A STUDY ON THE DISTRIBUTION PATTERN OF SUPRASALT FAULT BASED ON NUMERICAL SIMULATION
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摘要: 盐上断层的形态和分布模式主要由其下部盐体形态和盐拱起所产生的上拱力共同控制。对盐上断层形成机制和分布模式的定量研究在盐上断层解释与预测、盐体形态描述及油气运移和成藏等方面具有重要意义。在总结上拱力与其上断层形态定量关系的基础上,针对盐构造中三种典型的盐体形态类型,分别拟合上拱力分布模式,并数值模拟其所产生的盐上断层形态和分布模式。模拟结果表明:(1)在产生恒定上拱力的盐构造中,发育两组相对称、深度分布一致的断层,每组断层相平行;(2)在产生线性变化上拱力的盐构造中,发育主次两组倾向相反的断层,主断层分布较浅,次断层分布较深,多被主断层限制,每组断层内,断层分布随上拱力变小而线性变深,而其形态不发生变化;(3)在产生抛物线形上拱力的盐构造中,两组主断层倾向相反相互对称,每组断层内,从构造中心到边部,断层倾角变缓,分布变深,构造边部出现次级小断层多被主断层限制。模拟结果与自然界盐体形态和断层分布模式吻合性较好,证实了模拟基于的上拱力与断层形态定量关系理论和模拟结果的正确性。Abstract: The shape and distribution patterns of upsalt faults are mainly controlled by the shape of the lower part of the salt body and its corresponding upwelling force. The quantitative research on the formation mechanism and distribution pattern of upsalt faults plays an important role in the interpretation and prediction of upsalt faults, description of the shape of the salt body as well as the migration and accumulation of oil and gas. According to the quantitative relationship between the upwelling force and the shapes of the upsalt faults, three typical types of salt structures are identified in this paper.The distribution pattern of upwelling force is estimated and numerical modeling is conducted respectively for the three types of salt bodies, based on the quantitative relationship. Accordingly, the modeling results show that (1) In the salt structure with constant upwelling force, two symmetrical fault groups with consistent depth distribution are formed parallelly. (2) In the salt structure with linearly changing upwelling force, two fault groups with reversed directions are formed, in which, the distribution of the main faults is shallow and that of the secondary faults is deep and often limited by the former. Within each fault, the fault distribution linearly deepens as the upwelling force weakens, while the shape is not changed. (3) In the salt structure with parabola upwelling force, the two main fault groups are symmetrical with reverse directions. Within each fault, from the tectonic center to the edge, the inclination of the fault becomes less steeper while the distribution deeper, and there are emergence of the secondary faults mostly controlled by the main faults.The simulation results accord with the shape and the fault distribution pattern of the natural salt bodies, which confirms the theory of quantitative relation between upwelling force and shape of fault and the correctness of the simulation results.
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图 7 Reitbrook盐底劈构造盐上断层模式[22]
a—Reitbrook盐拱构造古近系底部构造图; b—Reitbrook盐拱构造的剖面图。红色框内为被主断层限制的反向小断层
Figure 7. The pattern of upsalt fault of Reitbrook dome
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