North Carnarvon盆地Exmouth低隆起成藏条件及勘探潜力研究

近年来,随着勘探技术的革新,North Carnarvon盆地Exmouth低隆起深水区的油气勘探获得了巨大突破。Exmouth低隆起主要发育一套遍及全盆地的优质烃源岩,即中上三叠统Mungaroo组浅水辫状河三角洲相的暗色泥岩夹薄煤层,其有机质丰度较高(平均质量分数为4.61%),有机质类型为Ⅱ2—Ⅲ型,以生气为主,成熟度适中(0.46%<Ro<1.89%),有较强的供烃能力。晚三叠世开始的构造隆升作用使得上覆侏罗系与下白垩统厚度均较薄,机械压实作用较弱,使中上三叠统水道砂体储集性能较好;晚侏罗世—早白垩世期间,Exmouth低隆起同样发育牛津组大型滩坝砂体与Barrow三角洲优质储层。Exmouth低隆起发育了自生自储式和下生上储式2套成藏组合,其中自生自储式成藏组合以Mungaroo组水道砂体为储集层,以Mungaroo组暗色泥岩为烃源岩和局部盖层,勘探潜力最好。综合考虑Exmouth低隆起的烃源岩条件、储集条件及成藏组合条件,避开油气渗漏带展布范围,预测油气勘探有利区带位于其东部及西南部。

板块运动对Exmouth高地演化和油气勘探的影响

North Carnarvon盆地位于澳大利亚西北大陆架的南部,是一个自晚古生代至新生代持续沉降形成的巨型含油气盆地,其中Exmouth高地是该盆地主要的地质单元,自2008年以来发现三叠系Mungaroo组气田30个。在对Exmouth高地进行地震资料解释时发现,该区域具有许多特殊的地质现象,如具有大量各异的区域不整合面;断裂系统靠近外缘展布且具有一定规律;三叠系三角洲地层沉积现象特殊等。结合区域地质资料,利用板块运动理论,进一步对上述现象进行了分析和总结。通过对各个时期区域板块间相对位置和相对运动的分析发现,板块运动控制着这个区域的构造沉积演化,进一步控制着区域的油气成藏。通过对板块运动的研究,总结了区域油气勘探的一般性规律。

Petroleum geology and exploration direction of gas province in deepwater area of North Carnarvon Basin, Australia

North Carnarvon Basin is a gas province with minor oily sweet spots in deepwater area with water depth more than 500 m,which is one of the hot spots of global petroleum exploration for its series of giant hydrocarbon discoveries in recent years.However,the degree of oil and gas exploration in deepwater area is still low,and the conditions for oil and gas accumulation are not clear.Based on the current exploration situation and latest database of fields,applying multidisciplinary analysis of hydrocarbon geology,hydrocarbon accumulation elements and its exploration direction of North Carnarvon Basin in deepwater area are analyzed.The results show that there are three sets of main source rocks in deepwater area of North Carnarvon Basin,which are Triassic marine shale in Locker Formation and delta coal-bearing mudstone with thin carbonaceous mudstone in Mungaroo Formation,Lower–Middle Jurassic paralic carbargilite and coal measure strata in Athol Formation and Murat Formation,Cretaceous delta mudstone in Barrow Group and marine shale in Muderong Formation.Most source rock samples show gas-prone capability.The coarse sandstone of delta facies in Middle–Upper Triassic Mungaroo Formation is the most important reservoir in deepwater area,Lower Cretaceous Barrow Group deep-water gravity flow or underwater fan turbidite sandstone is the secondly main reservoir.Lower Cretaceous marine shale in Muderong Formation is most important regional caprock.Triassic mudstone in Mungaroo Formation is an important interlayer caprock in deepwater area.There are two main reservoir accumulation assemblages in deepwater area,one is Triassic structural-unconformity plane reservoir accumulation assemblage of Locker Formation to Mungaroo Formation,and the other is Lower–Middle Jurassic Athol Formation and Murat Formation–Lower Cretaceous stratigraphic lithology-structural reservoir accumulation assemblage of Barrow Group to Muderong Formation.There are three main control factors of hydrocarbon Accumulation:One is coupling of source and seal control hydrocarbon distribution area,the second is multi-stage large wave dominated deltas dominate accumulation zone,the third is direction of hydrocarbon migration and accumulation in hydrocarbon-rich generation depression was controlled by overpressure.The south of Exmouth platform in deepwater area is adjacent to hydrocarbon rich depression zone,reservoir assemblage is characterized by“near source rocks,excellent reservoir facies,high position and excellent caprocks”,which is the main battlefield of deepwater oil and gas exploration in North Carnarvon Basin at present.There are a lot of fault block traps in the northern structural belt of Exmouth platform,and the favorable sedimentary facies belt at the far end of delta plain in Mungaroo Formation is widely distributed,which is the next favorable exploration zone.The Lower Cretaceous,which is located at the concave edge uplift adjacent to the investigator depression and the Exmouth platform,also has a certain exploration prospect in northwest of deepwater area.