北黄海中生代残留盆地砂岩成岩作用及其对孔隙的影响

SANDSTONE DIAGENESIS IN MESOZOIC RESIDUAL BASIN OF NORTH YELLOW SEA AND ITS IMPACT ON POROSITY

北黄海盆地中生界为残留盆地,油气勘探难度大、程度低,勘探工作主要集中于盆地东部。根据砂岩铸体薄片、扫描电镜、X射线衍射、阴极发光、流体包裹体测温等多种分析测试手段,对中生界储层砂体的岩石学特征、成岩作用及对孔隙的影响进行了研究。结果表明,该区中生界砂岩岩性以长石砂岩、长石岩屑砂岩为主,成岩作用主要有压实作用、胶结作用、交代作用、溶蚀作用,胶结物有黏土矿物、碳酸盐和硅质,成岩作用阶段已达到中成岩A期,结合盆地构造演化建立了成岩演化模式。早期的机械压实作用和胶结作用使原生孔隙大量丧失,长石及碳酸盐的溶蚀能够部分改善储层物性。原生孔隙的大量丧失和次生孔隙发育程度较低是造成本区储层低孔、低渗的主要原因。

The Mesozoic basin of the North Yellow Sea is a residual basin.Current petroleum exploration was mainly focused on its east part.The petrology and diagenesis and its effect on porosity of the Mesozoic reservoir were studied in this paper through analyses of casting slice,scan electron microscope,X-ray diffraction,cathode luminescence,and fluid inclusions.Sandstones in this region are dominated by arkose and lithic-arkose cemented by clay minerals,carbonate and silicon.The sandstones have suffered from various kinds of diagenesis,such as compaction,cementation,alteration and dissolution,and reached the A-period of the middle diagenetic stage.A model of diagenesis was constructed in this paper with reference to the tectonic evolution of the basin.Original porosity was severely reduced under compaction and cementation in the early diagenetic stage.Porosity and permeability of reservoirs were partially improved by dissolution of feldspar and carbonate later on,but still kept at a low level.The low porosity and permeability of the sandstone reservoirs in this area were mainly caused by the losing of original porosity and the low secondary porosity.