Downhole Drilling Dynamics of Innovative Rathole Elimination BHA in Hole-Enlargement-While-Drilling Operations

Abstract

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.

Wringing effect prevention on a piston design in a downhole drilling tool

“…Intelligent downhole tools often require moving mechanism designs, such as pistons. For example, reamers use moving mechanisms to extend or retrieve cutting blocks [3, 4]; coring has moving pistons to control rock sampling barrels [5], and the packer system incorporates moving valves [1]. The moving parts or pistons rest on a mandrel, or non‐moving parts, in the default position; in downhole, after receiving a real‐time command, the moving parts initiate motion and separate from the static mandrel.…”