10 January 2019, Volume 30 Issue 1
    

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  • Controlling factors on shale gas accumulations of Wufeng-Longmaxi Formations in Pingqiao shale gas field in Fuling area，Sichuan Basin
    Guo Xu-sheng
    Natural Gas Geoscience. 2019, 30(1): 1-10. https://doi.org/10.11764/j.issn.1672-1926.2018.12.007
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    Pingqiao shale gas field in Fuling area，located in the fault anticline of Fenglai Syncline，has a narrow-abrupt slope belt.The proved geological reserves are 1 389.17×108m3  in the Wufeng-Longmaxi Formations，suggesting Pingqiao shale gas field possesses good potential for shale gas exploration.In order to study the features，major factors controlling the accumulation and high productivity and the reasons for production variance from different wells in Pingqiao shale gas field，the article makes a detail analyses of Pingqiao shale gas field based on drilling，logging，seismic and experimental data.The results show that:(1)The  thickness of Pingqiao shale gas layer（TOC≥1%） is 115-155m；the thickness of quality layer（TOC≥3%）at the bottom is 36-40m，the shale gas is featured by high reserves（reserve abundance 12.68×108m3/km2），high pressure of shale gas accumulation（pressure ratio 1.56），high production of wells（average testing production 21.99×104m3/d）.(2)Deep shelf quality shales and the faults showing weak slipping，good sealing and no pressure-leaking area are found in surrounding area，being the main controlling factor to shale gas accumulating and high production in Pingqiao shale gas field.(3)Micro-fractures，structural location and depth are also key factors for various productions of wells in Pingqiao shale gas field under the similar accumulating circumstances.


  • Reservoir characteristics of Longtan Formation shale gas in Huayingshan area，eastern Sichuan Basin
    Liu Hu, Cao Tao-tao, Qi Ming-hui, Wang Dong-qiang, Deng Mo, Cao Qing-gu, Cheng Bin, Liao Ze-wen
    Natural Gas Geoscience. 2019, 30(1): 11-26. https://doi.org/10.11764/j.issn.1672-1926.2018.10.011
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    In order to reveal shale gas reservoir characteristics and controlling factors of the Longtan Formation transitional organic-rich shales in Huayingshan area，eastern Sichuan Basin，organic geochemistry，mineral composition，and pore structure parameters were analyzed.The results show that the Longtan Formation shales are characterized by high TOC contents averaged at 3.16%.The kerogen type was mainly type Ⅲ，and the average vitrinite reflectance value is 1.2%，reaching moderate to high maturity stage.The clay mineral is concentrated in the Longtan Formation shale，with an average content of 66.24%，which is mainly composed of I/S mixed layer and illite.The main pore space is composed mainly of interbedded pores related to clay minerals and microcracks，and the organic matter pores are not developed.These shales usually have a high specific surface area and pore volume，with mean values of 27.47m2/g and 0.042cm3/g，respectively，which is approximate to the marine Longmaxi Formation shales in southern China.The specific surface area and pore volume have a negative relationship with TOC content，but have a significant positive relationship with clay mineral content，illustrating inorganic matter pores are the main contributor to shale pore space other than organic matter pores.The micro- to mesopores presenting in I/S mixed layer and meso- to macropores in illite are the main components to construct pore system of shales.
  • The coupling relationship between material composition and pore microstructure of southern China marine shale
    Li Wen-biao, Lu Shuang-fang, Li Jun-qian, Zhang Peng-fei, Chen Chen, Wang Si-yuan
    Natural Gas Geoscience. 2019, 30(1): 27-38. https://doi.org/10.11764/j.issn.1672-1926.2018.10.001
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    To explore the coupling relationship between material composition and pore microstructure，30 marine shale samples with high-over maturity from the Wufeng and Longmaxi Formations，Southern China were analyzed by using nitrogen adsorption method.According to the shape of hysteresis，3 types of shales are identified.The results show that clay mineral mainly develops slit pores ranging from micropore (<2nm) to macropore (>50nm)，while organic matter mainly develops inkbottle pores with the size of mesopore (2-50nm).Whether in BET specific surface area (SSA) or total pore volume (PV)，mesopores always makes the largest contribution.Micropores make the second largest contribution to the SSA，while macropores offer moderate PV.The SSA of microporeis mainly provided by organic matter，and clay minerals mainly contribute to the SSA of mesopores and macropores.Clay minerals mainly provide macropore volume，while organic matter mainly contributes to micropore and mesopore volume.The shale samples generally show three stages of fractal characteristics，and in the range of different pore size，the inkbottle pores are more complex than slit pores.The results are helpful to understand the law of gas accumulation and migration.

