Natural fractures within unconventional reservoirs of Linxing Block, eastern Ordos Basin, central China

Abstract

Unconventional reservoirs are generally characterized by low matrix porosity and permeability, in which natural fractures are important factors for gas production. In this study, we analyzed characteristics of natural fractures, and their influencing factors based on observations from outcrops, cores and image logs. The orientations of natural fractures were mainly in the ~N-S, WNW-ESE and NE-SW directions with relatively high fracture dip angles. Fracture densities were calculated based on fracture measurements within cores, indicating that natural fractures were not well-developed in the Benxi-Upper Shihezi Formations of Linxing Block. The majority of natural fractures were open fractures and unfilled. According to the characteristics of fracture sets and tectonic evolution of the study area, natural fractures in the Linxing Block were mainly formed in the Yanshanian and Himalayan periods. The lithology and layer thickness influenced the development of natural fractures, and more natural fractures were generated in carbonate rocks and thin layers in the study area. In addition, in the Linxing Block, natural fractures with ~N-S-trending strikes contributed little to the overall subsurface fluid flow under the present-day stress state. These study results provide a geological basis for gas exploration and development in the Linxing unconventional reservoirs of Ordos Basin.

Keywords

natural fracture / unconventional reservoir / Linxing region / influencing factors / Ordos Basin

References

[1] Aadnoy B S, Bell J S (1998). Classification of drilling-induced fractures and their relationship to in-situ stress directions. Log Anal, 39(6): 27–42

[2] Aydin A (2000). Fractures, faults, and hydrocarbon entrapment, migration, and flow. Mar Pet Geol, 17(7): 797–814

[3] Bhandakkar P, Siddhamshetty P, Sang-Il Kwon J (2020). Numerical study of the effect of propped surface area and fracture conductivity on shale gas production: application for multi-size proppant pumping schedule design. J Nat Gas Sci Eng, 79: 103349

[4] Bowker K A (2007). Barnett shale gas production, Fort Worth Basin: issues and discussion. AAPG Bull, 91(4): 523–533

[5] Buller D, Hughes S N, Market J, Petre J E, Spain D R, Odumosu T (2010). Petrophysical evaluation for enhancing hydraulic stimulation in horizontal shale gas wells. Society of Petroleum Engineers

[6] Canady W, Market J, (2008). Fracture characterization by borehole logging methods. Society of Petrophysicists and Well-Log Analysts, SPWLA-2008-AAA (1–12)

[7] Dahi-Taleghani A, Olson J E (2011). Numerical modeling of multistranded-hydraulic-fracture propagation: accounting for the interaction between induced and natural fractures. Society of Petroleum Engineers, 16(3): 575–581

[8] Folkestad A, Veselovsky Z, Roberts P (2012). Utilising borehole image logs to interpret delta to estuarine system: a case study of the subsurface Lower Jurassic Cook Formation in the Norwegian northern North Sea. Mar Pet Geol, 29(1): 255–275

[9] Fossen H (2010). Structural Geology. Cambridge: Cambridge University Press

[10] Gale J F W, Laubach S E, Olson J E, Eichhuble P, Fall A (2014). Natural fractures in shale: a review and new observations. AAPG Bull, 98(11): 2165–2216

[11] Gale J F W, Reed R M, Holder J (2007). Natural fractures in the Barnett Shale and their importance for hydraulic fracture treatments. AAPG Bull, 91(4): 603–622

[12] Gao X D, Wang Y B, Ni X M, Li Y, Wu X, Zhao S H, Yu Y (2018). Recovery of tectonic traces and its influence on coalbed methane reservoirs: a case study in the Linxing area, eastern Ordos Basin, China. J Nat Gas Sci Eng, 56: 414–427

[13] Hall S A, Kendall J M, Barkved O I (2002). Fractured reservoir characterization using P-wave AVOA analysis of 3D OBC data. Leading Edge (Tulsa Okla), 21(8): 777–781

[14] Hancock P L (1985). Brittle microtectonics: principles and practice. J Struct Geol, 7(3–4): 437–457

[15] Harstad H, Teufel L W, Lorenz J C (1995). Characterization and simulation of naturally fractured tight gas sandstones. Society of Petroleum Engineers

