基于电成像的孔洞型碳酸盐岩储层连通性评价

Evaluation of Pore-Type Carbonate Reservoir Connectivity Based on Electrical Imaging

碳酸盐岩储层非均质性强,孔隙结构复杂,相较于常规碎屑岩储层,其孔隙度、渗透率关系的规律及特征不明显。碳酸盐岩储层的连通性与孔洞特征具有强相关性,且连通性是影响储层渗透率的重要因素,因此,对碳酸盐岩孔洞连通性的评价是孔洞型碳酸盐岩储层评价的关键问题。以伊拉克东南部B油田FQ-1井M组MB21亚油组孔洞型碳酸盐岩储层为例,基于地层微电阻率扫描成像(FMI)测井的高分辨率动态图像,利用最大类间方差算法(OTSU)进行二次迭代分割,识别电成像图像孔洞;根据8连通域标记法标记连通孔洞;提取每个连通孔洞的特征孔径、内部最长通道距离、内部最长通道与水平方向夹角、平均通道宽度这4个几何参数,最终构建孔洞型碳酸盐岩储层连通指数。连通指数在伊拉克东南部B油田FQ-1井M组MB21亚油组孔洞型碳酸盐岩储层的应用表明,利用此方法建立的连通指数与FQ-1井碳酸盐岩储层岩心渗透率相关系数达0.8437,并且连通指数曲线的趋势符合岩心渗透率在储层不同深度的分布情况,证明了连通指数可以指示储层孔隙结构较好、溶蚀孔洞发育的深度段,并可以划分储层中连通性较好的深度区间,该参数对于寻找碳酸盐岩储层渗透层具有重要意义。

Compared with conventional clastic rock reservoir,carbonate rock reservoir has less porosity and permeability relationship,because of its strong heterogeneity and complex pore structure.There is a strong correlation between the connectivity of carbonate reservoirs and the characteristics of pore,and the connectivity is an important factor affecting the permeability of reservoirs.Therefore,the evaluation of the connectivity of pore-type carbonate reservoirs is the key issue in the evaluation of carbonate reservoirs.Taking the pore-type carbonate reservoir of FQ-1 well M group MB21 suboil group in B oilfield in southeast Iraq as an example,based on the high-resolution dynamic image of formation microscanner image(FMI)logging,the maximum inter-class variance algorithm(OTSU)is used for the second iteration segmentation to identify the pores,and then the connected pores are labeled according to the 8-connected component labeling method.Then,four geometric parameters,namely,characteristic aperture,distance of the longest internal channel,angle between the longest internal channel and horizontal direction,and average channel width of each connected pore,are extracted to construct the connectivity index of the pore-type carbonate reservoir.The application of the connectivity index in the pore-type carbonate reservoir of MB21 suboil group of FQ-1 well M group in B oilfield in southeast Iraq shows that,the correlation coefficient between the connectivity index established by this method and the core permeability of the carbonate reservoir in FQ-1 well is 0.8437,and the trend of the connectivity index curve is consistent with the distribution of core permeability at different depths of the reservoir.It is proved that the connectivity index can indicate the reservoir depth segment with good pore structure and dissolution pore development,and can divide the depth segment with good connectivity in the reservoir.Therefore,this parameter is of great significance for searching the permeability layer of carbonate reservoir.