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