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891.
In this paper orientations of quartz veins from the Archaean age lode-gold bearing region of Gadag (southern India) are used to determine the relative stress and fluid pressure (Pf) conditions by constructing 3-D Mohr circle. Anisotropy of magnetic susceptibility (AMS) analysis of the host massive metabasalt reveals that the magnetic foliation is NW–SE striking, which is related to early NE–SW compression (D1/D2 deformation) that affected the region. The quartz veins have a wide range of orientations, with NW–SE striking veins (steep northeasterly dips) being the most prominent. Vein emplacement is inferred to have taken place under NW–SE compression that is known to have caused late deformation (D3) in the region. It is argued that the NW–SE fabric defined the pre-existing anisotropy and channelized fluid flow during D3. The permeability was initially low, which resulted in high Pf (>σ2). 3-D Mohr circle analysis indicates that the driving pressure ratio (R′) was 0.94, a condition that favoured fracturing and reactivation of fabric elements (foliations and fractures) having a wide range of orientations. This led to an increase in permeability and fluid flowed (burped) into the fractures. Resulting vein emplacement and sealing of fractures led to a reduction of Pf (<σ2). It is argued that at this low Pf, NW–SE oriented structures continued to remain susceptible to reactivation and vein emplacement, while fractures of all other orientations were inactive and remained sealed. As a consequence, the study area has a cluster of NW–SE oriented veins. R′ is calculated to be 0.07 from 3-D Mohr circle analysis at low Pf, when fractures with NW–SE orientation only were susceptible to dilation. However, it is envisaged that any emplacement of veins in these fractures would have sealed them, thus reducing the permeability and initiating the next cycle of rise in Pf (>σ2). Thus, it is concluded that the quartz veins in the Gadag region are a consequence of an interplay between conditions that fluctuated from Pf > σ2 to Pf < σ2. 相似文献
892.
合肥盆地中南部肥西县磨墩水库南岸防虎山组侏罗系砾岩下发育一套石墨片岩系,两者之间呈断层接触.该石墨片岩不同于钻井揭示的合肥盆地石炭纪一二叠纪沉积岩,亦不同于河南固始县杨山煤系.经分析认为该石墨片岩应属于北淮阳佛子岭群岩系,原岩为炭质泥岩或炭质粉砂岩.石墨为有机成因,石墨化程度较低,但变形强烈,部分已糜棱岩—超糜棱岩,反映出俯冲—碰撞带变形变质特征.通过对白云母、石墨XRD衍射和电子探针测试分析,认为石墨片岩为绿片岩相,估算其变质温度为450~ 500℃,压力0.55 ~0.8GPa.根据显微构造特征和变形—变质条件推断,该石墨片岩为扬子板块北缘的沉积盖层(佛子岭群部分),在扬子板块与华北板块碰撞过程中受到强烈挤压,变形—变质成糜棱岩、石墨构造片岩.该变形带暗示了扬子板块向华北板块缝合带的位置,即石墨片岩出露区及其附近,部分被新生代沉积所覆盖. 相似文献
893.
C. M. Aruffo A. Rodriguez-herrera E. Tenthorey F. Krzikalla J. Minton A. Henk 《Australian Journal of Earth Sciences》2013,60(7):987-1001
This paper presents the first published 3D geomechanical modelling study of the CO2CRC Otway Project, located in the state of Victoria, Australia. The results of this work contribute to one of the main objectives of the CO2CRC, which is to demonstrate the feasibility of CO2 storage in a depleted gas reservoir. With this aim in mind, a one-way coupled flow and geomechanics model is presented, with the capability of predicting changes to the in situ stress field caused by changes in reservoir pressure owing to CO2 production and injection. A parametric study investigating the pore pressures required to reactivate key, reservoir-bounding faults has been conducted, and the results from the numerical simulation and analytical analysis are compared. The numerical simulation indicates that the critical pore fluid pressure to cause fault reactivation is 1.15 times the original pressure as opposed to 1.5 times for the comparable analytical model. Possible reasons for the differences between the numerical and analytical models can be ascribed to the higher degree of complexity incorporated in the numerical model. Heterogeneity in terms of lateral variations of hydrological and mechanical parameters, effect of topography, presence of faults and interaction between cells are considered to be the main sources for the different estimation of critical pore pressure. The numerical model, which incorporates this greater complexity, is able then to better describe the state of stress that acts in the subsurface compared with a simple 1D analytical model. Moreover, the reactivation pressures depend mainly on the state of stress described; therefore we suggest that numerical models be performed when possible. 相似文献
894.
