多期石油充注对深层碎屑岩储层外源碳酸盐胶结作用影响机理研究

Deeply buried clastic reservoirs are significant targets for oil and gas exploration in China. The genesis of high-quality reservoirs is crucial for petroleum exploration in deep layers. The influnce of petroleum emplacement on diagenesis exerts a major control on the formation of deeply buried high-quality reservoirs. Researches on clastic reservoirs in deeply buried layer and physical simulation experiments will be combined in this study. Firstly, the pore-throat structure, wettability, features of carbonate cements and the alternate relationship of carbonate cementation and petroleum emplacement in deeply buried clastic reservoirs of Es4x in Minfeng Sag, Dongying Depression, will be systematically studied. Secondly, some simulation experiments will be conducted in atmospheric pressure glass-bead models and core samples with the temperature and pressure of the geological conditions in order to discuss the influence of multi-stage petroleum emplacement on exogenous carbonate cementation. Thirdly, based on the results of the case study and the simulation experiments, we will focus on discussing the following two aspects, (1) the seepage characteristics and distribution heterogeneity of oil and water in micro-pores during the processes of multi-stage petroleum emplacing the reservoirs with heterogeneity of throat-pore and wettability, and (2) the influence of distribution heterogeneity of oil and water and its evolution on precipitation processes of exogenous carbonate cementation. Finally, the influencial mechanisms of multi-stage petroleum emplacement on exogenous carbonate cementation in deeply buried clastic reservoirs will be understood. The results will improve the theories of the impact of petroleum emplacement on diagenesis in clastic reservoirs, and provide guidance for understanding of formation mechanism of high-quality clastic reservoirs in deeply buried layers.

深层碎屑岩储层已成为我国油气勘探的重要接替领域。优质储层成因是制约深层油气勘探的关键因素，石油充注对成岩作用的影响是控制深层碎屑岩优质储层形成的主要因素。本项目采用深层碎屑岩油气储层实例解剖和物理模拟实验相结合的方法，基于东营凹陷民丰洼陷北带沙四段深层碎屑岩储层孔喉结构、润湿性、碳酸盐胶结物特征及碳酸盐胶结-石油充注序列的精细研究，开展多期石油充注对常压玻璃珠模型和地层温压条件下岩心样品中外源碳酸盐胶结作用影响的物理模拟实验，探讨多期石油充注过程中孔喉非均质性和润湿非均质性约束下的微观孔隙中油水渗流特征和分布非均质性，以及油水分布非均质性及演化对外源碳酸盐胶结物沉淀过程的影响；最终明确多期石油充注对深层碎屑岩储层中外源碳酸盐胶结作用影响机理。研究成果能够完善石油充注对碎屑岩储层成岩作用影响的基础理论，为深层碎屑岩优质储层成因机制研究提供理论基础。

石油充注对外源碳酸盐胶结作用的影响是石油地质领域长期争论的热点问题。本次研究以东营凹陷民丰洼陷北带沙四段储层为研究对象，运用薄片观察、阴极发光、包裹体分析、原位元素及同位素分析等测试手段，明确了碳酸盐胶结物的来源及成因，建立了碳酸盐胶结-石油充注序列。将深层碎屑岩储层实例解剖与物理模拟实验相结合，阐明了多期石油充注对碳酸盐胶结作用的影响机理。东营凹陷民丰洼陷北带沙四段储层主要发育铁方解石及铁白云石胶结物，两种碳酸盐胶结物具明显的外源特征。与砂岩垂向紧邻的泥岩及侧向紧邻的烃源岩中蒙脱石向伊利石转化为砂岩储层内铁碳酸盐胶结物提供Ca源。烃源岩中有机质脱羧及碳酸盐岩屑溶解为储层中铁碳酸盐胶结物提供C源。砂岩储层中两期石油充注与碳酸盐胶结作用序列为：白云石胶结-黄色荧光油充注-铁方解石与铁白云石胶结-蓝色荧光油充注。孔喉结构及润湿非均质性导致微观孔隙中油水渗流过程及分布存在非均质特征，控制了外源碳酸盐沉淀过程及发育位置。第一期石油充注过程中，早期碳酸盐胶结物与油分子之间的静电力及油分子与油分子之间的相互作用力使石油运移路径向早期碳酸盐胶结物表面偏移，导致含有较多大孔隙且适量白云石胶结物的储层更有利于发生第一期石油充注。孔隙结构及润湿性非均质性共同控制下的油水分布非均质性导致外源物质在含水连通孔隙及水膜中以平流或扩散的方式继续运移并沉淀晚期碳酸盐胶结物，而在充油孔隙中物质搬运及碳酸盐胶结作用被抑制。在第一期石油充注程度较大的砂岩储层中，虽然晚期碳酸盐胶结作用可以继续进行，但是相比于第一期石油充注程度较低的砂岩储层，晚期碳酸盐胶结物的含量明显减少。第一期充注的石油及油润湿碳酸盐胶结物降低了孔隙突破压力，导致第一期石油充注程度较高且含有适量碳酸盐胶结物的储层更有利于发生第二期石油充注。烃类充注与碳酸盐胶结作用的相互协同作用共同控制着优质储层的形成及成藏过程。