压实作用和胶结作用对鄂尔多斯长_8储层的影响

Effects of Compaction and Cementation on the Chang 8 Member Reservoir in the Ordos Basin

为探讨压实作用和胶结作用对鄂尔多斯盆地长_8储层孔隙度的影响,将长_8储层按区域分为5个体系,运用矿物岩石学和统计学方法对压实、胶结作用进行系统研究。对压实率、胶结率、孔隙度变化与压实-胶结作用的相关性进行定量计算。研究发现,压实作用具有早期快速埋深和埋藏时间长的特点;胶结作用发生于整个成岩过程,包括硅质和碳酸盐胶结。压实率统计表明,储层处于中等—强压实程度。压实作用造成的长_8~1层各体系孔隙度损失:东北>西北>南部>西南>西部;长_8~2层:西北>西部>西南>东北>南部。压实孔隙度损失平均大于19%。胶结率统计表明,储层为弱—中等胶结,胶结孔隙度损失在11%～16%。胶结作用造成的长1/8层各体系孔隙度损失:西部>东北>西北>南部>西南,长2/8层:东北>南部>西部>西南>西北。压实作用对孔隙度造成的损失比胶结作用大,是鄂尔多斯长_8储层物性的主要破坏作用。

To investigate the effects of compaction and cementation on the porosity of the Chang 8 Member reservoir in the Ordos Basin, the reservoir was divided into five systems according to their regions. Methods in mineralogy, petrology, and statistics were employed to systematically study compaction and cementation. The degree of compaction and cementation, porosity variations, and correlations between compaction and cementation were quantitatively calculated. The results demon- strate that compaction was characterized by early rapid subsidence and prolonged burial, while cementation, including silicon and carbonate cementation, occurred throughout the entire diagenesis process. Statistics for the degree of compaction indicate that the reservoir is moderately to strongly compacted. The porosity loss of each system due to compaction in the Chang81 Member vary in descending order as： northeast 〉 northwest 〉 south 〉 southwest 〉 west, whereas that of the Chang 82 Mem- ber vary as northwest 〉 west 〉 southwest 〉 northeast 〉 south. The porosity losses resulting from compaction are 〉 19 % on average. Statistics of the degree of cementation reveal that the reservoir is weakly to moderately cemented, and the porosity losses caused by cementation are in the 11%-16% range. The porosity loss of each system in the Chang 81 Member due to cementation vary in descending order as west 〉 northeast 〉 northwest 〉 south 〉 southwest, while that of the Chang 82 Member vary as： northeast 〉 south 〉 west 〉 southwest 〉 northwest. Compaction leads to greater porosity losses than cementation, and is the main destructive factor to physical properties of the Chang 8 Reservoir in the Ordos Basin.