南海西科1井致密白云岩特征及成岩环境

西科1井为南海区域揭示生物礁地层最全、取心最为完整的钻井。该井下中新统三亚组发育致密白云岩，其孔隙度为1.65%～16.4%，平均6.7%。渗透率极低，局部渗透率仅为（11.8～39）×10−3 μm2，平均渗透率<1×10−3 μm2。利用沉积岩石学、岩石孔渗物性特征和包裹体测试方法，分析了致密白云岩的成岩特征，讨论了其成岩演化条件。致密白云岩中的白云石以粉晶、细晶和泥晶为主，形态多为自形和半自形，晶形较好，具有雾心亮边构造，白云石晶体接触紧密。晶间孔细小，孔隙呈分隔状且互不连通，次生溶蚀孔不发育。三亚组致密白云岩形成于准同生成岩阶段和后生成岩阶段。频繁的海平面变化和沉积物暴露，导致多期的海水充注孔隙作用，加上高温高盐的古海洋和地层环境，为致密白云岩的形成创造了条件。

CHARACTERISTICS AND DIAGENETIC ENVIRONMENT OF TIGHT DOLOSTONE IN WELL XIKE 1 , SOUTH CHINA SEA

Well Xike-1 is the most complete coring well to reveal the reef formation in the South China Sea. Tight dolostone is developed in the Miocene Sanya Formation, with porosity of 1.65% ～16.4%, and an average of 6.7%. The local permeability is only (11.8～39)×10−3 μm2, and the average permeability is less than 1×10−3 μm2. Based on sedimentary petrology, petrophysical properties of porosity and permeability and inclusion testing methods, the diagenetic characteristics of tight dolostone are analyzed, and the diagenetic evolution conditions are discussed. The dolomite in the tight dolostone is mainly composed of powder crystal, fine crystal and mud crystal. The morphology of dolomite is mostly euhedral and subhedral. The crystal shape is good, with fog center and bright edge structure. The dolomite crystal contacts closely. The intergranular pores are fine, separated and disconnected, and the secondary corrosion pores are not developed. The tight dolostone of Sanya Formation was formed in the stage of syngenetic and post genetic rocks. Frequent sea-level changes and sediment exposure lead to multi-stage seawater filling porosities, coupled with high temperature and high salinity paleo marine and stratigraphic environment, which create conditions for the formation of tight dolostone.