北羌塘坳陷上三叠统沉积模式及对油气勘探的启示

Sedimentary model and its implications for oil and gas exploration of Upper Triassic in Northern Qiangtang Depression

关键词:  羌塘盆地  上三叠统  层序  沉积模式  成藏模式

Key words:  Qiangtang basin  Upper Triassic series  sequence  depositional model  hydrocarbon accumulation model

摘要:

基于北羌塘坳陷上三叠统基干剖面实测资料，开展地层层序划分对比和沉积相研究，建立沉积演化模式，揭示对羌塘盆地油气勘探的指示意义。结果表明：（1）北羌塘坳陷晚三叠世卡尼期—诺尼期可以划分为2个Ⅲ级层序，区域上沉积了4套地层，第1个Ⅲ级层序对应于甲丕拉组（LST）和波里拉组（TST、HST），第2个Ⅲ级层序对应于阿堵拉组（SMT、TST和HST）和夺盖拉组（RST）；（2）北羌塘坳陷甲丕拉组沉积期主要沉积相为扇三角洲和三角洲，波里拉组沉积期可分为沿岸生物礁模式、远端变陡缓坡模式和碳酸盐岩台地模式，阿堵拉组沉积期主要以海岸、浅海陆棚相和三角洲相为主；（3）波里拉组外缓坡亚相和阿堵拉组浅海陆棚相可形成良好的灰泥岩类烃源岩，其中以阿堵拉组广覆式浅海陆棚相泥质烃源岩最重要，波里拉组油苗以海相成因和中高成熟度为主，主要来源于波里拉组外缓坡亚相泥灰岩，后期低熟油来自阿堵拉组浅海陆棚相混合型有机质。北羌塘坳陷发育多个大型富烃凹陷，上三叠统具有良好的生烃成藏条件，研究对深化羌塘油气地质认识，聚焦油气勘探目的层系具有重要地质意义。

Abstract:

Based on the measured data of the Upper Triassic section in the Northern Qiangtang Depression, We have studied the stratigraphic sequence and sedimentary facies, established the sedimentary evolution model, and revealed the indicative significance for oil and gas exploration in the Qiangtang Basin.The results show that:(1) the Late Triassic Carnian-Norian in the North Qiangtang Depression can be divided into two third-order sequences, with four sets of strata deposited in the area. The first third-order sequence corresponds to the Jiapila Formation(LST) and the Bolila Formation(TST and HST), the second third-order sequence corresponds to The Adula Formation(SMT,TST and HST) and the Duogaila Formation(RST). (2) The main sedimentary facies of the Jiapila Stage in the North Qiangtang Depression are fan delta and delta; the depression during Bolila period shows the coastal reef model, the distal steepening and gentle slope model and carbonate platform model, respectively; the Adula Formation and Duogaila Formation are dominated by shallow sea shallow shelf facies and delta facies, respectively; (3) the outer gentle slope facies of the Bolila Formation and the shelf facies of the Adula Formation are conducive to the formation of good source rocks, among which the widely developed shelf muddy source rocks of the Adula Formation are the most important. The oil in the Bolila Formation is mainly of marine origin and medium to high maturity, and mainly comes from the outer gentle slope facies marl of the Bolila Formation. The late low-maturity oil comes from the shelf-transitional facies Mixed organic matter of the Adula Formation.The North Qiangtang Depression has developed several large hydrocarbon-rich sags, and the Upper Triassic horizon has favorable conditions for hydrocarbon generation and accumulation. The study is of great geological significance to deepen the geological understanding of oil and gas in the Qiangtang and focus on the target formations for oil and gas exploration.