塔里木盆地西南坳陷英吉沙与皮山地区构造演化特征及对油气成藏的影响

Tectonic evolution characteristics of Yingjisha and Pishan areas and the influence on petroleum accumulation in the southwest depression, Tarim Basin

塔西南坳陷油气勘探程度整体较低,复杂的构造演化制约了该坳陷油气成藏和勘探效果。与已发现的柯克亚等油气田具有相似油气地质背景的英吉沙与皮山地区,目前尚无大的发现。以平衡剖面技术为主线,并以野外踏勘所见地质现象和单井埋藏史作为约束条件,分析英吉沙与皮山地区的构造演化特征及其对油气成藏的影响。英吉沙地区自二叠纪以来经历4期构造推覆,发育叠瓦状、三角带和断弯背斜等构造样式,在中新世推覆作用最强,地层缩短率22.4%;皮山地区自二叠纪以来经历4期构造推覆,发育叠瓦状、断弯背斜等构造样式,上新世推覆最为强烈,地层缩短率12.5%;中新世以来英吉沙与皮山地区构造运动发生时间和作用强度存在一定差异。新近纪以来,英吉沙与皮山地区强烈逆冲推覆使得前渊坳陷带沉积了巨厚的新生代地层,导致下伏烃源岩进入高—过成熟阶段,开始大规模生烃,生成的油气可沿断层、不整合面向上运移到背斜构造等圈闭形成油气藏。新近纪以来英吉沙与皮山地区构造作用的差异性,导致其成藏条件具有一定差别:英吉沙地区的油气起始充注时间、构造圈闭主要形成时间均为中新世,上新世原生油气藏遭受破坏的风险较大;皮山地区的油气起始充注时间、圈闭主要形成时间均为上新世,油气藏后期的破坏风险较小。

The oil and gas exploration degree in the southwestern depression of the Tarim Basin is low overall.Complex tectonic evolution is one of the key factors that restrict the hydrocarbon accumulation and exploration in this depression.There are no major discoveries in the Yingjisha and Pishan areas that are geologically similar to those found in the oil and gas fields of Akmomu and Kekeya.Using a balanced section technology,and the geological circumstances and single well burial history as the constraints in the field,the tectonic evolution characteristics of the Yingjisha and Pishan areas and their effects on hydrocarbon accumulation were analyzed.Since the Permian,the Yingjisha area has undergone three stages of tectonic nappe,and developed tectonic styles such as imbricate thrusts,V-belt and fault related folds.It has the strongest nappe effect in the Miocene,with a strata shortening of 22.4%.The Pishan area has experienced four stages of tectonic thrust,developing styles such as imbricate thrusts and fault related folds.The strongest thrusting took place during the Pliocene with a strata shortening of 12.5%.There is a certain difference in time and intensity of tectonic movement in the Yingjisha and Pishan areas since the Miocene.Since the Neogene,the strong thrusting of the Yingjisha and Pishan areas has caused the formation of thick Cenozoic strata in the foreland depression,making the underlying source rocks enter the high-maturity and over-mature stage,resulting in large-scale hydrocarbon generation.Oil and gas migrated along faults and unconformities into anticline structures to form reservoirs.The difference in tectonic effects between the Yingjisha and Pishan areas since the Neogene has led to some differences in the conditions for hydrocarbon accumulation.The initial charging period of hydrocarbons and the main formation time of structural traps in the Yingjisha area were both in the Miocene epoch,and the primary oil and gas reservoirs were easily damaged in the Pliocene epoch.In the Pishan area,the initial charging period of hydrocarbons and the main formation time of structural traps were both in the Pliocene epoch,and the primary oil and gas reservoirs showed a low damage risk.