Abstract
Abstract
Petrophysical analysis of well logs evaluates the lithology, porosity, water saturation and net pay zone where resistivity logs are used to indicate the fluid type within the depth of investigation of the measurements. The introduction of multi-axial electromagnetic (EM) resistivity measurement enabled resolving vertical and horizontal components for advanced petrophysical analysis. This paper discusses the introduction of a new logging while drilling (LWD) digitally compensated closer to the bit multi-axial EM resistivity tool enabling improved petrophysical analysis, better coverage of the drilled open hole leading to faster real-time well-placement decisions and increased well productivity.
In highly deviated and horizontal sections, LWD is generally considered the most viable option for well logging. However, LWD sensors in traditional bottom-hole assemblies (BHAs) are usually placed at a minimum distance of about 35 ft from the bit due to the presence of a steerable drilling system between the bit and the logging tools which leads to relatively late petrophysical analysis of the drilled interval which can result in sub-optimal well placement. The introduction of an advanced near-bit, digitally compensated, multi-axial electromagnetic resistivity measurement located within the downhole steering system has proven to add value beyond addressing this challenge.
Closer to the bit resistivity measurement enabled data availability as soon as new footage is drilled which facilitates faster real-time, interactive well-placement decisions to optimize steering the well within the target zone leading to increasing productivity while minimizing hole tortuosity. The new configuration added value by resolving effects from nearby boundaries which can be utilized in petrophysical evaluation as well as projecting geo-mapping "At-the-bit" providing lithology indicator and fluid distribution through resolving vertical and horizontal resistivity components.
This paper presents the outcome of deploying the industry's first close-to-the-bit LWD compensated resistivity sensor, embedded in the rotary steerable drilling system demonstrating the evaluation of almost the whole interval of the well drilled, enhanced petrophysical analysis benefiting from resistivity measurements with minimal formation exposure time, timely preparation of the completion design by making real-time decisions on completion and isolation resulting in saving costly rig time.