源储间泥/钙质等隔层对陆相致密油（低渗透油藏）成藏控制机理研究

“Sweet spot” always plays an important role in exploration of terrestrial tight oil (reservoirs with low permeability) now which accumulates continuously in or near the source rocks, but sometimes these areas next to high-quality source rocks confuse us for no oils or much water. Therefore, how to make optimization on “sweet spot” needs to be reinterpreted. Mud/calcium interlayers developing between source rocks and reservoirs which result from frequent alternations of sedimentation and diagenesis have a great effect on the migration and accumulation of tight oil (reservoirs with low permeability). In this study, typical terrestrial tight oil in Yanchang formation, Erdos Basin is taken as an example. Through core observation, different logging characters, the high resolution sequence stratigraphy, mud/calcium interlayers, tight sandstone with argillaceous laminated and sand-mud-transition sections of tight gas in different areas are defined and relevant geological models are also established. Furthermore, detailed researches on the hydrocarbon-generating pressurization of Chang7 source rocks and breaking through different interlayers are made by physical simulation experiments and numerical simulations to make out the relationships between hydrocarbon generation charging dynamic power and interlayer resistance as well as the controlling factors on tight oil under different types of interlayers between source rocks and reservoirs, perfecting the theoretical basis of terrestrial tight oil in our country.

“甜点”区的准确预测是陆相致密油（低渗透油藏）勘探的关键，目前认为致密油的特征是源储一体或近源成藏，并呈大面积分布，但我国一些致密油区中却出现了邻近优质源岩分布的“甜点”区不含油甚至出大水的现象。因此“甜点”区需重新认识。陆相地层沉积与成岩作用变化频繁，易在源储之间形成泥/钙质等隔层，这对致密油（低渗透油藏）的运移及成藏有着重要影响。本项目拟以鄂尔多斯盆地延长组典型陆相致密油为研究对象，通过大量岩心观察和高分辨率层序地层学研究，结合不同类型岩性测井响应特征，明确不同区块致密油源储间泥/钙质隔层、含泥质纹层的致密砂岩及砂泥渐变段展布特征，并建立相应的地质模型；开展长7烃源岩生烃增压、油气突破不同隔层至储层的物理模拟及数值模拟等研究，明确生烃动力与隔层阻力的关系，揭示源储间不同类型隔层对陆相致密油成藏的控制因素，完善国内陆相致密油的理论基础。

目前认为致密油具有源储一体或近源大面积分布的成藏特征，但勘探实践表明，我国陆相致密油区普遍存在紧邻优质烃源岩的“甜点区”不含油甚至出大水的现象，因此需要对“甜点区”进行重新认识。该基金对国内源储间隔夹层的分类方案与成因认识进行了系统梳理；在大量岩心观察资料的基础上，将源储间隔夹层划分为泥质隔层、含泥质纹层致密砂岩以及砂泥渐变段三类，并分别对物性、展布以及测井响应特征进行综述。致密油成藏的主要动力为烃源岩生烃增压产生的“膨胀力”，当充注阻力大于膨胀力时，不利于原油成藏。定量表征显示，源储间隔夹层的厚度、横向连续性以及裂缝的发育情况共同控制着充注阻力的大小，影响着源储间隔夹层阻隔能力的强弱。基于此，建立了源储间隔夹层对致密油富集的四种控藏模式：（1）当源储间夹层厚度小于有效阻隔厚度L时，原油将突破隔挡继续运移；（2）当源储间夹层延伸半径小于波及区域半径r时，原油可从边缘地区突破，形成辐射状油气聚集带；（3）当源储间隔层厚度大于L且延伸半径大于r时，能够有效阻隔原油运移，造成局部“有砂无油”的现象出现；（4）当源储间隔夹层发育裂缝时，将会削减其隔挡能力，使原油能够较容易地突破。这些认识与模型完善了我国陆相致密油的理论基础，以期为我国陆相致密油勘探开发提供重要指导。