Distinct Applications of MWD, Weight on Bit, and Torque

Abstract

Summary Recent enhancements to measurement-while-drilling (MWD) tools have increased drilling efficiency in directional wells on the North Slope of Alaska. With information provided by downhole weight on bit (WOB) and torque sensors, more timely and accurate decisions have been made, resulting in lower costs per foot. Specific applications of this technology include bit optimization, directional feedback, and drillstring-friction analysis. This paper discusses actual cases where the use of data from these paper discusses actual cases where the use of data from these downhole sensors has improved drilling performance, This information will benefit those interested in optimizing polycrystalline-diamond-compact (PDC) and rollercone bit runs, polycrystalline-diamond-compact (PDC) and rollercone bit runs, improving directional-drilling assembly predictability and performance, minimizing surface torques, and planning performance, minimizing surface torques, and planning high-departure wells. Introduction Several unique applications have emerged from use of downhole WOB and torque MWD measurements and modeling based on these measurements. The applications have come to light mainly as a result of the consistent use of these measurements in wells on the North Slope. These applications can be divided into two main categories: bit performance and mud-motor/directional-drilling evaluation. The PDC-bit rate of penetration (ROP) was maximized by maintaining the optimum downhole WOB and torque. Another PDC bit was identified rapidly as unsuitable for the formation being drilled, and time was not wasted trying to make the bit drill. Bit trips were avoided by pinpointing which low ROP's were not caused by the bit. Undergauged bits were detected quickly, preventing the drilling of undersized hole. Locked cones were preventing the drilling of undersized hole. Locked cones were diagnosed during drilling, which allowed the bit to be tripped before a cone was left downhole. A fractured mud-motor shaft was detected quickly with downhole torque, which minimized time spent trying to drill. The reliability of directional drilling with a packed-hole assembly has been improved by use of downhole WOB. These examples are discussed in detail in this paper. Background To minimize the effect of drilling and production facilities on the surface, all Arco's fields on Alaska's North Slope have been developed with directional wells with a minimum number of pads. The Prudhoe Bay and Kuparuk fields are onshore and were designed to allow each pad to access bottomhole sites within 4 sq. miles. Consequently, most wells did not have to be drilled with a departure greater than 8,000 ft. However, because much of the Lisburne producing formation is offshore, many bottomhole sites cannot be reached without drilling high-departure (greater than 10,000-ft) wells. To date, six high-departure wells have been drilled in the Lisburne field. The average departure for these wells at total depth (TD) was 11,500 ft, and the highest departure was 12,153 ft. Fig. 1 shows the surface and bottomhole locations of these wells in relationship to the coastline for Lisburne field. Because they have drilled greater than 1,400 directional wells on the North Slope, including the high-departure wells at Lisburne and 40 horizontal wells at Prudhoe Bay, operators and service companies have developed or refined several directional-drilling tools and techniques. These applications have included steerable motors, top-drive systems, aluminum drillpipe, and MWD tools. One area that has become increasingly important is the measurement and use of downhole data. Theory PDC Bit Optimization. Koskie et al.'s procedure for optimizing PDC Bit Optimization. Koskie et al.'s procedure for optimizing the PDC bit requires measuring the forces on the bit and knowing the formation. The MWD's of downhole WOB and torque measure actual forces on the PDC bit. The formation type being drilled is predicted with the dimensionless torque value, TD, the torque per unit weight: per unit weight: (1) During drilling of shale, the optimum downhole weight can be determined by performing a drill-off test. When operating at the optimum downhole weight, the maximum downhole torque can be recorded for future use. By maintaining the downhole weight and torque close to but not exceeding their maximums, ROP can be optimized, hit life can be increased, and bit floundering can be avoided. This involves different drilling procedures for different formations, as summarized in Table 1.