[16] Hennings P H, Olson J E, Thompson L B (2000). Combining outcrop data and three-dimensional structural models to characterize fractured reservoir: an example from Wyoming. AAPG Bull, 84: 830–849

[17] Ju W, Niu X B, Feng S B, You Y, Xu K, Wang G, Xu H R (2020). Present-day in-situ stress field within the Yanchang Formation tight oil reservoir of Ordos Basin, central China. J Petrol Sci Eng, 187: 106809

[18] Ju W, Shen J, Qin Y, Meng S Z, Wu C F, Shen Y L, Yang Z B, Li G Z, Li C (2017). In-situ stress state in the Linxing region, eastern Ordos Basin, China: implications for unconventional gas exploration and production. Mar Pet Geol, 86: 66–78

[19] Ju W, Sun W F (2016). Tectonic fractures in the Lower Cretaceous Xiagou Formation of Qingxi Oldfield, Jiuxi Basin, NW China. Part one: characteristics and controlling factors. J Petrol Sci Eng, 146: 617–625

[20] Ju W, Sun W F, Hou G T (2015). Insights into the tectonic fractures in the Yanchang Formation interbedded sandstone-mudstone of the Ordos Basin based on core data and geomechanical models. Acta Geol Sin, 89(6): 1986–1997

[21] Ju W, Wang J L, Fang H H, Sun W F (2019). Paleotectonic stress field modeling and prediction of natural fractures in the Lower Silurian Longmaxi shale reservoirs, Nanchuan region, South China. Mar Pet Geol, 100: 20–30

[22] Ju W, Wang K, Hou G T, Sun W F, Yu X (2018). Prediction of natural fractures in the Lower Jurassic Ahe Formation of the Dibei Gasfield, Kuqa Depression, Tarim Basin, NW China. Geosci J, 22(2): 241–252

[23] Laubach S E, Marrett R A, Olson J E, Scott A R (1998). Characteristics and origins of coal cleat: a review. Int J Coal Geol, 35(1–4): 175–207

[24] Laubach S E, Olson J E, Gross M R (2009). Mechanical and fracture stratigraphy. AAPG Bull, 93(11): 1413–1426

[25] Li Y, Tang D Z, Wu P, Niu X L, Wang K, Qiao P, Wang Z S (2016). Continuous unconventional natural gas accumulation of Carboniferous-Permian coal-bearing strata in the Linxing area, northeastern Ordos Basin, China. J Nat Gas Sci Eng, 36: 314–327

[26] Liu C Y, Zhao H G, Sun Y Z (2009). Tectonic background of Ordos Basin and its controlling role for basin evolution and energy mineral deposits. Energy Exploration and Exploitation, 27(1): 15–27

[27] Marrett R, Ortega O J, Kelsey C M (1999). Extent of power-law scaling for natural fractures in rock. Geology, 27(9): 799–802

[28] McGinnis R N, Ferrill D A, Morris A P, Smart K J, Lehrmann D (2017). Mechanical stratigraphic controls on natural fracture spacing and penetration. J Struct Geol, 95: 160–170

[29] Narr W (1991). Fracture density in the deep subsurface: techniques with application to Point Arguello Oil Field. AAPG Bull, 75: 1300–1323

[30] Narr W, Suppe J (1991). Joint spacing in sedimentary rocks. J Struct Geol, 13(9): 1037–1048

[31] Nelson R A (2001). Geologic Analysis of Naturally Fractured Reservoirs. 2nd ed. Massachusetts: Gulf Professional Publishing

[32] Olson J E, Laubach S E, Lander R H (2009). Natural fracture characterization in tight gas sandstones: integrating mechanics and diagenesis. AAPG Bull, 93(11): 1535–1549

[33] Qu H Z, Zhang F X, Wang Z Y, Yang X T, Liu H T, Ba D, Wang X (2016). Quantitative fracture evaluation method based on core-image logging: a case study of Cretaceous Bashijiqike Formation in ks2 well area, Kuqa depression, Tarim Basin, NW China. Pet Explor Dev, 43(3): 465–473

[34] Rajabi M, Sherkati S, Bohloli B, Tingay M (2010). Subsurface fracture analysis and determination of in-situ stress direction using FMI logs: an example from the Santonian carbonates (Ilam Formation) in the Abadan Plain, Iran. Tectonophysics, 492(1–4): 192–200

