DRILLING TECHNOLOGY: PART II: Positive and negative events in drilling of Poseidon 29,750-ft well

In the past, oil and gas producers in the US Gulf of Mexico drilled most of the shallow deposits on the continental shelf and now are setting their sites for the deepwater potential. Only recently, however, have seismologists and geologists been able to model deep sedimentary zones in shallow or deep water, especially those beneath salt bodies.

Few wells in the US Gulf of Mexico have surpassed the 20,000 ft. marker, but Chevron USA has been focusing recent search efforts in deeper sediments and in deepwater. Recently, this deep sediment effort focused on a Poseidon Prospect well, located in Mississippi Canyon 727 (No. 1 well). The well was drilled to 29,750 ft (with a TVD or true vertical depth of 29,680 ft).

The semisubmersible Transocean Marianas drilled the well in a water depth of 4,800 ft. Such a deep well requires the right equipment and procedures, but also the right people to complete such a difficult undertaking.

Objectives, accomplishments

Some of the achievement and accomplishments resulting from drilling such a deep well include the following:

• No safety or environmental incidents, no incidences of non-compliance (INC) or national pollutant discharge elimination system (NPEDS) citations during the 166 days of operations.
• The planned depth of 28,100 ft was not only reached, but surpassed. The drill bit reached 29,750 ft. Hole conditions would have allowed continued drilling if required.
• The Schlumberger wireline logs were run to total depth (TD) and reservoir pressures taken as required at a depth of 29,518 ft.
• The 28 in. and 22 in. casing strings were set and cemented back to the mudline, isolating a shallow water flow zone encountered at the 6,542 ft level.
• The 17-7/8 in. casing was set 486 ft into the top of the salt.
• The average angle through the salt was less than four degrees.
• The 14 in. casing point was extended to 17,934 ft because of good hole conditions.
• Five of the eight hole sections were drilled in one pass. Much harder formations were encountered in this area of the US Gulf of Mexico, which required more than one bit for each of the final three hole sections.
• None of the seven tested casing shoes required squeezing.

Other events that took place aboard the vessel during the drilling of the well were as follows:

• The semisubmersible Transocean Marianas was used to drill the entire Poseidon well over a period of 166.5 days.
• A 26 in. hole was drilled using a mud motor without under-reaming below the 28-in. casing. The section was drilled at an average rate of 80 fph faster than normal, saving rig time and kill mud.
• A fully integrated shallow flow plan was successfully implemented to control a large shallow flow at 6,542 ft level. In order to minimize the time required to begin kill operations, all members of the crew knew their jobs in the event of shallow water flow. A Chevron shallow hazards team member was at the wellsite reviewing Schlumberger logging-while-drilling (LWD) logs to assist with predicting hazard zones. In drilling the well, the hazardous zone was picked within 40 ft, and the well had an extremely strong shallow water flow. The flow plan was implemented within minutes of identifying the flow, and the well was killed. Drilling opertions continued within one hour of detection.
• To deal with shallow water flow, 21,425 bbl of mud were sent to the rig. Of this volume, 16,040 bbl were used. This volume yielded 35,000 bbl of (4.0 to 11.9) ppg pad and kill mud. The per-bbl cost was $30, with a total cost of $481,200.
• A specially designed 20-3/4-in. polychrystalline diamond compact (PDC) bi-center bit was used to clean out the 22-in. casing and drill 500 ft into the top of the salt in one pass, saving 2-3 trips using conventional drilling methods.
• An 18-in. bi-center bit on a performance motor was used to drill a salt section (4,500 ft) in one pass, saving a minimum of seven days' rig time over conventional methods.
• A 16-in. casing string was set in the 18-in. hole at 13,525 ft. The casing was cemented without mud losses and met the required formation integrity test (FIT).
• The first installation of 18 in. and 16 in. Dril-Quip Big-Bore subsea wellhead hanger systems were successfully completed.
• A 5-1/2 in. drillpipe landing string was used to land the 1,100,000 #14-in. casing string. This allowed the string to be installed using standard subsurface wellhead running tools and allowed it to be run in one piece, compared with a conventional liner and a tieback. This saved 10 days of rig time.
• The new Baker In-Line liner hanger was used to hang the heavy 11-7/8 in. liner system.
• The Baker "surge" tool was used to reduce synthetic mud losses when running the 9-5/8 in. liner following the lost circulation event. The estimated savings of 2,200 bbl ($300,000) of mud was realized as a result of this technology.
• The Minerals Management Service (MMS) permitted Chevron to plug and abandon the well with all casing in place, saving $500,000 of rig time.
• Deep wireline logging operations, using Schlumberger's Capstan and Super High Strength cable (15,500 lb allowable pull) were successful.
• The casing racks on the workboats, providing for tubular transportation to and from the Marianas, saved time and money.

Operations aboard the Marianas that went well during the drilling operations included the following:

• Jetting in the 36 in. casing within required angle tolerances was accomplished while setting anchors.
• Mobilization of a large quantity of mud, casing, drillpipe, and drilling riser during the early stages of the well was successful.
• The use of a mud mixing manifold for building kill mud and pad mud from 16 ppg heavy mud was very effective.
• A detailed planned cement job combined with sound cementing practices and equipment was successfully implemented. The separate string cementing costs were 28 in. SWF job - N2 - $312,000; 22 in. SWF Job - N2 - $375,000; 17-7/8 in. - $160,000; 16 in. - $240,000; 14 in. - $244,000; 11-7/8 in. - $161,000; 9-5/8 in. - $134,500; and the P&A plugs totaled $233,600. The total cost for cementing was $1,860,100.
• Success circulating out three kicks from depths of 15,125 ft, 18,010 ft, and 26,954 ft without stuck pipe or loss circulation problems were achieved through teamwork.
• The installation of a 4th mud pump assisted with hole cleaning during large hole drilling operations.
• The inspection program for the drillpipe, the BHA components, and the liner hangers were made in a timely fashion. They included: drillpipe - 1,696 jts/52,576 ft - $122,950 - 382 joints rejected; BHA connections - 2,031; BHA parts and casing tools - 1,895 parts; BHA and casing tool defects - 139; BHA and casing tool cost - $134,241; TH Hill monitoring costs - $120,607; total monitoring and inspection costs - $377,798.
• Operations performance by workboats handling drill pipe went well.

Challenges

Among the events that did not go well during the 166.5 day operation are the following:

• A hurricane threat did not allow 28 in. and 22 in. casing to be pre-run in the moonpool.
• The hydraulic tongs were so large that they became more of a safety hazard during the make up of the 28 in. and 22 in. casing than the bull tong they eliminated.
• The low variable deckload capacity of the Marianas resulted in inefficiency in the running of large casing strings and handling large volumes of heavy drilling fluid.
• A greater hydraulics capability was needed than the Marianas could supply in order to efficiently drill the salt section at high penetration rates and low angle.
• The drilling of the 14-3/4 in. bi-center hole for the 11-7/8 in. casing was slow due to the encounter with hard formations.
• Measurement-while-drilling transmission of data failed in the drilling of the 8-1/2 in. hole section.