鄂尔多斯盆地北部杭锦旗马家沟组四段碳酸盐岩储层分布规律

Distribution of paleo-karst reservoirs in Ma 4 Member, Hangjinqi area, northern Ordos Basin

张威 丁晓琪 李春堂 祁壮壮

Wei Zhang Xiaoqi Ding Chuntang Li Zhuangzhuang Qi

鄂尔多斯盆地北部灰岩喀斯特储层是近年发现的一种新储层类型，分析其形成机理与分布规律对该地区的天然气勘探意义重大。通过洞穴结构解剖，分析储层与洞穴相的关系；在洞穴测井响应研究的基础上，拉平基准面，研究风化壳古地貌和洞穴层的纵向分布规律，阐释多层洞穴与构造隆升之间的关系；利用地震资料，进行洞穴的分布规律研究。结果表明：①不整合面之下的表层孔洞大多被泥质充填而失去储集能力，远离不整合面的洞穴是喀斯特储层的主要储集空间；②洞顶相和洞穴未充填相是主要的储层发育段；③马四段灰岩发育三层洞穴，洞穴层分布稳定，平面上可对比性强，西部发育程度好于东部，三层洞穴是加里东期盆地北部幕式隆起的结果；④井-震结合对洞穴分布进行预测，北部以大量的落水洞为特征，向南转变为地下暗河；洞穴在平面上呈网状分布，断裂对其影响不大。古潜水面控制着洞穴的分层。马四段多层灰岩洞穴的发育极大地拓展了盆地北部下古生界的天然气勘探范围。

Karst limestone reservoir, a newly recognized reservoir type with hydrocarbon potential in recent years, is also present in the northern Ordos Basin.Its forming mechanism and distribution pattern are of great significance for future gas exploration in the area.Studies were carried out on samples from the area on the relationship between cavern facies and the reservoir through cavern anatomy, on the paleotopography of weathering crust and vertical pattern of the multiple cave layers through cavity logging and levelling interpretation to explain the relationship between multi-layers of caverns and structural uplift, and on the distribution pattern of caverns based on seismic data.The results show that vugs occurring below the unconformity are mostly filled with clay and fine-grained debris, thus incapable of storing.However, those far away from the unconformity are dominant reservoirs.Cave roof and unfilled cavities are also dominant reservoir space.Three layers of caverns, a result of periodic uplifting in northern part of the study area during the Caledonian, are developed in Ma 4 Member in a steady distribution and good well-to-well correlation.The cavities are more developed in the west of study area compared with the east part.The prediction of cavity distribution by well-seismic correlation indicates that sink holes mostly occur in the north, and underground channels mostly occur in the south.Cavities show a network-shaped distribution in plane view, implying a minor controlling effect by faults.Paleo-water table serves to control the stratification of cavities.The discovery of three layers of cavities in Ma 4 Member broadens the horizon of gas exploration in the northern Ordos Basin.

10.11743/ogg20210308