泥页岩埋藏过程孔隙度演化与预测模型探讨

Evolution and Models of Shale Porosity During Burial Process

统计分析了国内外大量实测及测井解释孔隙度数据,揭示泥页岩孔隙度演化规律,指出孔隙度变化过程的差异,划分出正常压实和欠压实孔隙演化区。从3个方面探讨了引起孔隙度差异的原因:①处于生油高峰期的优质烃源岩,生烃过程中产生的超压减缓了孔隙度变小的速率,是泥页岩在中深层还保持相对较大孔隙度的主要因素,超压贡献的孔隙度超过5%;②处于生气中晚期的优质烃源岩,生烃过程形成的有机质纳米孔隙是深层富含有机质泥页岩孔隙度增加的另一个重要因素,有机质纳米孔贡献泥页岩孔隙度达到1.8%;③有机酸对脆性矿物的溶蚀作用对泥页岩孔隙增大贡献比预想的小。根据以上认识,建立了3段式的正常压实模型、欠压实模型以及有机质纳米孔校正模型,分析了模型关键参数,提出了有机质面孔率的估算模板。应用实例证明这些模型具有实用价值,可促进页岩气、页岩油等非常规油气资源评价及勘探开发技术的发展。

Through the analyses of shale porosity data from core test and logging interpretation, this paper demonstrates the shale porosity evolution trend and points out the difference of porosity evolution between normal compaction and under-compaction. Three reasons which caused difference in porosity evolution are discussed. （1）For the high quality shale during oil generation peak,the over-pressure which was generated during hydrocarbon generation slows down porosity decline rate, which is the main factor explaining why shale remains relatively high porosity at middle-deep depth. Over 5 ~ of porosity increment was contributed by over-pressure. （2）For the high quality shale during middle-late gas generation period, nano-pores origi- nated in hydrocarbon generation processes is another important factor causing the increment of porosity in organic-rich shale,which contributes 1.8% in average to the porosity evolution in shale. （3）The organic acid dissolution affects less to shale porosity increment. Based on the conclusions above, we have built three-stage normal compactionmodel, under-compaction model and nano-pore originating in organic matter correction model,analyzed the key parameters of the model and proposed a template for estimation of the face pore ratio in organic matter.