[35] Sibson R H (1996). Structural permeability of fluid-driven fault-fracture meshes. J Struct Geol, 18(8): 1031–1042

[36] Shen J, Qin Y, Zhang B, Li G Z, Shen Y L (2018). Superimposing gas-bearing system in coal measures and its compatibility in Linxing block, east Ordos Basin. Journal of China Coal Society, 43(6): 1614–1619 (in Chinese)

[37] Shen Y L, Qin Y, Wang G, Guo Y H, Shen J, Gu J Y, Xiao Q, Zhang T, Zhang C L, Tong G C (2017). Sedimentary control on the formation of a multi-superimposed gas system in the development of key layers in the sequence framework. Mar Pet Geol, 88: 268–281

[38] Shu Y, Lin Y X, Liu Y, Yu Z Y (2019). Control of magmatism on gas accumulation in Linxing area, Ordos Basin, NW China: evidence from fluid inclusions. J Petrol Sci Eng, 180: 1077–1087

[39] Siddhamshetty P, Bhandakkar P, Kwon J S (2020). Enhancing total fracture surface area in naturally fractured unconventional reservoirs via model predictive control. J Petrol Sci Eng, 184: 106525

[40] Speight J G (2019). Natural Gas: A Basin Handbook. 2nd ed. Massachusetts: Gulf Professional Publishing

[41] Tingay M, Reinecker J, Muller B, (2008). Borehole breakout and drilling-induced fracture analysis from image logs. World Stress Map Project Guidelines: Image Logs, 1–8

[42] van Golf-Racht T D (1982). Fundamentals of Fractured Reservoir Engineering. New York: Elsevier Scientific Publishing Company

[43] Wang X Y, Zhang Q L, Wang L S, Ge R F, Chen J (2010). Structural features and tectonic stress fields of the Mesozoic and Cenozoic in the eastern margin of the Ordos Basin. Geological Bulletin of China, 29(8): 1168–1176 (in Chinese)

[44] Wang Y C (1992). Fractured Tight Oil and Gas Reservoirs. Beijing: Geological Publishing House

[45] Weniger S, Weniger P, Littke R (2016). Characterizing coal cleats from optical measurements for CBM evaluation. Int J Coal Geol, (154–155): 176–192

[46] Wu K, Olson J E (2016). Numerical investigation of complex hydraulic-fracture development in naturally fractured reservoirs. SPE Prod Oper, 31(4): 300

[47] Xie Y G, Sun X Y, Wan H, Duan C J, Chen Q, Yu Y J (2017). A study of shallow-water deltaic facies from Upper Shihezi Formation in Linxing area, Ordos Basin. Unconventional Oil and Gas, 4(2): 13–21 (in Chinese)

[48] Yang Y T, Li W, Ma L (2005). Tectonic and stratigraphic controls of hydrocarbon systems in the Ordos Basin: a multicycle cratonic basin in central China. AAPG Bull, 89(2): 255–269

[49] Zeng L B (2008). Formation and Distribution of Natural Fractures in Low-permeability Sandstone Reservoirs. Beijing: Science Press (in Chinese)

[50] Zeng L B, Li X Y (2009). Fractures in sandstone reservoirs with ultra-low permeability: a case study of the Upper Triassic Yanchang Formation in the Ordos Basin, China. AAPG Bull, 93(4): 461–477

[51] Zhao G C, Sun M, Wilde S A, Li S Z (2005). Late Archean to Paleoproterozoic evolution of the North China Craton: key issues revisited. Precambrian Res, 136(2): 177–202

[52] Zhao M W, Hans J B, Hans A (1996). Thermal and tectonic history of the Ordos Basin, China: Evidence from apatite fission track analysis, vitrinite reflectance, and K-Ar dating. AAPG Bull, 80(7): 1110–1134

[53] Zoback M D, Barton C A, Brudy M, Castillo D A, Finkbeiner T, Grollimund B R, Moos D B, Peska P, Ward C D, Wiprut D J (2003). Determination of stress orientation and magnitude in deep wells. Int J Rock Mech Min Sci, 40(7–8): 1049–1076

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