Cased-Hole Anisotropy Mechanical Properties and Stress Evaluation Using Through-the-Bit Dipole Sonic for Fracturing Optimization in Horizontal Deep Gas Well, North Oman

Abstract

SR gas field is located the North Oman Salt Basin. The BK and MQ are the two main formations targeted for gas production. In most cases, these formations are clastic deep tight gas reservoirs that contain considerable hydrocarbon reserves but exhibit ultralow permeability. The poor connectivity between the pores may significantly reduce the recovery for economic gas production. The formations were initially developed with fractured vertical wells targeting up to 10 different hydrocarbon units. A similar approach was carried forward in highly deviated to horizontal wells targeting the tighter zones. However, the intrinsic geomechanical, petrophysical, and lithological heterogeneities of these tight units impact not only the fracture geometry and conductivity distribution but also the drainage efficiency of the fractured zones. This phenomenon manifests as variations in the units, thereby influencing their contributions to the commingled production, with the areas of higher mobility dominating the total gas production in the current well architectures. A horizontal well designed to obtain the production from the tight zone experienced some challenges on the drilling and completion. To address the operational challenges drilling, logging, and completing horizontal wells in this field, the acquisition of cased-hole logging data to characterize the mechanical anisotropy with a through-the-bit sonic dipole sonic tool deployed via a tractor has emerged as a compelling logging solution. The logging-while-drilling sonic tool has limitations in measuring shear anisotropy, and using the sonic through-the-bit tool in open hole poses for getting stuck. In this case study, sonic data were recorded through casing with the latest-generation slim dipole sonic tool via e-coil across the horizontal section, the first in the world for this type of deployment. The dipole shear sonic tool is capable of recording shear anisotropy, which is used to determine key elastic properties to assess the hydraulic requirements for optimizing the efficiency of fracturing BK units across the horizontal section. We present fundamental considerations for acquiring and evaluating rock mechanical formation anisotropy using through-the-bit dipole shear sonic tool inside tubing by an e-coil. This work uses methods to assess the dynamic variations of in-situ stress by using shear anisotropy and to determine the key elastic properties to identify the hydraulic requirements for fracturing individual units or a combination of them along the horizontal section. Included in the study are considerations of logging requirements, conveyance method, and sonic data processing and results as well as petrophysical evaluation and other reservoir criteria.