تحلیل میدان تنش و فشار منفذی با استفاده از بررسی هندسی رگه¬های ژیپسی در تاقدیس میدان نفتی نفت سفید، جنوب باختر ایران
محورهای موضوعی : شاخه های دیگر علوم زمین در ارتباط با زمین شناسی نفت
1 - دانشکده علوم زمین دانشگاه شهید چمران اهواز
کلید واژه: رگههای ژیپسی, فشار منفذی, میدان تنش, تاقدیس نفت سفید, سازند گچساران, کمربند چین خورده-رانده زاگرس,
چکیده مقاله :
در این پژوهش، از رگههای ژیپسی موجود در واحدهای سنگی سازند گچساران در تاقدیس نفت سفید بهعنوان شاخصهای مؤثر در تعیین راستای محورهای اصلی تنش و مقادیر نسبی فشار منفذی و تنش های اصلی استفاده شده است. بدین منظور تحلیل هندسی رگهها با بهکارگیری دادههای استریوگرافی قطب رگهها و ترسیم نمودار مور صورت پذیرفت. نتایج حاصل نشان میدهد که پراکندگی گسترده قطب رگههای ژیپسی بیانگر غلبه فشار منفذی نسبت به تنش میانگین (Pf > σ₂) در زمان تشکیل آنها بوده است. تحلیلهای ساختاری نشان داد که محور تنش بیشینه (σ1) دارای راستای شمالباختری–جنوبخاوری است که با جهت عمومی رژیم فشارشی در کمربند چینخورده و رانده زاگرس مطابقت دارد. مقادیر نسبت فشار محرک (R′) در بازهی 0.73 تا 0.84 و فشار منفذی در حدود 4004 تا 4581 واحد برآورد گردید. همچنین مقدار نسبت تنش (Ø=0.81) بدست آمده بیانگر شرايط بيضوي تنش فشرده سه محوري در زمان تشکیل رگههای ژیپسی است. نتایج این مطالعه بیانگر نقش مستقیم میدان تنش و فشار سیالات در کنترل توسعه رگهها در سنگهای گچی سازند گچساران میباشد.
In this study, gypsum veins occurring within the Gachsaran Formation of the Naft Sefid Anticline were employed as structural indicators to determine the orientation of the principal stress axes and to estimate the relative magnitudes of the principal stresses and pore pressure. For this purpose, Stereographic analysis of the veins pole data and Mohr diagram construction were performed. The results indicate that the wide dispersion of gypsum vein poles reflects the dominance of pore pressure over the mean stress (Pf > σ₂) during vein formation. Structural analysis revealed that the maximum principal stress axis (σ₁) trends northwest–southeast, consistent with the general compressional regime of the Zagros fold-and-thrust belt. The calculated driving pressure ratio (R′) ranges between 0.73 and 0.84, and pore pressure values vary from 4004 to 4571 units. The stress ratio (Ø = 0.81) indicating three axial oblate shape of stress ellipsoid during the development of gypsum veins. These results highlight the significant influence of stress field orientation and fluid pressure on vein development within the Gachsaran Formation.
[1] ALAVI, M., 2007. Structures of the zagros fold-thrust belt in Iran. American Journal of Science, 307, 1064–1095.
[2] ANGELIER, J., 1984. Tectonic analysis of fault slip data sets. Journal of Geophysics Researches, 89, 5835–5848.
[3] BEAR, G., BEYTH, M., RECHES, Z., 1994. Dike emplaced into fractured basement, Timna Igneous Complex, Israel. Journal of Geophysics Researches, 99, 24039–24051.
[4] BERBERIAN, M., 1995. Master ‘blind’ thrust faults hidden under the Zagros folds: active basement tectonics and surface morphotectonics. Tectonophysics, 241, 193–224.
[5] BERBERIAN, M., KING, G.C.P., 1981. Towards a paleogeography and tectonic evolution of Iran. Canadian Journal of Earth Sciences, 18, 210–265.
[6] BLANCE, E.J.P., ALLEN, M.B., INGER, S., HASSANI, H., 2003. Structural styles in the Zagros Simple Folded Zone, Iran. Journal of the Geological Society, 160, 401–412. doi:10.1144/0016-764902-110.
[7] BORDENAVE, M. L., HEGRE, J. A., 2005. The influence of tectonics on the entrapment of oil in the Dezful Embayment, Zagros Foldbelt, Iran. Journal of Petroleum Geology, 28(4), 339–368.
[8] FAGHIH, A., DEHGHAN M., SOBHANI S.S., 2023. Study of deformation pattern and kinematic characteristics in the Gelmandeh metamorphic complex, Saghand region, Central Iran. Advanced Applied Geology, 12(4), 617–634.
[9] FALCON, N.L., 1974. Problems of the relationship between surface structures and deep displacements illustrated by the Zagros range. Geological Society of London. Special Publication, 3, 9–22.
[10] FERGOSSON, C., NUTMAN, A., MOHAJJEL, M., BENNETT, V.C., 2016. The Sanandaj–Sirjan Zone in the Neo-Tethyan suture, western Iran: Zircon U–Pb evidence of late Paleozoic rifting of northern Gondwana and mid-Jurassic orogenesis. Gondwana Research, 58, 216–238.
[11] FOSSEN, H., 2016. Structural geology (2nd ed.). Cambridge University Press
[12] JOLLY, R.J.H., SANDERSON, D.J., 1997. A Mohr circle reconstruction for the opening of a pre-existing fracture. Journal of Structural Geology, 19, 887–892.
