非洲Muglad盆地Fula凹陷白垩系AG组岩性油气藏勘探潜力

Exploration potential of lithologic reservoirs of Cretaceous AG Formation in Fula Sag,Muglad Basin,Africa

借鉴国内断陷盆地岩性油气藏勘探理论与技术,运用层序地层学分析方法,对中非裂谷系Muglad盆地Fula凹陷开展多级次层序地层划分、烃源岩地化分析、油气成藏规律研究和有利区带划分与潜力评价。研究结果表明:①受基准面旋回发育控制,Fula凹陷AG组可划分为5个三级层序,湖泛面附近是岩性油气藏最有利分布位置。②研究区AG组主要发育三大物源体系,福西陡坡带为短轴近物源快速沉积,相带平面展布较窄;东北部发育辫状河三角洲沉积,展布范围较大,沉积持续时间长;AG组沉积晚期在东南部发育一套展布范围较小的辫状河三角洲沉积;三角洲前缘和滨浅湖滩坝是岩性油气藏发育的有利相带。③AG组AG2段(SQ4)暗色泥岩主要沉积于浅湖—半深湖环境,干酪根类型为Ⅰ—Ⅱ1型,TOC平均为3.41%,生烃潜量(S1+S2)多大于8 mg/g,为好—极好烃源岩,可为构造-岩性油气藏的形成提供充足的油气来源。④AG组可划分出7个岩性油气区带,其中Fula-Moga斜坡带北部成藏条件优越,勘探潜力大。

Referring to the domestic exploration theory and technology of lithologic oil and gas reservoirs in fault basins,sequence stratigraphy analysis method was used to carry out multi-scale sequence stratigraphy division,geochemical analysis of source rocks,research on hydrocarbon accumulation rules,favorable zone division and potential evaluation of Fula Sag in Muglad Basin of Central African Rift System.The results show that:(1)Five third-order sequences can be identified based on the sea level changes,and the flooding surface is the most favorable vertical location for lithologic reservoirs.(2)There are three major provenance systems in AG Formation in the study area.Fula-west steep slope belt is short-axis with rapid deposition and narrow distribution of facies zones.Braided river delta system is continuously developed with wide distribution in the northeastern part of the study area,and braided river delta system is limited developed in the southeastern part at the later period.The delta front and beach bar in shore-shallow lacustrine are the most favorable sedimentary facies for lithologic reservoirs.(3)Grey-dark mudstones developed in AG2 member(SQ4 sequence)of AG Formation are mainly deposited in shallow lake to semi-deep lake environment.The kerogen is typeⅠ-Ⅱ1,the average total organic carbon(TOC)content is 3.41%,and the hydrocarbon generation potential(S1+S2)is greater than 8 mg/g,which are good-excellent source rocks and the material basis for the forming of structural-lithologic reservoirs.(4)The AG Formation can be divided into seven lithologic reservoirs zones,among which the northern Fula-Moga slope zone has favorable conditions for hydrocarbon accumulation and great exploration potential.