沁水盆地南部高角度正断层区应力莫尔圆及包络线分析
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摘要
受主断裂的影响,断裂发育地区地层岩石中通常发育一系列伴生小断层及裂缝,岩石的莫尔圆及包络线均会呈现不同的变化规律。沁水盆地南部上古生界地层中高角度及近垂直正断层极为发育,通过设计三轴应力测试实验,对高角度正断层区进行了应力莫尔圆及包络线分析。研究结果表明,与远离断层的结构完整岩石相比,正断层区的莫尔圆会向左移动,同时半径减小,其断面倾角(θ_1)较大,与该地区上古生界地层广泛发育高角度及近垂直正断层结果一致。对于同一应力机制条件下的正断层,θ_1不随深度而发生变化。断层薄弱带为高角度正断层产生过程中形成的一些次级小断层或裂缝发育带,岩心观察表现为破碎带,其成层性分布角度通常小于30°,其与莫尔圆中较低的断层薄弱带倾角(θ_2)一致。随着正断层断面倾角的增加,地层岩石的抗剪切破裂的强度逐渐提高。
In the area of fracture development, influenced by the main fracture, a series of associated small faults and fractures are usually developed in stratigraphic rocks, and the Mohr's circle and envelope lines of rocks usually show different change regularities. The high-angle and near-vertical normal faults in the upper Paleozoic strata in the south of Qinshui basin are extremely developed. The research results show that,compared with the structurally intact rocks that are far away from the fault, the Mohr's circle of the normal fault disk moves to the left, its radius decreases at the same time, and its cross section angle(θ_1) is larger,which is consistent with the results that high angle normal faults are developed. For the normal faults under the same stress mechanism, θ_1 value does not change with the depth. In weak fault zone, there are some secondary small faults, or fractures formed after the high angle normal fault zones are formed, which are fractured zones from the core observation, its layer distribution angle is usually less than 30 °, and it is consistent with the lower weak fault belt angle(θ_2) in the Mohr's circle. With the increase of the normal fault dip angle, the shear resistance strength of rocks will increase gradually.
In the area of fracture development, influenced by the main fracture, a series of associated small faults and fractures are usually developed in stratigraphic rocks, and the Mohr's circle and envelope lines of rocks usually show different change regularities. The high-angle and near-vertical normal faults in the upper Paleozoic strata in the south of Qinshui basin are extremely developed. The research results show that,compared with the structurally intact rocks that are far away from the fault, the Mohr's circle of the normal fault disk moves to the left, its radius decreases at the same time, and its cross section angle(θ_1) is larger,which is consistent with the results that high angle normal faults are developed. For the normal faults under the same stress mechanism, θ_1 value does not change with the depth. In weak fault zone, there are some secondary small faults, or fractures formed after the high angle normal fault zones are formed, which are fractured zones from the core observation, its layer distribution angle is usually less than 30 °, and it is consistent with the lower weak fault belt angle(θ_2) in the Mohr's circle. With the increase of the normal fault dip angle, the shear resistance strength of rocks will increase gradually.
引文
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[3]李海,郭召杰,刘瑞珣,等.极莫尔圆在测量有体积变化剪切带剪切位移量中的应用[J].中国科学(D辑),2000,30(4):192–298.
[4]BOZKURT E,SOZBILIR H.Tectonic evolution of the Gediz Graben:field evidence for an episodic,two–stage extension in western Turkey[J].Geological Magazine,2004,141(1):63–79.
[5]MORRISA,FERRILLDA,HENDERSONDB.Slip–tendency analysis and fault reactivation[J].Geology,1996,24(3):275–278.
[6]GIGER S B,COX S F,TENTHOREY E.Slip localization and fault weakening as a consequence of fault gouge strengthening Insights from laboratory experiments[J].Earth and Planetary Science Letters,2008,276(1–2):73–84.
[7]秦勇,梁建设,申建,等.沁水盆地南部致密砂岩和页岩的气测显示与气藏类型[J].煤炭学报,2014,39(8):1 559–1 565.
[8]梁建设,王存武,柳迎红,等.沁水盆地致密气成藏条件与勘探潜力研究[J].天然气地球科学,2015,25(10):1 509–1 517.
[9]BRAUNMILLER J,NABELEK J.Geometry of continental normal faults[J].Journal of Geophysical Research,1996,101(B2):3 045–3 052.
[10]HORINO F G,ELLICKSON M L.A method of estimating strength of rock containing planes of weakness[C].U.S.Bureau of Mines Report of Investigations,1970,7 447–7 449.
[11]BAGHERIPOURMH, MOSTYNGR. Predictionof strength of jointed rock:theory and practice[M].In Proceedings of ISRM International Symposiu(Eurock’96),Torino,Italy,1996,231–238.
[12]MCLAMORE R,GRAY K E.The mechanical behavior of anisotropic sedimentary rocks[J].Journal of Engineering for Industry 1967,89(1):62–72.
[13]SU Xianbo,LIN Xiaoying,ZHAO Mengjun,et al.The upper Paleozoic coalbed methane system in the Qinshui Basin,China[J].AAPG Bulletin,2005,89(1):81–100.