有限充注动力背景下致密储层油水差异成藏再认识——以鄂尔多斯盆地华池地区延长组8段为例

鄂尔多斯盆地西南部延长组8段致密储层已发现如西峰和姬塬等油藏连片富集区，但在进一步勘探部署时亦发现如华池和城壕等油水差异富集区，储层中油藏的主控因素和分布规律不明。通过对华池东西部烃源岩条件、源储接触关系、砂体规模、储层物性及非均质性的对比解剖，探讨了油水差异富集区原油的成藏主控因素和富集规律。研究结果表明，源储压差作为致密油的主要成藏动力，其在倒灌运移模式下所能提供的原油充注动力有限。造成华池东西部油水差异富集的主控因素有源储间发育的泥质隔层、砂体发育规模和储层非均质性。其中泥质隔层决定了原油能否向下运移，砂体规模决定了原油能否侧向封堵，储层非均质性决定了单砂体中原油的差异性富集。在有限的充注动力背景下，规模大、整体物性好、均质性强的储层不利于致密油的富集，反而规模小、整体物性较差、非均质性较强的储层因容易形成岩性和物性遮挡而更利于致密油的富集。结果不同以往“好砂带找油”的观点，对鄂尔多斯盆地油水差异富集区下一步的勘探具有一定的参考价值。

Further understanding of differential accumulations of oil and water in tight sandstones with limited charging power:A case study of Chang 8 member in Huachi area,Ordos Basin,China

Batches of tight oil reservoirs including Jiyuan and Xifeng reservoirs were found in the 8th member of Yanchang Formation (Chang 8 member) in southwest Ordos Basin.Further exploration in the place reveals some areas with differential accumulations of oil and water such as Huachi and Chenghao areas.Nevertheless, the main controlling factors and distribution patterns of these accumulations are unknown.Based on a detailed discussion on source rock quality, source-reservoir contact relationship, sand body scale, physical properties and heterogeneity of reservoir in eastern and western Huachi area, this study explores the controlling factors and accumulation patterns of oil reservoirs in the differential areas.The results show that the pressure difference between source and reservoir is the main driving force of tight oil accumulations, but provides only limited charging power with backward migration.The factors controlling the differential accumulation of oil and water in eastern and western Huachi area are the argillaceous barriers grown between source and reservoir, sand body size and reservoir heterogeneity, of which, the argillaceous barriers control the downward migration of crude oil, the size of sand body serves as the lateral sealing for crude oil, and the reservoir heterogeneity determines the differential accumulation of crude oil in a single sand body.Given the limited charging power, reservoirs that are large in scale, good in physical properties and strong in homogeneity, are not ideal harbors for oil to accumulate.On the contrary, reservoirs that are small in scale, poor in physical properties and strong in heterogeneity, are more readily to provide lithological or physical barriers to stop the escape of oil.This understanding, quite different from the previous viewpoint that "high-quality sands indicate good oil traps", may serve to shed light on the further exploration in the differential areas of the Ordos Basin.