Schlumberger

Case Study: IDEAS Designed PDC Bit Exceeds Target ROP, Saves Operator USD 30,000 per Well

New field benchmark set, offshore Indonesia

Challenge: Drill 9 1/2-in section shoe-to-shoe with the highest possible ROP while minimizing shock and vibrations.

Solution: Use IDEAS integrated drillbit design platform to optimize a standard SHARC high-abrasion resistant PDC drill bit, to provide an application specific bit design.

Result: After drilling 17 wells in the offshore field, the SHARC MSi616 delivered shoe-to-shoe performance while exceeding the target ROP by 17% and saving USD 30,000 per well.

Durable PDC bit with high ROP potential required

Total Exploration and Production (TEPI) had to drill a deviated wellbore through a thick shale/sand sequence to develop gas reserves trapped in Miocene age sand bars deposited, offshore Indonesia. Historically, the 2,100 m to 2,400 m tangent sections were drilled with a 9-in PDC bit on a rotary steerable system (RSS). The lithology is mainly soft shale and abrasive sandstone, but sections also contain intermittent coal/limestone stringers and become increasingly interbedded with depth. The well plan calls for a 45° tangent section followed by sequential angle drop to 10° increasing verticality for the subsequent 6-in production hole run. In the past, Smith Bits’ 9 7/8-in PDCs run in the field suffered from unstable drilling, which resulted in performance degradation. The unwanted drillstring harmonics reduced overall ROP to an unacceptable level and caused vibration induced impact damage in the harder formations. Field analysis revealed the 2 to 3 level dull cutter condition in the shoulder area resulted equally from abrasive wear and chipping/breakage. To cut costs, the operator reduced the hole section size to 9 1/2-in, but with the same objectives: drill shoe-to-shoe in one run at the highest possible ROP with minimal shock and vibration. To remain competitive in the application, Smith Bits would need to design a new-style PDC bit that could consistently drill from under the 10 3/4-in casing shoe to section TD, in one run, at a target ROP of 55 m/h or better, with minimal vibration.

Cutting structure analysis

The optimization effort would be more complicated than normal because the hole size reduction occurred before engineers could benchmark 9 7/8-in bit performance and capture critical field information. The lack of measurable target data would hamper the effort to improve existing 9 1/2-in bit performance because specific regions of the field are more difficult to drill than others.

A team of Smith Bits field engineers and bit designers gathered and analyzed all relevant drilling data and concluded the existing 9 7/8-in six-bladed matrix body bit with 16-mm cutters was the best base design and would serve as the starting point. The limited data set could prove problematic and force a trial and error approach to improve bit performance. To avoid costly and time-consuming field trials, designers used the IDEAS drillbit design platform to investigate downsizing the PDC bit and optimizing its cutting structure. i-DRILL drilling system design simulations were run to model bit and BHA behavior through a wide range of drilling parameters and the various lithologies encountered. Iterative design changes were made to the bit’s cutting structure to ensure stable drilling and high ROP potential. The advanced modeling tool was used in combination with DBOS drillbit optimization system, which pinpointed the unconfined compressive strength (UCS) of the shale at 3,000 psi with the sandstone fluctuating between 9,000 psi and 15,000 psi. The UCS study enabled technicians to select an in-house library rock sample that matched the field formation to replicate the fundamental shearing action in the laboratory.

Hydraulic analysis

Achieving the high ROP objective would also require improved bit hydraulics to rapidly evacuate the large amount of sticky drill cuttings that would be generated during drilling the soft shale formation. Engineers ran computational fluid dynamics to study fluid flow and made adjustments to nozzle location and orientation until an optimized anti-balling configuration was found. The combination of modeling and in-depth analysis of field data confirmed that the existing six-bladed matrix body PDC bit equipped with 16-mm ONYX premium cutters had the best chance to deliver shoe-to-shoe performance at the highest possible overall ROP on a PowerDrive rotary steerable system. Based on these findings, a 9 1/2-in SHARC MSi616 PDC bit was identified as the bit candidate to accomplish the operator’s objectives.

IDEAS platform driven results

The new 9 1/2-in SHARC MSi616 PDC bit has been run 17 times in the offshore field and has exceeded all operator expectations by drilling an entire section in one run at a high median ROP of 64.4 m/h. The bit’s best-in-field performance is 17% higher than target ROP, 12% greater than other products, and 51% faster than previous Smith Bits offerings. The bit successfully delivered all directional objectives, and rig personnel reported smooth drilling with minimal stick-slip and no shocks. The MSi616 recently set two new area ROP records, drilling 79.9 m/h on one rig and 80.9 m/h on another rig. Based on typical penetration rates (median ROP), running the new 9 1/2-in MSi616 enabled TEPI to cut approximately four hours off on-bottom drilling time for savings of at least USD 30,000 per well.


Download: IDEAS Designed PDC Bit Exceeds Target ROP, Saves Operator USD 30,000 per Well (0.69 MB PDF)

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Median ROP comparison before design optimization project.Median ROP comparison following design optimization project.
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