Analytical Methods to Develop Accurate Structural Model for the Asmari Reservoir

Abstract

Crossing of Asmari can be a challenging endeavor in certain instances, particularly when dealing with structural complexities, compounded by the presence of a substantial layer of Gachsaran formation evaporates overlying the reservoir. The primary aim of this study was to establish a precise and comprehensive structural model for the Asmari reservoir. Utilizing geological logs for dip classification offers the advantage of directly depicting the structural origin. This approach helps in identifying the Asmari fault and fracture systems and their impact on production, ultimately resolving structural complexities. To investigate the reasons behind the intersection of the Kalhur member and the unexpected increase in the thickness of the Asmari formation, FMI data was acquired over the interval ranging from 1550m to 2065m. The analysis of picked bedding dips revealed abrupt variations in dip magnitude and azimuth reversals. These observations were pivotal in unraveling the structural intricacies of the reservoir. A significant fault was identified within zone five of the Kalhur member, and its interpretation suggests that it is a reverse fault. This conclusion is based on the observed dip pattern and the distinctive characteristics of the logs. Around the fault, the beds and layers exhibit elevated dips, largely attributed to the plastic nature of anhydrite and marly/shaly anhydrite within the formation. The anhydrite-indicator curve obtained from the FMI and gamma-ray logs provides further evidence that the well entered the Kalhur member after intersecting the major fault located within this particular zone. The interpretation of structural dip played a pivotal role in resolving structural complexities, leading to the precise determination of the well's location within the Asmari reservoir. This achievement was particularly critical as it enabled the well to reach the lower contact of the Asmari formation. This interpretation was facilitated by analyzing FMI images and petrophysical logs in well LL-26.