岩石结构对碳酸盐岩储层构造缝发育的影响机理

Influence Mechanism of Rock Structure on the Development of Structural Fractures in Carbonate Reservoir

明确裂缝发育的主控因素对于油田井网部署及调整具有重要意义。但粒度和孔隙度对构造缝发育影响机理的研究中仍旧存在一些争议。系统梳理了岩石粒度和孔隙度两个因素对裂缝发育的影响的争议,综合前人实验分析数据及有限元分析方法,分析了岩石结构对碳酸盐岩构造缝发育的影响机理,建立了新的裂缝发育影响因素解释模型,并基于该模型进一步探讨了成岩作用对碳酸盐岩构造缝发育的影响。结果表明,随着岩石粒度增大,不同学者对岩石是否更容易发育裂缝存在完全相反的分析结果。随着孔隙度增大,岩石强度降低,对于岩石更难以发育裂缝的矛盾现象尚缺少合理的解释。岩石是否易于发育裂缝取决于岩石强度和岩石刚度两种因素的相对变化,两种因素符合幂律指数关系,指数函数的幂的值决定了岩石是否更容易发育裂缝。随着粒度的增大,岩石弹性模量减小速度比岩石强度的减小速度可能更大,则岩石更难发育裂缝,亦可能更小,则岩石更易发育裂缝。随着孔隙度的增大,岩石弹性模量减小速度大于岩石强度减小速度,岩石更难以发育裂缝。基于本次提出的岩石强度和岩石弹性模量双重因素控缝理论不仅可成功解释成岩作用对裂缝发育的影响,对于进一步深化对裂缝形成机理认识也具有重要指导意义。

Understanding the controlling factors of fracture development is of great significance for oilfield well pattern deployment and adjustment.However,there are still some controversial issues in the study of the mechanism of the impact of grain size and porosity on the development of structural fractures.The controversy over the influence of two factors,rock grain size and porosity,on fracture development was summarized.Based on previous experimental analysis data and finite element analysis methods,the influencing mechanism of rock structure on the development of carbonate structural fractures was analyzed,a new interpretation model for the factors affecting fracture development was established,and the impact of diagenesis on the development of carbonate structural fractures based on the new model was discussed.The results show that with the increase of rock grain size,different scholars have completely opposite analysis results on whether rocks are more prone to develop structural fractures.As porosity increases and rock strength decreases,there is still a lack of reasonable explanation for the contradictory phenomenon that rock is more difficult to develop structural fractures.Whether a rock is easy to develop structural fractures depends on the relative changes of two factors,rock strength and rock stiffness,which conform to a power law exponential relationship.The value of the power of the exponential function determines whether a rock is more likely to develop structural fractures.With the increase of particle size,the decrease rate of rock elastic modulus may be greater than the decrease rate of rock strength,making it more difficult for the rock to develop structural fractures,vice verse,the rocks are easier to develop structural fractures.With the increase of porosity,the elastic modulus of rock decreases faster than the strength of rock,making it more difficult for rock to develop structural fractures.The dual-factors-fracture-control theory based on rock strength and rock elastic modulus proposed can not only successfully explain the impact of diagenesis on fracture development,but also have an important guiding significance for further deepening the understanding of fracture formation mechanism.