Application of the Wellbore Imaging Tools in Tengiz Field

Abstract

This paper provides an overview of the borehole imaging tools (BIT) run in the Tengiz-Korolev field giant carbonate reservoirs located in Western Kazakhstan. Borehole imaging tools have historically been run in Tengiz-Korolev fields both wireline-conveyed and in logging-while-drilling (LWD) conditions. These tools provide indirect images that are derived from a high-density grid of electrical, ultrasonic and formation density measurements. Understanding the distribution of vugs and fractures in carbonate reservoirs greatly enhances the correctness of any proposed flow modeling and, through better plans for drilling and completion, improves production. There have also been successful attempts in generating core-like images based on high-resolution electrical resistivity data recorded in Tengiz's unique "non-conductive" oil-based mud environment. Validation of existing core data with resistivity image log-based fracture picks was performed and encouraged the log-based fracture characterization workflow at wells. Incorporation of the BIT interpretation results confirmed the depositional settings and rock types of interest in both tight matrix and naturally fractured reservoirs. Understanding the distribution of fractures and karst properties across the conceptual geological regions allowed for calibration of the static and dynamic models. On top of the reservoir model, the implementation of the BIT analysis results helped to constrain key subsurface uncertainties in the principal stresses of the Tengiz 3D mechanical earth model, which is of first order importance for fault reactivation and development of shear zones. The interpretation results allowed determination of the maximum horizontal stress direction from both drilling-induced tensile fractures and borehole breakouts in image-logged intervals. Currently, the imaging tool is included in the standard well logging program of the field, and characterization of the field utilizing these datasets is ongoing.