Abstract
Geological modeling is very important in reservoir study, where it is described the framework of the structure and provided a distribution of petrophysical properties, the geological model helps to comprehend the fluid flow behavior affected by the heterogeneity of reservoir, also it is used to calculate oil initially in place and to choose the new well location in reservoir management. In this study, a geological model is built for Nahr Umr Formation based on data of 11 wells (SU-2, SU-3, SU-4, SU-5, SU-6, SU-7, SU-9, SU-10, SU-11, SU-13, and SU-14), including the location of wells, well tops, also contour map of the Nahr Umr Formation in Subba oil field is utilized. The structural model is constructed for the Nahr Umr Formation, which consists of two domes. The formation is composed of sandstone mainly interbedded with shale. The formation is divided into four units (B1, B2, C1, and C2) depending on well log data, each unit is divided into layers for getting better distribution of petrophysical properties, where unit B2 is divided to the number of layers is higher than other units due to its heterogeneity. The variogram is used as a geostatistical method to predict the petrophysical properties at unsampled locations, experimental variogram is calculated from well log data in a horizontal and vertical direction. The spherical variogram model shows a good fitting with the experimental variogram. Sequential Gaussian algorithm is used in distribution of petrophysical properties in a geological model which shows good petrophysical properties in unit B2 and unit B1, while units C1 and C2 are highly saturated with water.
Highlights
Geological modeling provides the distribution of petrophysical properties such as permeability, porosity and net pay, it is considered the basis on which the reservoir model is constructed
Experimental variogram is calculated for vertical and horizontal direction, while all direction must be considered in the variogram to comprehend the behavior of the variogram, the experimental variogram must fit with the specific positive definite functions such as gussian, exponential, and spherical variogram models
The experimental variogram shows high fitting with Spherical model after examining the models that are provided by the simulator
Summary
Geological modeling provides the distribution of petrophysical properties such as permeability, porosity and net pay, it is considered the basis on which the reservoir model is constructed. Several researchers were interested in studying the reservoir oil fields using geostatistical analysis and variogram, among the important researches in this field are: Sahin et al (1998) used the sequential Gaussian and kriging simulation to get maps for porosity and permeability in carbonate reservoir, eastern Suadi Arabia. They applied cross-validation in the generated modeling. Amanipoor et al, (2013) use static modeling to analyze properties of Bangestan oil reservoir They employed the petrophysical data to prepare the 3D model, and variogram to specify the spatial correlation. The purpose of geological modeling is to evaluate the petrophysical properties in the reservoir in order to estimate oil initially in place and provide useful information in developing oil field and the reservoir simulation studies
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