基于测井资料的古地貌-不整合识别及控藏特征研究——以鄂尔多斯盆地三边地区中生界为例

Identification and reservoir-controlling characteristics of paleogeomorphology-unconformity based on well logging data:a case study of Mesozoic in the Sanbian area of Ordos Basin

鄂尔多斯盆地三边地区三叠系顶不整合对下部延长组和上部延安组的油气成藏有着重要的影响,为了查明该不整合的发育规模、与古地貌的关系及对成藏的贡献,利用测井方法进行了古地貌恢复和不整合结构定量划分,并分析了不同古地貌单元不整合结构及其控藏特征.结果表明:(1)三叠系古地貌分为河谷、河间丘、坡嘴、斜坡带和高地共5个单元,风化黏土层主要在坡嘴和斜坡发育,风化淋滤带主要在河谷和高地发育,其次是斜坡和坡嘴;(2)建立了不整合结构测井定量划分的标准,风化黏土层:PC_(1)≥250,PC_(2)≤90,风化淋滤带:PC_(1)≤250,PC_(2)≤90或PC_(1)≥250,PC_(2)≥90;未风化原岩:PC_(1)≤250,PC_(2)≥90;(3)三叠系顶不整合作为“中转站”,与上部延9-延10段、下部长21-长23未风化岩石层之间形成具有“竞争”关系的3个含油气层,油气分布呈“互补”特征.

The top unconformity of the Triassic in the Sanbian area of the Ordos Basin has an important influence on the hydrocarbon accumulation of the lower Yanchang Formation and the upper Yan'an Formation.In order to find out the development scale of the unconformity,its relationship with paleogeomorphology and its contribution to the hydrocarbon accumulation,the paleogeomorphic restoration and unconformity structure are quantitatively divided by logging method,and the unconformity structure and reservoir-controlling characteristics of different paleogeomorphic units are analyzed.The results show that:(1)The paleogeomorphology of the Triassic is divided into five units:valley,inter-river hill,slope mouths,slope and highland.The weathered clay layer mainly develops in the slope mouths and slope,and the weathered leach zone mainly develops in the valley and highland,followed by slope and slope mouths;(2)The quantitative classification criteria of unconformity logging are established.The weathering clay layer is PC_(1)≥250,PC_(2)≤90,and the weathering leaching zone is PC_(1)≤250,PC_(2)≤90 or PC_(1)≥250,PC_(2)≥90.Unweathered protolith:PC_(1)≤250,PC_(2)≥90;(3)As a“transfer station”,the top unconformity of the Triassic system forms three OB(oil and gas-braring bed)with a“competitive”relationship with the upper Yan 9-Yan 10 member and the lower Chang 21-Chang 23 unweathered rock layer,and the oil and gas distribution is“complementary”.