Quantitative evaluation of the carbonate reservoir heterogeneity based on production dynamic data: A case study from Cretaceous Mishrif formation in Halfaya oilfield, Iraq

Abstract

Reservoir heterogeneity greatly affects the reservoir production ability. The heterogeneity in a carbonate reservoir is extremely serious. To provide an accurate description of the reservoir production ability, it is essential to quantitatively characterize and evaluate the carbonate reservoir heterogeneity. However, the evaluation criteria of carbonate reservoir heterogeneity are still unclear and hard to reflect the effect of the reservoir heterogeneity on oil and gas production. In this study, we developed an approach to quantitatively evaluate both the intermediate heterogeneity (i.e., the heterogeneity in a layer) and interlayer heterogeneity in a carbonate reservoir by comparing the heterogeneity characterization parameters with dynamic production data. The developed evaluation criteria can reflect the effect of the reservoir heterogeneity on oil and gas production and can be readily adopted in oilfield. The heterogeneity characterization parameters used are the permeability variation coefficient, permeability dart coefficient, and permeability contrast coefficient, respectively. The dynamic production data are required to be firstly split to obtain the production rate of a single layer. A case study from Mishrif formation in Halfaya oilfield is conducted. Based on the newly developed method, the intermediate heterogeneity of the study region is divided into three types, i.e., the homogeneous, weak heterogeneous, and strong heterogeneous types. While the interlayer heterogeneity is divided into two types, i.e., the weak and strong heterogeneous types. In this case study, the permeability variation coefficient is the best choice to describe the effect of heterogeneity on oil production among the three heterogeneity characterization parameters. Therefore, the planar distributions of intermediate heterogeneity for each small layer and that of interlayer heterogeneity for Mishrif formation in the study region are generated based on the permeability variation coefficient. Based on the developed evaluation criteria, we can find that the intermediate heterogeneity of most layers belongs to the weak and strong heterogeneous types. Moreover, the interlayer heterogeneity of the study region belongs to the strong heterogeneous type. By comparing the distributions of reservoir heterogeneity and sedimentary microfacies, we can conclude that the reservoir heterogeneity is strong in the area where multiple sedimentary microfacies exist, while it is weak in the area controlled by a single sedimentary microfacies. • An approach to quantitatively evaluate both the intermediate heterogeneity and interlayer heterogeneity in a carbonate reservoir is developed by comparing the heterogeneity characterization parameters with dynamic production data. • The developed evaluation criteria can reflect the effect of the reservoir heterogeneity on oil and gas production and can be readily adopted in oilfield. • The reservoir heterogeneity is strong in the area where multiple sedimentary microfacies exist, while it is weak in the area controlled by a single sedimentary microfacies.