川中高石梯台缘带灯四段白云岩储层岩石物理模型研究

Petrophysical model for dolomite reservoirs:A case study in the fourth member of the Dengying formation at a platform margin in the

(1.长江大学地球科学学院,湖北武汉 430100;2.长江大学四川盆地研究中心,湖北武汉 430100;3.中国石油西南油气田分公司勘探开发研究院,四川成都 610041)

(1.School of Geosciences,Yangtze University,Wuhan 430100,China;2.Research Center of Sichuan Basin,Yangtze University,Wuhan 430100,China;3.Research Institute of Exploration and Development,PetroChina Southwest Oil & Gas Field Company,Chengdu 610041,China)

四川盆地中部高石梯地区灯四段储层的发育及储集性能受白云岩中硅质含量的影响,与硅质白云岩相似的储层岩石物理特征给储层预测带来了极大的困难。针对该区白云岩中存在的结构特征复杂的硅质矿物成分,利用一种能够准确描述硅质矿物与储层的岩石物理模型来辅助预测有效储层。该预测方法将硅质矿物视为一种固体包含物,利用固体替换的方式求取岩石的基质弹性模量以描述硅质矿物结构特征,然后综合利用Kuster-Toksz(KT)模型、DEM模型、Gassmann方程和Wood方程构建新的岩石物理模型,在纵波速度约束下利用新的岩石物理模型反演各种孔隙的体积分数和硅质矿物的(形状)等效纵横比参数。实际应用结果表明,采用新方法求取的横波速度曲线形态、偏差程度和相关性明显好于利用Xu-Payne模型和前人针对复杂缝洞储层模型求取的结果,验证了该方法的适用性和有效性。该方法能够更好地描述矿物结构特征,为四川盆地中部高石梯地区后续储层响应特征分析及储层预测工作提供了依据。

In the Gaoshiti area of the central Sichuan Basin,siliceous minerals are widely distributed in the dolomites of the Dengying Formation.Research shows that the amount of siliceous minerals is inversely correlated with the abundance of reservoirs.Moreover,the siliceous minerals all share similar petrophysical characteristics.Evidently,a rock model is needed for an effective reservoir prediction,to accurately describe the relationship between the dolomite reservoirs and the characteristics of siliceous minerals.However,achieving a description of these minerals using existing petrophysical models is challenging as these models use averaging techniques to calculate the mineral abundances,resulting in misunderstandings on the mineral structures,and thus in incorrect rock physical parameters.Consequently,substantial difficulties arise in reservoir prediction.To overcome this issue,a novel method was proposed.In the proposed method,silica is regarded as a type of solid inclusion with independent aspect ratio parameters.A new petrophysical model was constructed by combining the solid replacement equation,Kuster–Toksz model,DEM model,Gassmann equation,and Wood equation.Using the new model,the volume fraction of pores and the aspect ratio of the siliceous minerals were obtained under a constrained P-wave velocity.Subsequently,the shear wave velocity was also obtained.The proposed method was validated on actual well data from the study area.The results showed that the shape,deviation,and correlation of the shear wave velocity curve obtained by the proposed method were superior to those obtained via traditional models,thereby confirming the applicability and effectiveness of the proposed method for silica-dolomites with complex structural characteristics.Furthermore,the proposed approach can describe the error caused by incorrect mineral structure characteristics,providing a basis for subsequent reservoir response analysis and reservoir prediction,and a reference for the evaluation of complex mineral structure characteristics.

国家自然科学青年基金项目“富有机质页岩岩石物理与AVO响应模式研究”(41804120)资助。

10.3969/j.issn.1000-1441.2021.06.012