自生绿泥石对储集层质量影响的定量评价:以北部湾盆地涠西南凹陷涠洲组三段为例*

为了定量研究自生绿泥石对储集层质量的影响,在限定控储因素前提下,通过常规岩心分析、扫描电镜、薄片鉴定、激光粒度分析和黏土矿物X衍射等资料,以北部湾盆地涠西南凹陷涠洲12-X油田古近系涠洲组三段碎屑岩储集层为例,探讨了自生绿泥石对石英次生加大、孔隙结构及储集层物性的影响,并提出了综合得分评价法,定量评价自生绿泥石对储集层物性的控制作用。研究结果表明,当溶蚀作用积极意义大于绿泥石沉淀的消极影响时,石英加大和方解石含量较高(7.3%)及自生绿泥石相对含量较低(20%~30%)的细砂“控孔喉”作用,等同于石英加大和方解石含量较低(2.4%)及自生绿泥石含量较高(30%~40%)的细砂,二者的“控孔喉”作用具有互补性。自生绿泥石的“控孔、控渗”作用与碎屑颗粒粒度、分选、胶结物及泥质含量等因素的“控孔、控渗”作用相互制约,存在互补性和差异性,绿泥石相对含量较低的中砂“控孔、控渗”作用等同于绿泥石相对含量较高的细砂(互补性);泥质含量较低的细砂岩中绿泥石“控孔、控渗”作用弱于泥质含量较高的细砂岩(差异性)。总之,在岩相一定的情况下,包膜或衬里状绿泥石与孔渗呈正相关关系,孔隙充填状绿泥石与孔渗呈负相关关系。

Quantitative evaluation of impact of authigenic chlorite on reservoir quality: a case study of the Member 3 of Weizhou Formation in Weixinan sag,Beibu Gulf Basin

In order to quantitatively study the impact of authigenic chlorite on reservoir property, different analytical results, including conventional core analysis, scanning electron microscopy, thin section identification, laser particle size analysis and clay mineral X-ray diffraction, were used to illustrate the impact of authigenic chlorite on quartz overgrowth, pore structure and reservoir property under the limited controlling factors of reservoir,taking the reservoir of the Member 3 of Paleogene Weizhou Formation in Weizhou-12-X oilfield in Weixinan sag, Beibu Gulf Basin as an example. The comprehensive score evaluation method is put forward to quantitatively evaluate the controlling effect of authigenic chlorite on reservoir physical property. The results show that the “controlling pore throat” effect in fine sandstone with low chlorite content(20%~30%)and high quartz overgrowth and calcite content(7.3%)is equivalent to that of fine sandstone with high chlorite content(30%~40%)and low quartz overgrowth and calcite content(2.4%)when the rock dissolution is stronger than the chlorite precipitation, and their “controlling pore throat” effects are complementary. The “controlling porosity and permeability” effect of authigenic chlorite restrict with other factors (e.g., grain size, sorting, contents of cement and clay), which shows complementarity and difference. The “controlling porosity and permeability” effect of medium-grained sandstone with relative low chlorite content is equivalent to the fine-grained sandstone with relative high chlorite content. The “controlling porosity and permeability” effect of authigenic chlorite in the fine-grained sandstone with low clay content is weaker than that of the fine-grained sandstone with high clay content. In short, for a given lithofacies, there is a positive correlation between the contents of coated or lined chlorite and porosity and permeability, while it shows a negative correlation between the content of pore filling chlorite and porosity and permeability.