Optimizing Wellbore Cleaning Operations in High Horizontal Depth (HD) -To-Total Vertical Depth (TVD) Ratio Wells: Insights from Case Studies in Challenging Well Profiles
Authors: Olawale Olabintan. O , Akram Ahmed , Ismael Yaseen , Yami Ali Al 
Published: February 2024

As the Horizontal Depth (HD) -to-Total Vertical Depth (TVD) ratio increases, the more difficult it becomes to perform the wellbore clean out operations, and the complexity also increases. Challenges such as sedimented drill cuttings and the consequential formation of firm drill cutting beds prevent its effective removal. Even optimized drilling fluid conditioning with optimized processes and highest allowable flow rates, coupled with reciprocal and rotational pipe movements which often lead to severe lost times, including potential lost in hole of strings. Therefore, more planning is required to Optimize Wellbore Cleaning Operations and mitigate potential problems.

In this paper, we detail our best practices to ensure efficient wellbore client based on the field results from the well with high MD-TVD-ration. In the planning phase, these involve the thorough evaluation of the well profile, selection and visual inspection of the wellbore cleanout tools, and anticipated debris accumulation patterns using the Torque and Drag analysis. Additional considerations include the Hydraulic simulation modeling of the fluid and determining the fluid properties, pump rates, and fluid volumes required for effective cleanout in each wellbore geometry and flow paths. For the operational phase, they involve several safety and quality-control, some of which have not been implemented previously.

The solution constitutes to incorporate Circulating subs in the wellbore Cleanout BHA to boost the annular velocity for the more effective wellbore. To take advantage of its unique characteristic for wellbore cleanup operations, a circulation sub is often placed at the depth where the wellbore geometry changes, such as the previous casing shoe. By increasing the pump rate, the hole section below the circulation sub with a smaller annular clearance can maintain the required fluid velocity from the downward split flow.

Operational procedures were maintained for planned operations and contingencies. These procedures were reviewed at a Pre Job-Safety Meeting held a short time prior to commencement of the operations with the involved parties. However, minor revisions were made to the draft procedure from the office to reflect the real data from the Rig. The operational procedure employed for the deployment is to RIH with the bit, wellbore Clean out tools and circulation sub, cleaned the wellbore, pickled casing ID by pumping 75bbl fluid loss control additive spacer (pH 11), followed by 54 bbl solvent/surfactant spacer, and another 75 bbl fluid loss control additive spacer (pH 11). That was followed by filtered water at a controlled pumping rate of 9 BPM and 60 RPM rotating speed. Continuous circulation with the filtered water at a maximum rate until desired fluid cleanliness are met (NTU &lt; 50 and TSS &lt; 0.05%), the well then displaced to completion fluid and drill pipes and BHA pulled out of the hole.

The most significant challenges during the deployment operation are the failure of the circulation Sub due to loosen the guide pin while drilling. However, this was mitigated by modifying the buildup procedure so that the guide pin was torqued before sending the tool to the rig. In addition, selection of efficient cleaning systems is important, along with a detailed displacement procedure to achieve optimum results. Finally, we recommend that utilization of circulating subs for more effective wellbore cleanup will lowering the pump pressure and helps in transporting debris to the surface. Also, utilizing debris recovery tool and magnet just above the Circulation to catch the junk debris circulated up in the annulus.

The results showed that incorporating Circulating subs in the wellbore Cleanout BHA significantly improve the wellbore cleanout. Overall wellbore displacement can be seen with the drop in ECD with the inclusion of circulating sub, despite the pump rate increasing by almost 65% compared to when there is no Circulating sub. There is a higher percentage of flow exiting the string through the circulating sub nozzles, as opposed to the bit. However, the benefits become more pronounced at higher flow rates from several field operations not covered in this paper and shows that the inclusion of a circulating sub makes a dramatic impact. The result of this approach compliments an optimized solution for a comprehensive wellbore cleaning approach and is transferable to other wellbore cleaning operations with high Horizontal Depth (HD) -to-Total Vertical Depth (TVD) ratio to avoid BHA lost-in-hole and significantly reduce non-productive time (NPT).