     
  • Structural and sedimentary basin transformation at the Cambrian/Neoproterozoic interval in Tarim Basin:Implication to subsalt dolostone exploration
    Chen Yong-quan, Yan Wei, Han Chang-wei, Yan Lei, Ran Qi-gui, Kang Qian, He Hao, Ma Yuan
    Natural Gas Geoscience. 2019, 30(1): 39-50. https://doi.org/10.11764/j.issn.1672-1926.2018.10.016
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    As one of the important fields of oil and gas exploration in Tarim Basin，sub-salt dolomite in Cambrian has been restricted by the poor acknowledge of source rocks and reservoirs distribution.Based on the study of the unconformity characteristics of the Cambrian/Neoproterozoic，the seismic interpretation and mapping of the Cryogenian-Sinian and Middle-Lower Cambrian，this paper discussed the sedimentary basin transformation before and after Kalpin movement at the Cambrian/Neoproterozoic interval，in order to solve the problem of hydrocarbon-bearing depression and the dolomite reservoir distribution of the Xiaoerbulake Formation，guiding the optimal exploration zone.Results show that the Kalpin movement has more influence on the southern part of Tarim Basin than the northern part.In the southern part of the western platform，the Lower Cambrian onlaps towards southern paleo-continent.In the northern part of the basin，there is mainly parallel unconformity contact，and the stratigraphic sequence of the Lower-Middle Cambrian is complete.Kalpin movement caused a major paleo-structure transformation from the North-East in Neoproterozoic to the east-west and north/south in Cambrian，and sedimentary transformation from rifted-sedimentary to platform-basin sedimentary.According to the palaeogeography of the Cryogenian-Sinian and Early-Middle Cambrian，the most abundant Neoproterozoic-Cambrian source rocks in the Tarim Basin distribute in the Manxi Depression.The dolomite reservoirs of Xiaoerbulake Formation mainly distributes around the Manxi Depression.It is suggested at last that Central Tarim Uplift，Gucheng area and Lunnan areas should be preferentially prospected.
  • Diagenesis and its effect on pore and permeability of Donghe sandstone in Hanilcatam area，Tarim Basin
    Chen Xiu-yan, Jia Jin-hua, Cui Wen-juan, Zhang Li-ping, Zhou Bo, Shen Yin-min, Chen Yan-gui
    Natural Gas Geoscience. 2019, 30(1): 51-61. https://doi.org/10.11764/j.issn.1672-1926.2018.10.022
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    Based on the analyses of core observation，thin slice identification，scanning electron microscope，cast thin slice，cathodoluminescence and physical property data，the diagenesis，pore formation and its effect on pore and permeability of Donghe sandstone，deep buried high quality reservoir in Hanilcatam area of Tarim Basin are studied.Donghe sandstone is in the stage of the middle diagenesis A2-B.The cementation and dissolution of carbonate cements are important diagenetic events.Carbonate cementation of early diagenesis，low geothermal gradient and short term deep burial can enhance the anti-compacting capacity of the reservoir，which is good for keeping more primary pores.The carbonate cementation of later diagenesis can fill in intergranular pores and intragranular pores produced by organic acid dissolving particles，and the later dissolution of carbonate cements can also form secondary pores.The content of carbonate cement is negatively correlated with the porosity and permeability of the reservoir vertically and in the plane，so using the content of carbonate cement can predict and evaluate the physical property of the reservoir.
