To walk or skid? The question is of growing interest as the oil and gas industry transitions rapidly to pad drilling and batch completions. Pad drilling has grown from less than 20% of horizontal wells in 4Q 2012 to more than 60% of horizontal wells as 2014 gets under way.

Hart Energy surveyed manufacturers of mobility systems to assess market penetration of pad-capable rigs with self-moving packages. Survey results suggested that nearly 40% of the domestic land fleet will have either a walking or skid system by year-end 2014.

Nearly all of the anticipated 80 to 100 newbuild domestic land rigs in 2014 will be equipped with self-mobility packages, with roughly two-thirds of those being walking systems.

Moving rigs to adjacent wellbores in a pad setting is not new. In the early days, bulldozers dragged rigs to adjacent wellbores. Both skidded and walking systems have been available since the 1970s, but the packages were a niche application until the transition to unconventional gas about a decade ago. The initial impetus for pad drilling (and self-moving rigs) originated in the Rockies because of environmental considerations.

In Colorado’s Piceance basin, it was difficult to get permits for additional drilling sites. In Wyoming, seasonal restrictions prevented rig moves because of animal migrations. Pad drilling solved both issues. Later, pad drilling found an outlet in the Barnett shale as a means to drill multiple laterals in an urban setting, while rugged terrain in Appalachia further encouraged the spread of pad drilling.

However, the Eagle Ford proved the breakthrough opportunity. Operators had plenty of surface acreage and began to view pad drilling as the most economical way to gain incremental efficiencies at the well site. Pad drilling – and self-moving rigs – became an end in itself, prompting a step-level change in drilling efficiency in terms of wells per year.

Skidded systems enjoyed an early market edge, based on importing the offshore concept of parallel wells along a rail system. Onshore, skidded systems implemented in the Piceance basin allowed operators to conduct simultaneous operations on the same well site.

Walking systems have gained momentum lately since they fit the nature of the unconventional drilling cycle. Operators drill a single well to capture acreage, then return later to the well site to add more wells. Walking systems allow a rig to move about over existing wellhead equipment.

Manufacturers contacted in the Hart survey noted skidding packages enjoyed an initial advantage because the systems were less expensive to install as the industry began to ramp on pad drilling. Respondents pegged the average cost of a skidded system at slightly more than US $700,000 vs. slightly less than $1 million for walking systems. Skidded systems are marketed as a means for better weight distribution, are less costly to install and operate, and are faster to retrofit – eight weeks on average vs. 11 weeks for walking systems. However, walking systems feature flexibility and better automation, are self-leveling, and require less trucking between well sites.

The primary manufacturing effort over the last two years involved retrofitting existing rigs. Manufacturers told Hart that the current retrofit market is evenly divided with 75 systems each on order books with interest in skidded systems more prevalent on rigs headed overseas.

Currently, about 30% of the 1,700 domestic land rigs are outfitted with self-moving packages, split roughly 55% to 45% in favor of walking systems, but manufacturers indicated walking systems will become the future standard.

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