鄂尔多斯盆地吴起地区延长组长4+5段储层非均质性特征

Heterogeneity of Reservoirs in the Member Chang 4 + 5 of Triassic Yanchang Formation in the Wuqi Area of Ordos Basin

储层非均质性对剩余油分布和水驱或气驱波及系数影响较大,开展储层非均质精细评价,是油田开发方案调整和剩余油挖潜必不可少的内容。利用密井网测井资料和岩矿鉴定等资料,从沉积、成岩作用等方面对吴起油沟油田长4+5段储层非均质进行了研究。结果表明,研究区长4+5段诸层为三角洲前缘沉积末端,单期水下分流河道规模较小且改道频繁,层内泥质夹层不发育,层间隔层发育,单砂体连通性差,非均质性较强;纵向上将长4+5段分为长4+51、长4+521、长4+522三个小层,受沉积环境和成岩作用,特别是碳酸盐胶结作用的影响,层内非均质性多为正韵律或复合韵律,其中长4+51储层非均质性最强,长4+522储层非均质性最弱;从层间非均质性来看,其中长4+51单层砂体薄,分层系数最大,长4+522储单层砂体厚度大,分层系数较小;从平面非均质性来看,长4+51砂体呈交切窄条带状发育,砂体厚度横向变化大,平面非均质性较强;长4+521砂体呈孤立条带状分布,砂体欠发育,以分流涧湾为主;长4+522砂体厚度大,且呈连片发育,平面非均质性较弱。

Reservoir heterogeneity has a great impact on remaining oil distribution and water-flooding or gas-driving sweep efficiency.So evaluating reservoir heterogeneity exquisitely is essential in adjustment of the oilfield development plan and residual oil tapping.Using data of logging of a dense well network and rock-ore identification,focusing on sedimentation and diagenesis,this work studies the heterogeneity of reservoirs in member Chang 4+5 of the Yougou oil field in the Wuqi area,Ordos Basin.Results show that this section is the end of a delta front,where the single stage underwater distributary channel is small that diversiformed frequently,with a little argillaceous sandwich and many inter-layers,poor single sand-body connectivity and strong heterogeneity.In vertical direction,it is divided into three sub-layers of Chang 4+51,Chang 4+521,and Chang 4+522.Influenced by the deposition environment and diagenesis,especially the carbonate cementation,the heterogeneity is mostly positive or composite rhythm,and Chang 4+51 has the strongest heterogeneity while Chang 4+522 has the weakest heterogeneity.In terms of the inter-layer heterogeneity,Chang 4+51 has thin single layer sand bodies and the largest layering coefficient,Chang 4+522 has thick single layer sand bodies and smaller layering coefficient.From the perspective of planar heterogeneity,Chang 4+51 hosts many intersecting narrow strips and highly variable thicknesses of sand bodies,showing intense planar heterogeneity.Sand bodies in the sub-layer Chang 4+521 are distributed as isolated strips,of underdevelopment,dominated by distributary channels.Sand bodies in Chang 4+522 are relatively thicker,more continuous,exhibiting weak planar heterogeneity.