  • Sequence stratigraphy and depositional evolution of the Bashijiqike Formation  in the western Tabei Uplift，Tarim Basin
    Liu Yong-fu, Xia Hui, Sun Qi, Lin Chang-song, Zhao Hai-tao, Li Hao, Huang La-mei, Zhang Zhi-yuan
    Natural Gas Geoscience. 2019, 30(1): 62-73. https://doi.org/10.11764/j.issn.1672-1926.2018.10.003
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    Based on comprehensive drilling，logging and seismic data，with application of classic sequence stratigraphy theory，the sequence stratigraphic framework of Early Cretaceous Bashijiqike Formation in the western Tabei Uplift of Tarim Basin was established.According to the regional unconformities，abrupt interface of sedimentary facies and the change of transforming surface of stratigraphic accumulation type，4 sequence boundaries were identified in the study area.One second-order sequences of Bashijiqike Formation in the study area were recognized，which can consist of a complete regional lake-level rise and fall cycles.The second-order sequences can be further divided into 3 third-order sequences.Each sequence was further divided into low stand system tracts，transgressive and high stand system tracts.Fan delta and braided river delta sedimentary systems are identified，based on the analysis of core observation，well logs and seismic data within sequences in the study area.The fan deltas of Bashijiqike Formation developed in the study area are mainly regressive type and the braided river deltas are progressive type and degenerate type.The distribution and evolution of depositional systems and their controlling factors in the study area are analyzed.Then，the depositional evolvement model of Bashijiqike Formation was established.
  • Formation mechanism and distribution regularity of Ordovician Ma55 dolomite reservoir in Ordos Basin
    Zhang Dao-feng, Yao Jing-li, Gao Xing, Xi Ming-li, Zhao Hui-tao, Yan Xiao-xiong, Fu Xun-xun
    Natural Gas Geoscience. 2019, 30(1): 74-82. https://doi.org/10.11764/j.issn.1672-1926.2018.11.007
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    Based on dolomite structure analysis，the formation mechanism of Ordovician Ma55 dolomite was discussed with geochemistry test data of carbon isotopes，oxygen isotopes，strontium isotopes，and order degree.The study showed that reservoir-effective lithology is mud-powder crystal dolomite and powder crystal dolomite.The mud-powder crystal dolomite is non-cathode luminescence with 0.71 order degree，0.1‰ , δ13C，and -6.3‰ δ18O，while the powder crystal dolomite is mainly dark-red cathode luminescence with 0.85 order degree，-0.68‰ δ13C，-6.58‰ δ18O.The carbon and oxygen isotopes of mud-powder crystal dolomite and powder crystal dolomite are roughly equivalent to the value of seawater in the Middle Ordovician.It reflected that dolomitization fluid is related to the same period seawater，with characteristics of reflux-seepage dolomitization.Combined with palaeogeographic background，the reflux-seepage dolomitization model was established.The dry and hot paleoclimate，which had the ability to form Mg-rich brine in Ma55 deposition period，is the key to form Ma55 dolomite.Syngenetic dolomitization prepared the ground for the spread of dolomite，provided effective seepage channel for supergene dolomitization，and was conducive to the preservation of pores in burial period.Near the paleouplift area，the whole segment is dominanated by dolomite.Influenced by southern slope of the Yimeng paleocontinent，the middle and upper segment is dominanated by dolomite in Yulin-Shenmu area，and the middle segment is dominated by dolomite in Jingbian-Ansai area.The whole dolomite segment and the middle dolomite segment are favorable exploration targets.

