苏里格气田东二区砂岩成岩作用与致密储层成因

鄂尔多斯盆地苏里格气田东二区主力气层储层岩性致密,成为制约该区天然气勘探开发的主要因素。为了查明储层物性变差的主要原因,利用砂岩薄片、铸体薄片、扫描电镜、X射线衍射分析等实验手段,深入研究了对苏里格气田东二区主力气层二叠系山西组山1段、石盒子组盒8段储层砂体的岩石学特征与成岩作用。研究发现,储层砂体以岩屑砂岩、岩屑石英砂岩为主,砂岩成熟度较低;研究区砂岩成岩作用主要有压实作用、胶结作用、溶蚀作用和交代作用。结论认为:成岩作用达到中成岩阶段B期;早成岩的压实作用是孔隙度降低的主要原因之一;中成岩期A期在酸性介质条件下由溶蚀作用形成的次生孔隙对砂岩的储集性能具有明显的改善作用;中成岩B期的胶结作用是储层物性变差的最主要原因。

Diagenesis of Sandstone and Genesis of Compact Reservoirs in the EastⅡ Part of Sulige Gas Field,Ordos Basin

Based on the experimental methods of slice identification,casting slice,scan electron microscope and X-ray diffractions,characteristics of petrology and diagenesis on reservoir in Shan1 section of Shanxi Formation and He 8 section of Shihezi Formation of Permian system in the east Ⅱ part of Sulige gas field were studied.The result shows that the main lithology of sandstone in this area is dominated by lithic sandstone and lithic silicarenite with low grade of maturity.Diagenesis of sandstone in this area mainly include compaction,cementation,corrosion and alteration.Diagenetic minerals mainly include siliceous mineral(chalcedony,quartz secondary overgrowth,and authigenic quartz small crystal),clay minerals(chlorite,illitesmectite formation,kaolinite,illite) and carbonate minerals(calcite,ferrocalcite,ankerite) etc.The highest diagenetic stage reach to period B of middle diagenetic stage on the basis of maturity of organic matter,diagentic minerals,homogenisation temperature of fluid inclusion etc.diagenetic symbols.Diagenesis of sandstone in the east Ⅱ part of Sulige gas field underwent syndiagenetic stage,early diagenetic stage and middle diagenetic stage.Diagenetic environment succession went through faintly acidic environment in period A of early diagenetic stage,relative highly acidic environment in period B of early diagenetic stage,highly acidic environment in period A of middle diagenetic stage,and faintly alkaline environment in period B of middle diagenetic stage. Fast decreasing of porosity could be seen in evolution curve of porosity caused by cementation from period B of early diagenetic stage to period A of middle diagenetic stage. The early diagenetic compaction is one of main factors to decreasing porosity of Shan1 section of Shanxi Formation and He 8 section of Shihezi Formation by means of quantitative calculation.Cementation is the most important factor to decreasing porosity in the studied area.Cementation in period B of middle diagenetic stage is the most important factor leading to poor physical property of sandstone reservoirs especially.The secondary pore formed by corrosion in acidity medium condition in period A of middle diagenetic stage can distinctly ameliorate poor reservoir capability of sandstone.Consequently,erosion play a key role in promoting of physical property of sandstone reservoirs in the east Ⅱ part of Sulige gas field.Secondary pore formed by corrosion of calc-alkali volcanics rock,feldspar and calcite cements in acidity medium condition in period A of middle diagenetic stage is main reserving space in the studied area.Corrosion of quartz particle was discovered in this area for the first time,which implies properties of fluid medium transferred gradually from acidity to alkaline since period B of middle diagenetic stage.