Hole enlargement while drilling (HEWD) is now widely used in deepwater applications. It provides reduced-clearance casing programs, improves drilling in swelling formations, and helps equivalent circulating density (ECD) management. HEWD applications commonly use an underreamer in a BHA with a rotary steerable system (RSS). Currently, traditional reamer placement results in a long portion of unenlarged hole—rathole—which requires an extra trip to enlarge. A new BHA design is being sought to eliminate the second trip requirement—the objective is to find a feasible solution. Placing the reamer closer to the bit would forgo the need for a second trip; however, the placement of a traditional reamer is limited by its design. In response to such limitation, a solution is proposed to design a rathole elimination (RHE) BHA which includes a lower reamer placed between MWD/LWD tools and the RSS. During HEWD, the lower reamer is in passive (off) mode while a traditional reamer is active. Upon reaching TD, the BHA is tripped back to position the lower reamer above the rathole and is then activated to enlarge the rathole. This RHE BHA design thereby eliminates the second trip requirement. This paper discusses the operational learnings and drilling performance of the proposed RHE BHA design. A field test in Texas is presented and documents the downhole dynamic performance of the single-trip BHA. Drilling dynamics measurement modules (DDMM) were positioned near the reamers to measure the downhole drilling dynamics. This run captured data for traditional HEWD operations and rathole elimination operations. To ensure stable drilling operations, a time-based dynamic simulation perfomed a prerun parametric sensitivity study to help identify the optimal parameters that could deliver high ROP, low vibration, and low stick-slip. A roadmap was made for operational guidelines based on simulation analysis. The test was successfully completed with stable HEWD and RHE operations observed. After completion of the run analysis of the DDMMs, measured downhole dynamic data showed stable downhole drilling dynamics during both HEWD and RHE operations. The RHE operation generated similar levels of vibration and stick-slip at the reamer and MWD/LWD tools compared with the HEWD operation. This field test shows that a single-BHA design can deliver stable drilling dynamics in both HEWD and RHE operations, and demonstrates the capability of the solution in eliminating the second trip requirement. This single-trip RHE BHA design will not only reduce operational costs, but will also lower HSE risk by enabling less BHA handling on the rig floor.
A well plan is essentially a decision-making roadmap for choosing equipment required for drilling the required wellbore. The operator's ability to properly assess offset drilling data and key lithology factors to match available BHA tools and procedures plays a large role in determining project success. Accordingly, the software support systems utilized to interpret and extrapolate data have a direct impact on the ability of drilling engineers to optimize operations. Historically, most well plans were assembled using data from offset wells and prior experience. However in most cases, a rudimentary analysis could not produce a comprehensive picture of the complex, interdisciplinary downhole dynamics that affect drilling performance, especially in the case of limited or missing offset data. Even when reliable data was available, a one-dimensional analysis has failed to completely exploit the available informational value from offset wells. This has forced engineers to be more conservative when designing wells and include more contingencies. The result is operators are drilling in a reactive manner, which often led to decisions resulting in performance degradation rather than optimization. To solve the problem and improve drilling performance in areas of limited/inaccurate offset data, engineers have developed a Mechanical Efficiency Ratio optimization system (MER) that accurately measures the BHA's use of available energy. The modeling tool was tested in several applications and accurately predicted performance including ROP, footage capabilities and dull bit condition. The tool used data and evaluation of rig capabilities, bit/BHA performance, downhole behavior and formation challenges including high-rock strength and interbedded lithologies. The authors will present three case studies that outline how the software program was used to measure system efficiency to determine which bit would have the highest ROP, total footage capabilities and best dull grade estimate compared to offset runs. The MER will also determine if the system (bit/BHA) or the optimized drilling parameters will improve drilling efficiency.
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