针对巨厚松散层在钻孔施工中易出现钻孔孔壁坍塌、掉块、缩径,造成埋钻、粘钻、卡钻,找不到原孔而形成岔孔等钻孔事故,简述了在巨厚松散层钻孔裸孔安全施工的要点和注意事项。 相似文献
895.
《Geomechanics and Geoengineering》2013,8(3):218-229
ABSTRACTThe present study deals with the determination of passive earth pressure under seismic condition by following the lower bound finite elements limit analysis and modified pseudo-dynamic methodology. In accordance with the lower bound finite elements formulation, the stress field was modelled using a three-noded triangular elements, while the passive pressure was determined via linear optimisation. The parametric study was performed, for a vertical rigid retaining wall, by varying the magnitude of seismic acceleration in horizontal direction (kh) between 0 and 0.3, while the vertical seismic acceleration (kv) was kept equal to 0 or 0.5 kh. Furthermore, the damping coefficient for dry cohesionless backfill was kept ξ = 10%. The obtained results in various cases were found to be in good agreement with those found in the literature. It is expected that this method can be further used for solving other important geotechnical stability problems. 相似文献
896.
《Geomechanics and Geoengineering》2013,8(4):237-245
The increasing use of backfill in underground mines requires a proper evaluation of the stress state in and around the filled openings. This is, however, a relatively complex issue due, in part, to the large contrast in strength and stiffness between the backfill material and surrounding rock mass. In recent years, it has been shown that arching theory, based on limit equilibrium analysis, can be used to estimate the stress distribution in backfilled stopes. Nonetheless, many simplifications are involved in such analytical solutions and this affects the precision and significance of the calculated results. In this paper, a previously developed solution is enhanced by introducing the combined effects of non-uniform vertical stress distribution and positive pore water pressure. This leads to a more representative analytical solution, as demonstrated by successful comparisons with numerical simulations. The results indicate that the proposed solution can be used to estimate the effective and total stress state in submerged or partially submerged backfilled stopes with a simple geometry. 相似文献
897.
塔里木盆地凝析气田的地质特征及其形成机制 总被引:2,自引:0,他引:2
塔里木盆地凝析油气资源丰富,已发现了二十余个凝析气田,包括库车坳陷的陆相油气来源的凝析气田和台盆区海相烃源岩来源的凝析气田;储层有碎屑岩,也有碳酸盐岩;时代自奥陶系至新生代均有分布。这些凝析气田的气油比分布在600~19900m3/m3,凝析油含量40~750g/m3;储层温度在78~155℃;地层压力在37~111MPa。研究认为,塔里木盆地凝析气藏的成因类型可以分为原生凝析气藏和次生凝析气藏。其中,以库车坳陷迪那2凝析气田为代表的煤系烃源岩在高演化阶段(镜质体反射率Ro为1.2%~2.0%),即凝析油和湿气生成带所形成的原生腐植型凝析气藏或煤成型凝析气藏。次生凝析气藏包括两类:陆相油气来源的多期充注,晚期干气对早期油藏发生混合改造,形成了以牙哈为代表的陆相油气成因的次生凝析气藏;以海相油气来源,多期油气充注与晚期干气气侵,造成蒸发分馏,在运移、聚集和成藏过程中烃体系分异、富化,发生反凝析作用,从而导致次生凝析气藏的形成。随着塔里木盆地勘探向深层转化,地层的温度和压力逐渐增高,烃类演化程度的升高,不同生烃阶段的烃体系混合也将更为普遍,次生凝析气藏也将更为普遍,因此,以海相油气来源的次生成因型凝析气藏将成为勘探的主体。 相似文献
898.
899.
900.