Third-generation rotary steerable drilling system and real-time downhole data monitoring improve efficiency.

The application of advanced drilling technology - new-generation rotary steerable drilling system and real-time downhole data monitoring capability - plus joint well planning and design have combined to improve directional drilling efficiency for the Mad Dog project in deepwater Gulf of Mexico.

Deepwater development

The Mad Dog project is in Green Canyon 782 in the Gulf of Mexico. BP is the designated operator with BHP Billiton and Unocal as partners. The producing sands are located at about 20,000-ft (6,100-m) depth below a salt body 5,000 ft to 8,000 ft (1,525 m to 2,440 m) thick. Directional wells through the salt body are necessary to meet well placement, completion and production objectives.

Well planning and design

Baker Hughes Inteq provided directional drilling, logging while drilling/measurement while drilling (LWD/MWD) mud logging, and real-time data transmission services for the pre-drill program, which consisted of batch setting three wells (MD#5, 6 and 7) and drilling two wells (MD#5 and MD#7) to total depth (TD) and performing openhole sidetracks on two existing wells (MD#4 and MD#2). The scope of the drilling project was expanded to batch set four more wells to 36-in. structural pipe setting depth.
During the planning phase, detailed engineering analysis was performed to design well profiles, implement new drilling tools and optimize bottomhole assembly (BHA) configurations.

Drilling and data acquisition objectives included:

• Optimize well trajectory and BHA to minimize drilling trajectory concerns;
• Drill smooth well bore with minimal dogleg severity;
• Improve rate of penetration (ROP) and overall drilling efficiency in each section;
• Drill each section in one run;
• Optimize ROP in production section to meet all the data acquisition needs;
• Perform openhole sidetracks with rotary steerable tools;
• Provide real-time data for office personnel to monitor the wells and improve decision making.

The third-generation 9-in. AutoTrak rotary closed loop system (RCLS) was used for the first time to drill the 17-in. sections on the MD#5 and MD#7 wells. This was also the first commercial application of the 9-in. Ontrak MWD sensor sub. Rotary steerable drilling tools were then used for all the hole sections as the primary drilling technology. The Advantage software platform provided a single, shared database for all drilling, formation evaluation and mud logging data. Riglink satellite data communications and Total Recall data management provided real-time data.

36-in. by 26-in. batch drilling

The batch setting operations were performed with significant performance improvement between the first phase of three batch sets conducted prior to drilling the wells to TD and last four batch sets performed after the drilling program. The performance improvement in jetting times was accomplished through the use of lessons learned and optimization of the BHA and jetting.

Drilling performance highlights for the MD#5 well are described in the following sections.

17-in. hole section

In the 17-in. hole section, significant improvements in drilling performance were accomplished with the MD#5 well. Real-time data allowed close monitoring and improved decision making during drilling in the tight pore pressure/fracture gradient window. The wells were kicked off in this section and directional work was performed to achieve the well placement objectives and drill 500 ft into salt to set the 13-in. casing.

Performance highlights included:

• Drilled 3,081 ft (939 m) of sand/shale formation followed by 377 ft (114 m) of salt [total 3,458 ft (1,054 m)];
• Performed kick off and build from 0.7° to 22.5° and turn from 18.9° to 146.40°;
• Average DLS was 0.79°/100 ft (30.5 m);
• Drilled 3,458 ft (1,054 m) in 27.5 on-bottom drilling hours compared to 46.9 hours on MD#4 well, resulting in 42% performance improvement.

12-in. by 13-in. hole section

This section required drilling the salt body and performing additional directional work through salt to meet the drilling and geological objectives.

• 8-in. AutoTrak RCLS system was used in conjunction with Hughes Christensen Genesis PDC bit to drill 5,278 ft (1,609 m) of salt and 1,177 ft (358 m) of subsalt.
• Directional profile required drilling a tangent and perform drop in salt.
• Drilled salt at an average ROP of 220 ft to 240 ft/hr (67 m to 73 m/hr), an improvement of 93% on-bottom ROP compared to MD#4.
• Excellent control on drilling dynamics.
• ROP was slowed down to 150 ft/hr (45 m/hr) below salt to look for casing seat.

9-in. hole section

• Drilled 4,452 ft (1,357 m) in 39.6 on-bottom drilling hours at an average ROP of 112 ft/hr vs. 100 planned drilling hours.
• Average DLS: 0.54°/100 ft (30.5 m).
Benefit and value

On the MD#5 well, BP met its "one run per hole section" objective and improved drilling efficiency by drilling the well in 7.8 drilling days, the best performance for Mad Dog wells to date. The directional cost for the well was approximately half of the benchmark MD#4. The team drilled 6,500 ft (1,982 m) through salt in only 2 days compared to the previous Inteq record set at MD#4 for drilling 4,500 ft (1,372 m) of salt in 4 days. No short trips were made on the complete well and all the casing strings were run to TD without any problems.

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