Quantitative Characterization and Genesis Analysis of Complex Modals of Pore Structure in Alluvial-Fan Sandy Conglomerate Reservoirs

新疆油田冲积扇砂砾岩储层岩石类型多样,颗粒大小混杂,分选极差,储层孔隙结构具有典型的多种模态特征,即单模态、双模态与复模态等。利用铸体薄片、压汞、恒速压汞资料定量表征了七东1区砂砾岩储层复杂模态孔隙特征以及连通特征,利用多元回归分析法建立复杂模态孔隙结构储层的识别模型。以此为基础,分析了冲积扇砂砾岩储层孔隙结构复杂模态成因机制。研究表明:单模态储层主要以Ⅰ类储层为主,双模态储层以Ⅱ、Ⅲ类储层为主,复模态储层以Ⅲ类储层为主。从单模态类型到复模态孔喉组合类型,孔隙发育由好变差,由连通较好的网状到连通较差的星点状,面孔率降低,平均孔径减小,孔喉配位数减小。利用已有147块样品统计发现,七东1区下克拉玛依组储层中单模态储层占19%、双模态储层占48%、复模态储层占33%。由此提出不同模态判断标准,建立了储层孔隙结构预测模型,揭示了储层构型、成岩后作用及注水(聚)开发中后期的系列变化等多因素是导致形成复杂模态的原因。

In the alluvial fan sandy conglomerate reservoirs in Xinjiang Oilfield, there existed various types of rocks, various sizes of grains and very poor sorting, so the reservoir pore structure had features of multiple kinds of modal, including unimodal, bimodal and multimodal. In this study, the multi- modal pore feature and connectivity of sandy conglomerate reservoirs in Block Qidong I were quantitatively characterized by using cast thin section, mercury injection and rate-controlled mercury penetration data first, then identification model for multimodal pore structure reser- voirs was established by using multiple regression analysis; on this basis, the causes of the multi- modal pore structure in the alluvial fan conglomerate reservoirs were analyzed. The study shows that the unimodal reservoirs are mainly Class I, bimodal reservoirs are mainly Class II and UI, and multimodal reservoirs are mainly Class ]TL With pore-throat combination turning from un- imodal to multimodal, the pore development degree turns from good to poor one, and from net- work shape of fairly good connectivity to star shape of poor connectivity, surface porosity is re- duced, and average pore size and pore-throat coordination number are declined. The statistics of 147 samples shows that the unimodal reservoirs account for 19%, bimodal reservoirs account for 48%, and multimodal reservoirs are 33% of the total reservoirs in Lower Karamay Formation of Block Qidong I. Based on the study, the criterion for reservoir modal judgement is proposed and the model for pore structure prediction is established; it is revealed that the reservoir types, the post-diagenesis and water （polymer） injection at the late stage of oilfield development and the other variation factors are the causes inducing the complex reservoir modals.