夏河地区构造演化及成藏耦合关系研究

TECTONIC EVOLUTION AND ITS COUPLING WITH RESERVOIRING IN XIAHE AREA OF BACHU UPLIFT, THE TARIM BASIN

夏河地区位于塔里木盆地巴楚隆起中段的北部,20世纪90年代以来,巴楚隆起南缘相继发现了一批以构造圈闭为主体的油气藏。因此,在巴楚隆起区域构造演化背景上分析夏河地区的油气成藏规律,对指导该区油气勘探具有重要意义。通过研究该区构造圈闭的演化特征,并结合生储盖等成藏条件分析,初步理清了成藏条件的时空耦合关系。研究发现:该区构造的发育主要受断裂活动的控制,现今的构造圈闭都经过多期构造运动的改造。海西晚期—中生代早期为夏河地区成藏第一关键期,中下寒武统烃源岩处于生烃高峰期,卡北构造和卡拉沙依构造先后达到最佳圈闭形态,成藏条件达到最佳匹配关系;随后,中下寒武统烃源岩停止生烃,圈闭的演化决定着古油气藏的保存程度;喜山中期为夏河地区成藏第二关键期,该期构造活动强烈,卡拉沙依构造由断背斜向断鼻形态发育而使古油气藏遭受严重破坏,卡北构造的圈闭幅度有所减小,但仍具备形成中下寒武统残存气藏的条件;随后,该区构造形态基本定型,卡北残存构造能否继续捕获阿瓦提凹陷油气决定着该构造的现今油气规模及勘探前景。

Xiahe area is located in the northern part of the central Bachu uplift in the Tarim Basin. Many oil and gas pools dominated by structural traps have been successively discovered on the south margin of Bachu uplift. Therefore, an analysis of the hydrocarbon reservoiring patterns of Xiahe area in the background of regional tectonic evolution of Bachu uplift is of great significance for guiding petroleum exploration in the study area. The temporal and spatial coupling of reservoiring conditions is preliminarily recognized through studying the evolutionary characteristics of the structural traps in the study area and in conjunction with an analysis of the reservoiring conditions, such as source rocks, reservoirs and seals. The tectonic development in the study area is mainly controlled by faulting and the present structural traps have experienced reformation resulted from multiphase tectonic activities. Xiahe area went into the first critical reservoiring stage during Late Hercynian and Early Mesozoic. The Lower-Middle Cambrian source rocks went into peak hydrocarbon generation, and the optimum trap shapes appeared in Kabei and Karasay structures successively, leading to an optimum combination of reservoiring conditions. Afterwards, the Lower-Middle Cambrian source rocks stopped generating hydrocarbon and the trap evolution determined the preservation of pa-leo-pools. The Middle Himalayan was the second critical reservoiring stage of Xiahe area, during which tectonic activities were strong. Karasay structure evolved from a faulted anticline to a fault nose, resulting in serious destruction of the paleo-pools. The closure of Kabei structure decreased to some extent, but the conditions still existed for the formation of relic Lower-Middle Cambrian gas reservoirs. Afterwards, the structures in the study area basically finalized, whether the relic Kabei structure could go on trapping hydrocarbons generated from Awati sag determined the present scale of oil and gas pools and their exploration potential.