Wellbore Assessment Using Time-Lapse LWD Calipers

Abstract

Abstract Logging While Drilling (LWD) calipers (ultrasonic, density, and resistivity) have been available for several years, but their use is still limited due to the belief that they are not as reliable as the mechanical calipers obtained from wireline (WL) logs. One possible reason for this belief is the different time at which the LWD and WL measurements are made. In fact, LWD density derived calipers have their advantages over the WL calipers. One example is that they cover relatively larger portion of wellbore circumference, thereby providing a better characterization of borehole shape. A 3D caliper image can be obtained using 16 radii density measurements around the wellbore. Another advantage is that these measurements are available in real-time and borehole deterioration with time can be measured with time lapse acquisition. Accurate logging-while-drilling (LWD) borehole caliper data is important for drilling, logging and well completion. An accurate LWD caliper can greatly minimize risk and improve quality by bringing critical new information to these applications. During drilling, caliper data can be used to monitor the wellbore condition, providing early warning of borehole washout and impending wellbore instability, thus allowing the driller to take remedial action. During well completion, the caliper data can be used to accurately evaluate the volume of cement required to fill the casing annulus as well as aiding in the section of casing points or packer intervals by identifying in-gauge hole intervals. During logging, a reliable caliper is essential to correct some formation evaluation measurements for borehole size and to evaluate the quality of almost all LWD logs. A caliper can be used to plan services (such as formation testers) that may be affected by unfavorable borehole conditions. In this paper, the main objective is to characterize the change in wellbore shape with time and relate it to formation characteristics and drilling and completion operations. Any relationship observed and correlated will be utilized to optimize these processes. The results presented in this paper show that the borehole degradation increases with time and that the accuracy of LWD derived caliper is 0.1in when both the LWD caliper and WL caliper runs are done at similar time periods. The depth of investigation in this case study is 2.25in.