[13] KESHAVARZ, S., FAGHIH, A., ASADI, S., SOLEIMANI, M., ZAREI, S., 2024. PT conditions of deformation of the Gol-e-Gohar shear zone, SW Iran: Insights from analysis of quartz c-axis fabrics, recrystallization mechanisms and syndeformational fluid inclusions. Journal of Asian Earth Sciences, 262, 106010.
[14] KRUHL, J.H., 1998. Reply: prism- and basal-plane parallel subgrain boundaries in quartz: a microstructural geothermobarometer. Journal of Metamorphic Geology, 16, 142–146.
[15] LAW, R.D., 1990. Crystallographic fabrics. A selective review of their applications to research in structural geology. In: Knipe, R.J., Rutter, E.H. (Eds.), Deformation Mechanisms, Rheology and Tectonics. Geological Society of London, Special Publication No. 54, pp. 335–52.
[16] LAW, R.D., SEARLE, M.P., SIMPSON, R.L., 2004. Strain, deformation temperatures and vorticity of flow at the top of the Greater Himalayan Slab, Everest Massif. Tibet. Journal of Geological Society, London, 161, 305–320.
[17] MCKEAGNEY, C.J., BOULTER, C.A., JOLLY, R.J.H., FOSTER, R.P., 2004. 3D Mohr Circle analysis of vein opening, Indrama lode-gold deposit, Zimbabwe: implication for exploration. Journal of Structural Geology, 26, 1275–1291.
[18] MCQUARRIE, N., 2004. Crustal scale geometry of the Zagros fold–thrust belt, Iran. Journal of Structural Geology, 26, 519–535.
[19] MOHAJJEL, M., FERGUSSON, C.L., 2000. Dextral transpression in Late Cretaceous continental collision, Sanandaj–Sirjan Zone, western Iran. Journal of Structural Geology, 22, 1125–1139.
[20] NÜCHTER, J.A., STÖCKHERT, B., 2008. Coupled stress and pore fluid pressure changes in the middle crust: Vein record of coseismic loading and postseismic stress relaxation. Tectonics, 27, 1–23.
[21] OTSUBO, M., MIYAKAWA, A., KAWASAKI, R., SATO, K., YAMAGUCHI, A., KIMURA, A., 2016. Variations in stress and driving pore fluid pressure ratio using vein orientations along megasplay faults: Example from the Nobeoka Thrust, Southwest Japan. Island Arc, 25, 421–432.
[22] SADEGHI, S., YASSAGHI, A., 2016. Spatial evolution of Zagros collision zone in Kurdistan, NW Iran: Constraints on Arabia–Eurasia oblique convergence. Solid Earth, 7, 659–672. doi:10.5194/se-7-659-2016.
[23] SAEDI, G., SOLEIMANI, B., SAMANI, B., ARZANI, A., 2022. The interaction between faults and in-situ stress on the kinematic and subsurface natural fracture of Aghajari oilfield in southwest of Iran. Journal of Petroleum Science and Engineering, 208, 109567.
[24] SAMANI, B., 2017. Deformation flow analysis and symmetry of Goushti shear zone, Sanandaj-Sirjan metamorphic belt, Iran. Geopersia, 7, 117-130.
[25] SARKARINEJAD, K., AZIZI, A., 2008. Slip partitioning and inclined dextral transpression along the Zagros Thrust System, Iran. Journal of Structural Geology, 30, 116–136.
[26] SARKARINEJAD, K., KESHAVARZ, S., FAFGIH, A., SAMANI, B., 2017. Kinematic analysis of rock flow and deformation temperature of the Sirjan thrust sheet, Zagros Orogen, Iran. Geological Magazine, 154, 147–165.
[27] SCHWARZHANS, W., Bosold, A., JULAPOUR, A., ASHRAFZADEH, A.R., EHSANI, S.M., 2025. The structural geology of the High Central Zagros revisited (Iran) Available to Purchase. Petroleum Geoscience (2005) 11 (3): 225–238.
[28] SEMBRONI, A., Riccardo REITANO, A., FACCENNA, C., CALLIERI, P, 2024. The geologic configuration of the Zagros Fold and Thrust Belt: an overview. Mediterranean Geoscience Reviews, 6:61–86
[29] SEPEHR, M., COSGROVE, J., MOINEI, M., 2006. The impact of cover rock rheology on the style of folding in the Zagros fold-thrust belt. Tectonophysics, 427(1-4), 265-281.
[30] STOCKLIN, J., 1968. Structural history and tectonics of Iran, a review, A. A. P. G. Bull., 52(7), 1229-1258.
[31] TAKIN, M., 1972. Iranian geology and continental drift in the Middle East. Nature, 235, 147-150.
[32] TALEBIAN, M., JACKSON, J., 2004. A reappraisal of earthquake focal mechanisms and active shortening in the Zagros mountains of Iran. Geophysics, 156, 506–526.
[33] WILSON, C.J.L., ROBINSON, J.A., DUGDALE, A.L., 2008. Quartz vein fabrics coupled to elevated fluid pressures in the Stawell gold deposit, south-eastern Australia. Mineralium Deposita, 44(2):245-263.
[34] ZAMANI, B.G, 2023. Geodynamics and tectonic stress model for the Zagros fold–thrust belt and classification of tectonic stress regimes. Marine and Petroleum Geology, 155, 1-17.
