Case Study: Record-Breaking Drilling Operation Saves POC More Than USD 30 Million in 23 Wells

POC, Schlumberger, and COSL collaborate to optimize procedures in South China Sea and drill complex 3D wells from spud to completion in record time

Challenge: Drill complex 3D wells to access attic oil in mature field, South China Sea.

Solution: Develop detailed procedure to optimize drilling performance and well placement.


  • Set new field record for drilling time from spud to completion.
  • Saved more than USD 30 million in 23 wells.
  • Saved more than 80 days from ODP design.
  • Exceeded forecast production.

Access attic oil in mature offshore field 

China Oilfield Services Ltd. (COSL), working in conjunction with Schlumberger, contracted with the Panyu Operating Company (POC), a branch of the Chinese National Offshore Oil Corporation (CNOOC), to drill 25 wells from a new platform—PY4-2B—erected in place in Panyu field in the South China Sea. COSL and Schlumberger collaborated in designing and planning the wells, and Schlumberger executed the drilling.

Because the target zones in the mature field were beneath the platform, it was necessary to drill 3D wells with a “pregnant lady” profile and high dogleg severity (DLS) to land them at the proper angle to navigate the reservoir within 0.5 m of its roof to access attic oil while remaining above the oil/ water contact (OWC). Landing the wells was made more difficult by uncertainty about the TVD of the target zones and formation dip at the landing points. Adding to the challenge was the risk of well collision, since the platform slots were spaced just 2.29 m apart and another platform with 38 existing wells was only 900 m away. 

Optimize drilling performance and well placement 

Working together, POC, Schlumberger, and COSL overcame the challenges and achieved POC’s objectives for the Panyu project—increased production and reduced drilling cost. Lessons learned on the first wells were used to develop a detailed procedure for well execution that optimized overall drilling performance and well placement. This procedure included the BHA to be used for each well section. 

The BHAs for the 16-in tophole section and the upper portion of the 12 1/4-in curve section incorporated roller cone bits from Smith Bits, a Schlumberger company, and PowerPak steerable motors. That combination allowed fast sliding for required DLS, provided toolface control to mitigate collision risk, and reduced reactive torque when building up the curve. 

The BHA that finished the curve in the 12 1/4-in section and landed the well used a PowerDrive Xceed ruggedized rotary steerable system (RSS) for directional control with increased ROP. This RSS, which had a stabilization design customized to achieve the required DLS, was teamed with a modified version of the PDC bit normally used with an RSS in Panyu field. Modifications to the bit design, based on lessons learned drilling the first wells, included changes to the blade profile, the number of blades, cutter size and back rake angle, depth of cut, and gauge length with taper. To reduce or avoid bit balling issues, bit hydraulics also were changed. 

The BHA for the 8 1/2-in lateral section also incorporated a PowerDrive Xceed RSS, which was steered using real-time data provided by the PeriScope bed boundary mapping service. PeriScope service allowed the fast response needed to keep the lateral within 0.5 m of the reservoir roof and above the OWC. With a goal of continuously improving the performance, steering, and well placement, PowerDrive Archer high build rate rotary steerable system was introduced to the project. The RSS drilled the 8 1/2-in sections of the final three wells achieving DLS assurance,rapid steering response, and faster ROP. 

Landing of the 12 1/4-in curve section and navigation of the 8½-in lateral section were monitored in real time by a well placement team located in POC’s office. This enabled the team to make timely steering decisions in conjunction with POC. 

Increase production and reduce costs 

Use of the PeriScope boundary mapping service to place the wells’ 8 1/2-in horizontal sections enabled the laterals to be extended beyond their planned lengths to access additional oil. In the first ten wells completed, actual lateral length exceeded planned length an average of 70 m per well, and actual initial production per well exceeded forecast production an average of 1,288 bbl of oil per day, with only 1.1% water cut. 

The detailed procedure developed to optimize drilling performance significantly reduced drilling cost per well. As a result, POC saved an average of USD 750,000 per well—15% of the average AFE budget of USD 5 million per well—on the first 17 wells drilled from the PY4-2B platform. 

The time to drill those wells from spud to completion averaged 17.6 days per well—7.4 days less than the average of 25 days for offset wells. Prior to this campaign, the field record for drilling a well from spud to completion was 16.8 days. That record was broken on the sixth well drilled from PY4-2B, Well B09H, which was drilled from spud to completion in 15.6 days. All the wells drilled from PY4-2B since then have been finished in less than 16.8 days, including the current record holder, Well B18H, which was drilled, from spud to completion, in 14.1 days. 

There have been no lost in hole or stuck pipe incidents in any of the wells drilled from PY4-2B.

Download: Record-Breaking Drilling Operation Saves POC More Than USD 30 Million in 23 Wells (0.12 MB PDF)

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