塔里木盆地库车坳陷盐构造变形平衡恢复及相关问题讨论

Discussion on balance restoration of salt structure deformation and related problems in Kuqa Depression,Tarim Basin

塔里木盆地库车坳陷发育古近系和新近系2套膏盐岩,盐下中生界已经落实万亿方天然气储量,是我国重要的天然气产区。库车坳陷盐下中生界构造型油气藏是油气勘探的重点,盐构造样式解析、盐构造变形机制、盐构造平衡恢复及变形期次分析是库车坳陷盐构造研究的难点。利用高精度三维地震拼接剖面、钻井和区域地质资料,选取库车坳陷西段和东段2条典型剖面,通过3DMove软件进行盐构造平衡恢复,分别恢复盐上层、盐下层和盐层的构造变形,复原构造变形前地震剖面。并针对复原过程中的具体问题,从盐构造恢复方法、变形特征、演化、变形机制等4个方面进行讨论。研究结果表明盐层的恢复需要满足2个基本假设:一是忽略由于挤压造成的岩石内部缩短量;二是近似认为弱变形区或未变形区盐层的厚度不变。库车坳陷发育2期盐构造:渐新世—中新世(构造稳定期)盐层上覆地层重力差异作用诱发早期盐构造,发育盐底辟、盐丘等盐构造;上新世—全新世(构造活动期)破坏和改造早期盐构造,发育挤压型盐构造。挤压作用、盐层塑性流动是盐构造形成的主要原因:盐上层发育盐滑脱逆冲断层,盐层塑性变形形成盐背斜、盐席、盐墙;盐下层发育叠瓦状逆冲断层,靠近造山带附近发育大型构造楔。沉积差异负载是诱发早期盐构造形成的主要因素,盐丘、盐底辟等早期盐构造主要发育于冲积扇前端。中生界滑脱层和基地古隆起控制盐下冲断构造的边界。膏盐层的厚度、分布范围控制着盐下逆冲推覆构造发育的数量和规模,库车坳陷西部仍然是油气勘探的重点。中生界向古隆起超覆沉积带,有利于地层岩性油气藏的发育和保存,是重要的油气勘探领域。

Kuqa Depression has developed two sets of Palaeogene and Neogene paste salt rocks,with trillion cubic meters of natural gas reserves in pre-salt Mesozoic,which is an important natural gas production area in China.The structural oil and gas reservoir of Lower Mesozoic in Kuqa Depression is the focus of oil and gas exploration.The analysis of salt structure style,salt structure deformation mechanism,salt structure balance recovery and deformation period analysis are the difficulties of salt structure research in Kuqa Depression.In this paper,using high-precision three-dimensional seismic splicing profile,drilling and regional geological data,two typical sections of the western and eastern sections of the Kuqa Depression are selected.The structural balance recovery is carried out by 3DMove software,and the structural deformation of the upper salt layer,the lower salt layer and the salt layer are restored respectively.The seismic profile before structural deformation is restored.In view of the specific problems in the recovery process,the salt structure recovery method,salt structure deformation characteristics,salt structure evolution,and salt structure deformation mechanism are discussed.The results show that the recovery of the salt layer needs to meet two basic assumptions:One is to ignore the amount of internal rock shortening caused by extrusion;the other is that the thickness of salt layer in the weakly deformed or undeformed area is approximately constant.Kuqa Depression developed two salt structures:Oligocene-Miocene(tectonic stable period)on the salt layer formation gravity difference induced early salt structure,developed salt dioper,salt mound structure.Oligocene to Miocene(tectonic stable period)overlying strata gravity difference induced the early salt structure,salt diapir,salt dome and other structures,Pliocene to Holocene(tectonic active period)destroyed and reformed the early salt structure,the development of extrusion salt structure.Extrusion action and plastic flow of salt layer are the main reasons for the formation of salt structure.The salt slip and unthrust fault develops in the upper salt layer,and the plastic deformation of the salt layer forms the salt anticline,salt mat and salt wall to develop in the lower salt layer,and the large structural wedge develops near the orogenic belt.Deposition differential load is the main factor inducing the formation of the early salt structure.The early salt structure such as salt mound and salt diopia mainly develops at the front end of the alluvial fan.The boundary of Mesozoic and base ancient uplift.The thickness and distribution range of the paste salt layer control the quantity and scale of the thrust cover structure development under the salt,and the west of Kuqa Depression is still the focus of oil and gas exploration.The overlying sedimentary zone from the Mesozoic boundary is conducive to the development and preservation of the formation of lithological oil and gas deposits,and it is an important field of oil and gas exploration.