榆林气田长北区块山西组下段主力储集层建模及水平井地质设计

Main reservoir modeling and horizontal drilling design for the lower Shanxi Formation in the Changbei Block of the Yulin Gas Field, Ordos Basin

鄂尔多斯盆地东部榆林气田长北区块主力储集层是下二叠统山西组下段的石英砂岩 ,将用水平井开发。为编制水平井开发方案而进行的气藏地质研究结果表明 :石英砂岩是连续分布的席状砂体 ,发育于横向迁移极大的辫状河沉积环境中的内切河谷 ,轴部多层河道辫状冲积的叠加厚度平均约 15 .77m ,主河道两侧渐变为单层河道 ,估计多层河道砂体宽 5～ 3 0km、厚 9～ 40m ,单层河道砂体宽 0 .2 5～ 1km、厚 5～ 8m。石英砂岩粗—很粗粒结构和成分成熟度高都有利于保存储集层原生孔隙空间 ,但其内部存在阻流带 ,估计垂向阻流带的平均间距为 60 0m ,利用水平井可以降低阻流带的影响。根据气藏地质研究成果 ,考虑长北区块河道方向和地层最小水平应力 (压应力 )方向 ,进行 2口水平井地质设计 ,钻井过程中通过随钻测井随时调整钻井轨迹。图 4表 1参

The main reservoir in the lower Shanxi Formation (Lower Permian) is composed of quartz sandstones in Changbei Block of the Yulin Gas Field in the east Ordos Basin. This reservoir will be developed through horizontal drilling. Reservoir modeling reveals that the quartz sandstones are continuously distributed sheet sands, formed in inner incised valleys of laterally migrating braided channels. The average accumulated thickness of the sheet like sandstones at the axial part is 15.77 m. It gradually changes into single layer on both sides of the main channel. The dimensions of the multi layer sandstones are 5 30 km wide and 9 40m thick. A single layer sandstone is 0.25 1 km wide and 5 8m thick. The coarse to very coarse nature and high component maturity of the quartz sandstones are favorable for keeping original porosity. However, there are internal fluid barriers due to heterogeneity of the sediments. The average spacing of such barriers is 600m. The two horizonal wells are designed to drill through these barriers and to connect the reservoirs. The horizontal drilling will be steered based on LWD data.