中东地区孔隙型碳酸盐岩储层渗透率主控因素分析

Key controlling factors of permeability in porous carbonate reservoirs of Mishrif Formation in the Middle East

碳酸盐岩储层非均质性极强,孔喉结构复杂,且孔隙度与渗透率相关性差。中东地区白垩系Mishrif组发育典型的孔隙型碳酸盐岩储层,相同孔隙度条件下渗透率相差达3个数量级,给准确评价该类储层的渗透能力以及合理的储层分类带来了极大挑战。为深入分析中东地区Mishrif组孔隙型碳酸盐岩储层渗透率的主控因素,基于M油田415个高压压汞实验样品数据统计对比,明确了研究区Mishrif组碳酸盐岩储层具有多种模态并存的孔喉结构特征,其中单模态孔喉结构储层的孔渗相关性明显好于双模态和多模态孔喉结构储层;进而对孔喉结构特征参数进行定量分析,明确多模态孔喉结构碳酸盐岩储层孔隙度和渗透率随孔喉结构参数变化的规律。研究表明,汞饱和度为20%对应的孔喉半径(R20)与渗透率的相关性最好,将R20作为特征孔喉半径与孔隙度和渗透率进行相关性分析发现,随着孔喉半径的增加,孔隙度先线性增加,至一定程度后维持稳定不再增加,与之形成对比的是随着R20的增加,渗透率持续增加。

Carbonate reservoirs are characterized by strong heterogeneity and complex pore throat structures,with poor cor⁃relation between porosity and permeability.Typical porous carbonate reservoirs develop in the Cretaceous Mishrif Forma⁃tion in the Middle East,with the permeability differing by three orders of magnitude under the same porosity,bringing a huge challenge to accurately evaluate permeability and properly categorize reservoirs.To deeply analyze the key controlling factors of permeability in porous carbonate reservoirs of the Mishrif Formation in the Middle East,we find different models of pore throat structures coexist in the carbonate reservoirs of the research area through 415 MICP samples from the M Oil⁃field.To be specific,porosity and permeability correlate much better in a uni-modal pore throat structure than in bi-modal and multi-modal structures.Then the characteristic parameters of pore throat structures are analyzed quantitatively to ex⁃plain the regularity in porosity and permeability of carbonate reservoirs with a multi-modal pore throat structure when the parameters of the pore throat structure are changed.Results demonstrate that the pore throat radius(R20),corresponding to 20%mercury injection saturation,correlates best with permeability.With R20 as the characteristic pore throat radius,its correlation study with porosity and permeability reveals that porosity first increases linearly with the greater R20 and then remains stable,while permeability keeps rising with the growth in R20.