Critical path analysis improves rig-moving procedures

LAND RIG DESIGN-1

Dean E. Gaddy
Drilling Editor

Critical Path Diagram [111,998 bytes]
Land Rig Design [161,309 bytes]
Rig 164, on location near Laredo, Tex., for Conoco Inc., is the first of a new breed of mobile, diesel-electric rigs. Its initial mobilization and rig up this past February took 3 days. However, by September, crews were moving the rig in less than 30 hr (Fig. 3). Photo by Preston Hale, courtesy of Helmerich & Payne.[26,069 bytes]
Suitcases have been replaced with an overhanging, cantilevered drag-chain system. This configuration eliminates the time-consuming, difficult work of pulling and feeding electric lines while rigging down and up (Fig. 4).[39,479 bytes]
When it comes time to rig down, the 4-in. vibrator hoses (safety chained) are easily knocked apart and placed on a mud-line trolley. The trolley and electric cable tray, both mounted on rollers, are then retracted completely onto the top of the water tank (Fig. 5 [51,681 bytes]).
A telescoping substructure eliminates the need for cranes and gin trucks to rig down and up. In addition to elevating the substructure, the hydraulic power unit (shown in blue) serves to actuate the raising rams for lowering the mast off the rig floor (shown) (Fig. 6 [44,455 bytes]). Photo by Jim Schlieper, courtesy of Helmerich & Payne.
In order to lower the substructure, these clamps must be removed before telescoping procedures can begin (Fig. 7 [40,828 bytes]). Photo by Jim Schlieper, courtesy of Helmerich & Payne.
An hydraulically raised parallelogram serves to lower and raise the doghouse, eliminating the need for oil field trucks and a forklift. The doghouse can be lowered or raised in less than 5 min (Fig. 8 [36,940 bytes]).
The gas buster (shown in red), choke manifold, and trip tank are skid-mounted and move as one piece. Two hydraulic cylinders and a trunnion arrangement lower the gas buster from a vertical to horizontal position (Fig. 9 [24,503 bytes]).

New concepts in land-rig design have led to substantial improvements in operational performance, safety, and employee productivity for a major U.S. drilling contractor.

The interaction between engineers and field personnel, aided by process-analysis tools, has resulted in the redesign, relocation, and replacement of several key rig components across a series of new builds, helping to reduce rig-moving time, increase penetration rates, and eliminate or mitigate noncritical drilling activities.

Over the last 14 months, Helmerich & Payne International Drilling Co. (H&P) has built 13 new onshore rigs specially designed to alleviate or do away with repetitive and labor-intensive work normally associated with onshore drilling operations.

George Dotson, president of H&P, said the company enjoys a higher utilization rate than the industry average because it commits resources to building new rigs, rather than refurbishing or purchasing outdated rigs. "This allows us to embed new drilling technologies into the design and lay out the rig according to our own specifications," said John Baer, division engineer and project manager for H&P.

More importantly, Alan Orr, vice-president and chief engineer for H&P says, the rigs' new functionality allows employees to concentrate on drilling activities instead of "non-value adding labor."

The company's philosophy of "value by design" is not new. Since 1986, H&P has built or upgraded (capital expenditures greater than $5 million/rig) 71 rigs while retiring 44 obsolete rigs.

H&P's commitment to state-of-the-art technology and its customers' needs are apparent. Twenty-six land rigs contain top drives while another 14 rigs are rigged up to accept this technology.

In order to quickly respond to customer needs, the company keeps a large inventory of draw works, rotary tables, and swivels on hand. In its Houston warehouse, more than 40 new 1,600-hp triplex pumps have been set aside for future building and upgrading activities.

"We use a 'just-in-case' instead of a 'just-in-time' strategy," said Dotson.

In mid-October, 57 rigs were actively drilling out of a fleet of 75 available land rigs. Thirty four of the available rigs are in the U.S., 21 in Venezuela, 10 in Colombia, 1 in Peru, 5 in Bolivia and Argentina, and 4 in Ecuador. Current new-build activity includes 3 rigs earmarked for the U.S., and 2 for Bolivia and Argentina, bringing the total H & P land-rig count to 80.

This first part of a two-part series describes the design features and work flows that have led to a reduction in the rig-up, move, and rig-down cycle. The second part provides details concerning some of the advanced technologies and procedures used to speed up drilling activities and reduce or eliminate nondrilling tasks for a major operator in South Texas.