  • Pore evolution and its quantitative model of low porosity and low permeability reservoir of Chang 101 in Shanbei area，Ordos Basin
    Chen Jun-fei, Li Qi, Zhu Ru-kai, Mao Zhi-guo
    Natural Gas Geoscience. 2019, 30(1): 83-94. https://doi.org/10.11764/j.issn.1672-1926.2018.11.004
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    Porosity evolution of reservoir is a key and difficult point of the study on hydrocarbon accumulation and regional reservoir evaluation.Diagenesis of low permeability reservoir dominates pore evolution.Through cores，thin sections，SEM and other methods，reservoir characteristics，diagenesis and relationship with physical property of Chang 101 reservoir in the Shanbei area of Ordos Basin were systematically studied，and the diagenetic evolution sequence was established.Combined with burial history，geothermal history and hydrocarbon filling history，pore evolution model were qualitatively and quantitatively studied and porosity of the critical period of hydrocarbon accumulation were restored.The results show that types of reservoir sandstone are arkose and lithic arkose.It is a typical low porosity and low permeability reservoir with an average porosity of 10.21% and an average permeability of 2.88×10-3μm2.The types of pores are inter-partical and dissolution pores with strong heterogeneity.The main diagenesis includes compaction，cementation and dissolution which belong to stage A of middle diagenesis phase according to comprehensive analysis.Original unconsolidated porosity is 35.71%.The process of pore evolution was summarized as:Strong compaction and pore reduction（-19.42%），early stage of cementation and pore reduction（-6.46%），stage of dissolution and pore increase（+3.38%） and late stage of cementation and pore reduction（-2.84%）.Also，the reduction rate of porosity by compaction is 54.38%，the reduction rate of porosity by cementation is 26.04%，and the increment rate of porosity by dissolution is 9.46%，indicating early strong compaction is the main reason of low permeability and cementation further strengthens characteristics of low permeability.


  • Productivity analysis of multifractured horizontal wells in shale gas reservoirs based on TPHM
    Jiang Rui-zhong, Yuan Jian-wei, Cui Yong-zheng, Zhang Wei, Zhang Fu-lei, Zhang Hai-tao, Mao Nian-yu
    Natural Gas Geoscience. 2019, 30(1): 95-101. https://doi.org/10.11764/j.issn.1672-1926.2018.11.011
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    Shale has complex pore structure and many micro-cracks.Traditional stress-sensitive models cannot accurately characterize the permeability changes of the shale matrix during development.Based on the Two-part Hooke's Model(TPHM)，we established a mathematical model that comprehensively considers shale gas viscous flow，Knudsen diffusion，and adsorption-desorption.We use the discrete fracture model to describe the formation micro-cracks and hydraulic fractures.The commercial software is used to solve the model by finite element method.Then we analyze the sensitivity of the corresponding parameters.The results showed that:Considering the diffusion of Knudsen，the gas production rate of shale gas increases.After considering the permeability of TPHM，the gas production rate of shale gas decreased significantly.The distance，length and number of artificial fractures have great influence on shale gas productivity.The greater the distance between artificial fractures，the larger the length and the more the number of columns，the higher the gas production rate of shale gasis.The correctness of the TPHM is verified by an example.This permeability model is more suitable for the characteristics of shale.It can more accurately simulate the productivity of shale gas wells and help develop the development plan.
  • A new calculation method for lost gas content of shale based on Arps production decline analysis model
    Zhou Shang-wen, Wang Hong-yan, Liu Hao, Guo Wei, Chen Hao
    Natural Gas Geoscience. 2019, 30(1): 102-110. https://doi.org/10.11764/j.issn.1672-1926.2018.10.021
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    Gas content is the key parameter for shale gas reservoir evaluation，and its accurate measurement is the basis for calculating geological reserves and determining development plans.In order to accurately calculate the lost gas content in shale gas field-test，the classical Arps production decline analysis method was introduced to analyze the gas content of shale，and a new method for calculating the lost gas based on this model was established.The curve of gas desorption rate decline is similar to that of gas well production decline curve.The nonlinear fitting of hyperbolic decreasing model，exponential decline model and harmonic decreasing model were applied for nonlinear fitting.Analysis results show that the fitting effect of harmonic decreasing model is poor，and the fitting effect of hyperbolic decreasing and exponential decreasing model is much better.Compared with the commonly used USBM linear method and polynomial method，it is found that the calculated results of the Arps exponential decline model are between the results of the USBM linear method and the polynomial method，and the calculation results are more accurate and reasonable.The determination of the lost time is the most important factor in the calculation of gas content.It is considered that the current method of determining the lost time is inaccurate，and it is necessary to be further studied under the actual situation of shale gas field.
