陕甘宁盆地中部马五段上部成岩层序地层学研究及其意义

A Study of Diagenetic Sequence Stratigraphy of Upper Ma 5 Member, Central Ordos Basin and Its Significance

陕甘宁盆地具有较有利的成岩层序地层学研究条件。根据多种资料 ,将盆地中部马五段上部划分出八个准层序。准层序内部的酸不溶物含量、自然伽玛曲线、稳定碳同位素值及残余含盐量等参数呈现规律性变化 ,这为相似类型地层的准层序划分提供了新的方法。在不同的成岩作用中 ,准层序上部的溶解作用 /去膏化作用明显强于准层序下部 ;准层序上部多为准同生白云岩化形成的泥 -粉晶白云岩 ,下部则多为再次云化形成的细粉晶 -粗粉晶白云岩 ;压溶作用形成的缝合线在层组底部的出现概率远大于层组上部。研究发现 ,暴露型准层序界面的平均孔隙度与层序界面的平均孔隙度相差不大 ,表明暴露型准层序界面对形成和保存孔隙的贡献可能比层序界面更大 ,应受到足够的重视。多套平行叠置发育良好的暴露型准层序界面应是油气的良好赋存场所。

Ordos basin has favorable condition for the research work. On the basis of various sorts of data, 8 parasequences were identified in Upper Ma 5 Member of the basin. Within each parasequence, content of substances indissoluble in acid, content of remnant gypsum, δ 13 C values and NG logging curve display regular changes, indicating the controlling role of sea_level fluctuation. These parameters can provide new methods for the division of paresequence boundaries. Among differnet diageneses, dissolution in the upper part of each parasequence is stronger than that in the lower part. In most parasequences, dolomite in the lower part seems coarser than that in the upper part, and within most beddings pressure solution also occurs more likey at the bottom than in the upper part. It is discovered that the average porosity of exposed parasequence boundaries is similar to that at sequence boundaries, suggesting the larger contribution of parasequences boundary to the preservation of porosity than sequence boundary. Hence the exposed parasequence boundaries deserve more attention. If overlapped, a set of exposed parasequences boundaries would definitely become wonderful reservoirs for oil and gas.