Implementing Eccentric String Reamer With Enhanced Wellbore Strengthening Practices – A Case Study

Abstract

The legacy concession comprises mature fields with a well-known wellbore problem, lost circulation while drilling. Highly depleted reservoirs and pressure ramps at deeper sections are the main contributing factors inducing drilling fluid loss events. This case study describes a technique for lowering equivalent circulating density (ECD) in the Gulf of Thailand (Got), specifically in PTTEP’s legacy operating area, while drilling with a combination of using eccentric string reamers (ESR) and adjustable gage stabilizers (AGS) bottomhole assembly (BHA) and enhanced wellbore strengthening (WBS) practices. Since lower borehole pressure might lessen or postpone drilling fluid loss events, lower ECD in the slimhole is preferred when drilling depleted reservoirs in mature fields. In order to maximize reserves capture and perhaps penetrate otherwise unrealized pay horizons, it may be possible to further progress in deepening well depth by delaying losses. While there were a number of approaches to lower ECD, the majority of these involved costs related to significant modifications to the drillstring and/or casing design specifications, so there was a need for a low-impact, low-cost operational solution. Hole-opening is one of the approaches to increase annular clearance. A one-trip approach that does not significantly affect a holistic way well factory is limited.[SJ1][SH2] Rather than using ESR, other alternatives are evaluated but are not fit for purpose, such as reducing drill pipe size and lowering intermediate casing wall thickness. Additionally, the chosen course of action must not jeopardize the operational dependability of the drilling equipment and be suitable for a high-temperature reservoir drilling environment. ESR is a straightforward but contentious hole-opening tool. ESRs are straightforward because they have cheap running costs and no moving parts or cutting blocks to relocate. The reason they are problematic is that it is uncertain if the drilling dynamics and tool eccentricity will properly open the hole to the target diameter. An eccentric reamer solution was selected for field trial and possible development, as this hole-opening application is confined to annular clearance for fluid, not mechanical clearance. A reamer design with the required enlargement ratio (6⅛-in. to 6⅞-in.) was specifically designed and built along with placement software to help locate the tool optimally in the BHA.