蒙古国塔南凹陷下白垩统铜钵庙组地震反射特征

Seismic reflection characteristics of Lower Cretaceous Tongbomiao Formation in Tanan Sag,Mongolia

铜钵庙组是塔南凹陷的重要含油气层位,精细研究其层序地层,有助于进一步对油气藏进行勘探和开发。主要利用地震反射特征,结合单井资料,对铜钵庙组进行了层序界面的识别,并首次在本区对层序内部体系域地震反射特征进行详细研究。铜钵庙组顶、底界面(T3、T5)为区域不整合面,分别表现为高角度不整合和"上超下剥"的反射特征;内部以T3--1为界分为2个三级层级(SQ1、SQ2)。T3--1为局部不整合面,主要表现为上超。体系域在本区东次凹上部层序SQ2中发育完整,被首次上超面、末次上超面和顶部的下超面分为LST、TST、HST和RST。在此基础上分析了铜钵庙组的内部反射结构,认为本区存在5种主要反射结构,其中,杂乱反射、楔状反射、前积反射地震相出现在山(陆架)前地区,代表扇三角洲沉积;亚平行反射、波状反射代表滨浅湖沉积或三角洲平原沉积;平行反射位于盆地地堑中心,代表半深湖、深湖沉积。

Tongbomiao Formation is an important horizon bearing oil and gas in Tanan Sag. Studying thor- oughly its sequence stratigraphy is beneficial for further exploration of the reservoir. Using the seismic reflection characteristics combined with single well data, the sequence interfaces are recognized, and the seismic reflection characteristics of the internal system traces are studied for the first time. The top and bottom interfaces of Tongbomi- ao Formation （ T3, T5 ） are regional unconformities and characterized by high angular unconformity with the ＂ up- side onlap and below denudation＂ reflection in feature. The Tongbomiao Formation can be divided into two se- quences in third order （SQ1, SQ2） by T3-1, which is a local unconformity with the onlop reflection. In the east-ern sub-sag, system tracts are fully developed in the upper sequence （SQ2）, and can be divided into LST, TST, HST and RST respectively by the first onlap interface, the last onlap interface and the downlap interface. Based on the fact, the internal reflection structures of Tongbomiao Formation have been analyzed. There mainly exist 5 kinds of reflection structures, named disorder-, foreset-, wedge-shaped-, parallel and sub-parallel or wavy-shaped reflec- tions. Among them, the first three reflections mainly appear on the front of mountains, representing the fan delta sediments, the sub-parallel or wavy-shaped reflection representing the shallow lake or fan delta plain sediments, and the parallel reflection represents the semi-deep lake or deep lake sediments.