  • Comprehensive seepage model of fracturing horizontal well  in shale gas reservoir considering desorption-adsorption
    Xu Chong-zhen, Zhang Gong-she, Yin Jia-wei, Ji Guo-fa, Li Xin-fa
    Natural Gas Geoscience. 2019, 30(1): 111-118. https://doi.org/10.11764/j.issn.1672-1926.2018.10.005
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    Fracturing horizontal wells are the main development mode of shale gas reservoirs.The shale gas reservoir seepage pattern is extremely complicated based on well-developed natural fractures and nano-scale pores.Therefore，it is of great significance to accurately establish the mathematical model of seepage and solve and apply it to the on-site development and production.Based on the trilinear seepage theory，the desorption-adsorption term is used to re-establish the horizontal well productivity model of shale gas reservoirs，and the bottom hole pressure formula is derived by mathematical methods such as pseudo-pressure and dimensionless and Laplace transform.Through the relationship between dimensionless production and dimensionless bottomhole pseudo-pressure，the calculation formula of shale gas horizontal well production is derived by numerical inversion.Finally，the influencing factors of gas well production are analyzed by formula and the law of single well productivity decline is verified.The results show that the derived formula can accurately calculate and predict the yield variation and capacity decline law of shale gas reservoirs，and also provide the optimal analysis conditions corresponding to the process parameters of fracturing design.
  • The characteristics of coalbed methane production and its affecting factors in Zhaozhuang field，Qinshui Basin
    Xu Yao-bo, Zhu Yu-shuang, Zhang Pei-he
    Natural Gas Geoscience. 2019, 30(1): 119-125. https://doi.org/10.11764/j.issn.1672-1926.2018.09.005
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    The 3# coal in Zhaozhuang well field in Qinshui Basin has high abundance of CBM resources.The output speed of coalbed methane desorption，diffusion and migration is slow，the exploitation of coalbed methane in this coal seam faces issues such as unstable and low production and fast decline of gas production etc.，and the exploitation of coalbed methane in this coal seam is more difficult.Therefore，according to the characteristics of the coalbed methane production，the factors influencing coalbed methane production were studied by combining experiment and field test analysis.Three affecting factors of coalbed methane production difficulties are discussed:(1)3# coal is characterized by very good development of fractures，poor fracture connectivity and filling jams.The macropore proportion of 3# coal is small and the micropore proportion is large.The seepage condition of coal seam is poor，and it has low movable fluid saturation.The drainage decompression can produce less pore fluid，and the coalbed methane output level is low.(2)The ratio between the critical desorption pressure and reservoir pressure and the gas saturation of coal seam islow，the drainage pressure drop of coalbed gas wells is small，and the expansion area of pressure drop funnel is small，resulting in poor gas production effect.(3)Coal seam has the features of strong plasticity，low stress difference  between coal seam and surrounding rock，greater extension difficulty of the fracturing fracture，easy breaking through the roof and floor for longitudinal extension，easy formation of more cracks under fracturing，limited expansion of the crack length，and poor fracturing production.It is also suggested that optimizing favorable areas for CBM development，strengthening measures for coal seam fracturing and extraction technology for sublevel fracturing horizontal wells are three favorable measures for realizing efficient CBM development in 3# coal seam in Zhaozhuang field.