The critical path

Since 1985, H&P has increased its project-management staff of drilling engineers from 3 to 18. Dedicated to rig design, construction projects, and improvements in well-cycle time, this core group uses project-management techniques such as work breakdown structures, Gantt charts, and critical-path analysis to improve the workflow process (Fig. 1).

The critical-path technique, a project-management tool, refers to those essential tasks that must be accomplished in order, with no slack time in-between, to accomplish the objective at hand within the shortest time-frame possible.1 No project or process can be completed any sooner than what is allowed by the sequential completion of these primary tasks along the critical path.

According to Shane Marchand, project manager at one of H&P's two rig-building yards in Houston, "The use of critical-path project management is essential for our work. Currently, we have four projects under way, using one master schedule to manage our people, equipment, and suppliers. Without it, there would be a logistical nightmare."

Recently, Marchand supervised the construction of four new state-of-the art rigs equipped with Varco 650-ton top drives, 3,000-hp draw works, and all the facilities for a 100-man rig camp.

"It is the noncritical and nonvalue adding tasks such as cleaning the pits while drilling, or having to pull cable and load suitcases in order to pull the draw works, that lengthens the critical path and ties up the drilling process. It is these activities that we seek to reorganize or eliminate in order to reduce cycle time," Baer said.

H&P engineers use critical path analysis for the following activities:

Rig down, move, and rig up more efficiently
Eliminate or mitigate nondrilling, nonvalue-adding activities (i.e., repair work, rig cleaning)
New-build and upgrade construction projects
Reduce flat time (i.e., casing and nipple-up/down activities).

Reducing cycle time

To reduce the cycle time it takes to rig-down, move, and rig-up, H&P engineers analyzed drilling-rig components and subsequent interaction with human resources, moving equipment, and rig components.

These conceptual designs were incorporated into IRI International Corp.'s 1500 class of rigs, four of which are working in South Texas.

According to Baer, "The critical path (denoted in red, Fig. 1) centers on getting to the substructure and derrick as quick as possible. Rigging these two pieces up, first thing, are the critical activities in initiating drilling operations on the next location."

However, unit designs for many rigs across the U.S. and Canada are typically set up so that gin trucks, cranes, and oil field trucks are unable to get to the derrick and substructure until last, producing slack time within the critical path. This is mainly because the SCR (silicon control rectifier) house, engine room, mud pumps, suitcases, and draw works must be moved first (Old design, Fig. 2).

"We went through many design iterations before we finally came up with the current layout for Rig 164 (New design, Fig. 2)," Baer said. Rig 164, currently on location about 40 miles east of Laredo (Fig. 3), is the first of four next-generation, highly mobile, diesel-electric land rigs currently working in South Texas.

"Eighty design changes have been incorporated into the 1500 series of rigs," said John Lindsay, vice-president of U.S. land operations, showing the company's commitment to continuous improvement.

Many of these changes came from field personnel, including the development of a more-ergonomic tong for easier handling and advice concerning the redesign of the location. "It's really been a group effort," Baer said, "and has involved roughnecks, drillers, toolpushers, swampers, drivers, and IRI engineers."

By far, the most important changes involved rearranging the layout of the rig components on location. "What we decided to do was move the SCR house, engines, water tank, and fuel tank [backyard] from the driller's side of the rig to the mud-pit side," Baer said.

In this way, when it comes time to move, the moving equipment has unobstructed access to the draw works, after which the derrick and substructure can be quickly moved to the next location.

Reduced labor

Rig-down and rig-up procedures involve a series of labor-intensive steps that must be accomplished before moving or drilling operations can begin (Fig. 1). Prior to the 1500 series of rigs, the rig-down procedures included the following eight steps:

However, the design features incorporated into the 1500 series of rigs have eliminated or reduced many of the time-consuming activities associated with rigging down the backyard, mud pumps, draw works, and doghouse (Steps 2, 3, 5, and 8), removing many nonvalue adding procedures from the critical path.

Cantilevered cable tray

For example, H&P replaced the suitcases, formerly used to store electric cables along the ground, with a cantilevered cable-tray assembly mounted on top of the water tank (Fig. 4).

When it comes time to rig down, the roughnecks simply disconnect and tie up the electric-cable leads from the SCR house on one end and the leads to the mud pumps, ancillary devices, and rotary table on the other end.

