyzes their advantages and disadvantages of both time and frequency focusing performance. NSTFT - WVD transform method can give us the better timefrequency aggregation and inhibits the cross terms. The results show that NSTFT - WVD transform can reflect the real ENPEMF signal timefrequencyenergy spectrum distribution before and after the earthquake, which could render more obvious silent state in entire frequency and sustained 12 days before the earthquake. The timefrequency representation of data channels 2 and 3 are basically consistent with this characteristic, which well represents the feature of impending earthquake precursors. Related Articles | Metrics