  • Geochemical characteristics and reservoir forming conditions of the natural gas in the paleo central uplift zone in the northern Songliao Basin
    Zhang Fan, Ran Qing-chang, Wu Yu-ming, Ren Zhi-gao
    Natural Gas Geoscience. 2019, 30(1): 126-132. https://doi.org/10.11764/j.issn.1672-1926.2018.10.002
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    The paleo-central uplift belt in northern Songliao Basin has a low degree of exploration and weak understanding of reservoir-forming conditions，but its exploration potential cannot be ignored，and it is an important resource replacement area in the Daqing Oilfield.Based on the analysis of geochemical experimental data such as isotopes and inclusions and comprehensive geological studies，a systematic study on the geochemical characteristics and reservoir forming conditions of natural gas in the paleo-central uplift zone has been carried out for the first time.It revealed that there are no source rocks in the study area，and the gas source comes from the source rocks of Shahezi Formation.It is cleared that the initial stage of hydrocarbon generation and expulsion is the stage of reservoir formation，first filling the oil reservoir and then cracked into gas reservoir.It is pointed out that the bedrock in the paleo-central uplift zone is the predominant area for hydrocarbon migration and accumulation，and possesses the conditions for gas accumulation，which can be used as the key area for next step deep gas exploration in Songliao Basin.
  • Geochemical features of hydrocarbon gas generated from different coaly source rocks by pyrolysis experiments：Case study of the Sulige Gas Field in the Ordos Basin，China
    Yu Cong, Hu Guo-yi, Chen Rui-yin
    Natural Gas Geoscience. 2019, 30(1): 133-142. https://doi.org/10.11764/j.issn.1672-1926.2018.10.025
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    In order to study the gas generation process of different coaly source rocks，we did thermal simulation experiments on coal，coaly mudstone and carbon mudstone.And a series of geochemical analysis including chemical composition，carbon and hydrogen isotope composition as well as light hydrocarbon analysis on thermal simulation gas are also carried out in this study.It revealed coal has the highest gas production rate，in addition，it yields a large amount of CO2 gas in the early stage of simulation experiment.Carbon and hydrogen isotope of coalthermal simulation gas is slightly heavier than that of coaly mudstone and carbonaceous mudstone gas.Before 500℃，carbon and hydrogen isotope of these three kinds of gases became lighter and then higher with the increase of temperature，but after 500℃，they became lighter all the time.Carbon isotope series reversal is observed in this process.The coal thermal simulation gas has the highest content of benzene，toluene and 2，3-methyl pentane.This study indicated 2 high lights on Sulige Gas Field:(1) CO2，formed in the early stage of hydrocarbon generation，may have a direct relationship with reservoir densification in the Sulige Gas Field.(2) According to the analysis of light hydrocarbon，coal should be the dominant contributor for the accumulation of the Sulige natural gas，but the contribution of coaly mudstone and carbonaceous mudstone cannot be ignored.
  • Geochemical characteristics of rare earth elements in karst reservoirs in  Maokou Formation，northern Guizhou Province
    Wang Shuai, Wang Gan-lu, Qin Zheng, Gao Ze-yuan, Luo Teng
    Natural Gas Geoscience. 2019, 30(1): 143-150. https://doi.org/10.11764/j.issn.1672-1926.2018.08.018
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    The experiment and analysis of REE were carried out on the rock samples of the Maokou Formation in northern Guizhou Province.The study showed that the REE value of the ancient karst rock samples in the northern Guizhou Province was (4.08-23.04)×10-6，with an average of 9.21×10-6，showing slightly right-diagonal REE pattern.The parameters of (La/Yb)N-∑REE show that with the progress of karstification，the enrichment of rare earth elements will decrease.The karst rocks of various genetic types have the feature that the migration rate of light rare earth elements is higher than that of heavy rare earth elements，and the differentiation of light and heavy rare earth elements will become more apparent;the δCe value of rock samples is 0.71-0.98，with an average of 0.85.The value of δEu is 0.55-0.93 and the average value is 0.69.The anomaly of Ce is much worse than that of Eu，indicating that the paleo-karst reservoirs in the northern part of Guizhou were mainly formed in the oxidative flow environment of the seepage-active subduction zone.
  • Natural Gas geoscience 2019-1 covers and titles
    Natural Gas Geoscience. 2019, 30(1): 9011-9022.
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    《天然气地球科学》2019-1期封面及目次
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