Next, either by hand or through the use of a forklift, the roughnecks swivel the hanging portion of the overhead cable tray towards the water tank. Once this is done, the entire overhead cable assembly, mounted on rollers, is retracted onto the top of the water tank, using a cantilever drag-chain assembly. This innovation allows both the electric cables and water tank to be moved together as one piece.

With the old suitcase design, more than 25, 0.75-in. OD cables, some stretching 150 ft across the location, had to be marked, disconnected, pulled by hand, and folded up in preparation for moving. "This work alone could take half a day," said Jim Schlieper, rig superintendent for Rigs 164, 165, and 154.

Mud-line trolley

The water tank plays another central role by routing the two triplex pumps to the standpipe.

"The key was getting the vibrator hoses and discharge lines off the ground, eliminating tripping hazards, and reducing the work involved with carrying hard pipe. Safety was the issue here, not the routing," Baer said, "although this was an added benefit."

Instead of man-handling vibrator hoses and long sections of hard pipe, H&P eliminated this work by routing hard pipe across the water tank, positioned within a sliding mud-line trolley (Fig. 5).

"To rig down the pumps, all we need to do is knock a short vibrator hose loose and place the hanging end onto the mud line trolley," Schlieper said. This trolley, like the overhead cable tray, retracts along the water tank for transportation.

Piping on the suction side and relief side have also been modified to eliminate or reduce interconnects to the charging pump, relieve-valve discharge lines, and 2-in. pressure bleed lines.

To further expedite mud pump and suction tank mobilization, both components, mounted on a skid, move in one piece. In addition, the primary mud-tank system is skid-mounted as is the draw works.

Telescoping equipment

H&P also chose to use a vertically telescoping substructure (Fig. 6) in place of the conventional box-type structure, eliminating the need for gin trucks and cranes normally used to pull pins and split the substructure box halves.

When it comes time to lower the 22-ft IRI substructure, 8-in. ID clamps, located about 5 ft above the ground, are removed from the four legs (Fig. 7). Next, the hydraulic power unit actuates pistons within the legs, lowering the drill floor down to near ground level. The substructure is then split in half and loaded onto trucks.

Previous methods employed to rig up and down the doghouse, from a height of 22 ft, required the use of two or three oil field trucks, a fork lift, swampers, drivers, and a drilling crew. This process was time-consuming, resource-intensive, and exposed personnel to many potential safety risks.

To reduce the critical-path time for this procedure and improve safety, engineers designed and constructed an hydraulically raised parallelogram, operating by an hydraulic pulley system (Fig. 8). According to Lindsay, when it comes time to elevate the doghouse, it now only takes 5 min to raise it up to the height of the drill floor, using one person.

The IRI mast is also constructed as a trailer package that includes a traveling block cradle to allow moving the traveling equipment while strung up. After the mast has been spotted and pinned to the rig base, the mast is raised hydraulically.

Hydraulic rams and power-adjustment jacks align the mast in a quick and effective manner.

This combination of features allows concurrent rigging up of the power package and mud system. Spotting of all equipment is simplified with the use of v-block alignment guides. According to Lindsay, "All rig up and rig down operations are designed to be accomplished without the use of cranes, and trucking has been reduced to a minimum."

Well-control equipment

The trip tank, choke manifold, and gas buster, important components for well control, are also skid-mounted as one piece (Fig. 10). This reduces the number of individual pieces handled during rig moves and simplifies piping interconnections.

"The 15-ft tall gas buster used to require an acrobat to rig down and up," Schlieper said. However, two hydraulic cylinders and a trunnion arrangement allow the gas buster to lower from a vertical to a horizontal position without any direct physical assistance, enhancing safety for personnel.

Results

There are a lot of activities that must be analyzed to decrease the time it takes to move a rig. "Whenever there is a problem, 85% of the time it will be the system, 15% of the time it will be the worker."2 Nowhere is this more apparent than in a rig-moving operation.

However, H&P has successfully modified the drilling rig, allowing its workers to perform their work in a faster and safer manner. According to Ed Nordquist, Lobo drilling manager for Conoco Inc., "A good rig move in South Texas takes 38 to 48 hr; however, H&P's Rig 164 made it in 29.5 hr, from rig release to spud (Table 1 [142,043 bytes])."

The company has accomplished this by focusing on cycle times, critical paths, and the interrelationship between man and machine.

References

2. Tribus, M., Quality First: The Germ Theory of Management (4th ed.), Alexandria, Va., National Institute for Engineering Management & Systems, 1992.