海拉尔盆地巴彦呼舒凹陷南屯组层序地层特征及有利区带预测

The Feature of Sequence Stratigraphy and Prediction of Favourable Exploration Belt of Bayanhushu Sag in Nantun Formation of Hailar Basin

巴彦呼舒凹陷的油气勘探不断有新的发现,展示其具有较大的勘探潜力,但目前勘探程度较低。通过对岩心、测井、录井、地震及古生物等资料综合分析,将南屯组(K_1n)划分为2个三级层序(SQ1、SQ2),在该基础上开展了沉积相类型及展布特征研究,进而预测有利区带。研究表明,K_1n沉积时期发育扇三角洲、辫状河三角洲和湖泊等3种沉积相类型。扇三角洲沉积相主要分布在研究区西部陡坡带;辫状河三角洲沉积相发育于东部的缓坡带;湖泊沉积相主要发育在中部洼槽带及扇(辫状河)三角洲的边部。沉积格局整体具有"东西分带"特征,从盆地陡坡带到盆地缓坡带,沉积相类型依次由扇三角洲逐渐过渡为滨浅湖、半深湖-深湖再演变为辫状河三角洲沉积。不同沉积演化时期,沉积体系分布有所差异,总体表现出水体由"深盆、深水"到"广盆、浅水"的变化,从SQ1到SQ2沉积时期,扇(辫状河)三角洲沉积规模明显变小。生、储、盖组合及成藏条件综合研究表明,扇三角洲前缘和辫状河三角洲前缘砂体储层物性较好,紧邻规模较大的优质烃源岩,在陡坡带断裂发育地区易形成陡坡反转构造油气藏;在缓坡带可形成断层-岩性油气藏;而靠近洼槽区易形成岩性油气藏。

New discoveries of oil and gas exploration have appeared continuously in Bayanhushu Sag,which showed great exploration potential,but the exploration level was low.Based on the integral analyses of core,well logging,mud logging,seismic and palaeontology data,Nantun Formation(K_1n)was divided into three third-order sequences SQ1 and SQ2),on the basis of study,the type and distribution of sedimentary facies were studied and the favourable belts were predicted.The results showed that Nantun Formation developed fan delta,braided river delta,lacustrine depositional systems,the fan delta was mainly distributed in the steep slope belt in the west,the braided river delta was developed in the gentle slope belt in the east,the lacustrine sediment was developed in the central sag and on the frontal edge of fan delta(braided river delta).Form the steep slope to the gentle slope belts,sedimentary facies was changed from fan delta to shore meare subfacies and half deep lake-deep subfacies and changed to the braided river delta,with the whole deposition pattern of"north and south blocks and east and west belts".The sedimentary distribution varied with deposition periods,the pattern was changed from "deep basin and deep water to the wide basin and shallow water".From SQ1 to SQ2,fan delta(braided river delta)became smaller significantly.The study of oil source,reservoir and cap assemblage and reservoir forming condition shows that the fan delta front subfacies,braided river delta front subfacies have good reservoir physical property and near to good source rocks,they are favorable exploration areas.The structural inversion reservoirs are likely to be formed in fracture developed steep slope belts,the fault and lithologic reservoirs are likely to be formed in the gentle slope zones;lithologic reservoirs likely to formed in the central area,the lithologic reservoirs are easily formed near the trough areas.