• Sequencing pad development improves stacked reservoir recovery.
  • It is possible to both increase well density and improve individual well recovery.

You’ve heard of cube development. You’ve heard of pattern development. Now add tank development to the lexicon of terms describing full field development.

To be sure, the industry is early in the strategic evolution to completing multiple wells on a single pad, which characterizes more than 90% of wells in the Bakken and Marcellus. Other regions, such as the Midcontinent, are earlier yet in evolution along an arc of tight formation exploitation that moves from discovery to delineation, optimization and full field development.

A major issue in the traditional strategy of capturing acreage first and developing acreage later stems from drilling a parent well to retain acreage via production followed by a return to build out the lease with multiple child wells. That strategy exposes the industry to production issues associated with parent/child well interference.

The parent well creates a pressure sink. Infill wells, added later, impact production in the parent well, often negatively, but also generate diminishing returns as energy applied to hydraulically fracture infill wells migrates toward the parent well’s pressure sink. Suboptimal recovery and diminishing returns impact capital efficiency in operations and curtail access to full financial leverage in reserve-based lending.

E&P companies use strategies to subvert this phenomenon such as repressuring and shutting in the parent well before fracture stimulating a neighboring infill well. Some larger E&P companies use a factory approach by drilling dozens of wells in a section then completing those wells simultaneously.

Branding for those techniques include terms such as “cube” or “pattern” development, and entail significant upfront capital costs for drilling, completion and infrastructure development, while creating logistical challenges involving sand and water sourcing, treatment and disposal, long before generating revenue when wells are turned in-line six to nine months later.

Engineers from QEP Resources Inc. proposed a solution to these challenges by recapping field experiments in two stacked pay Spraberry drilling units in the Midland Basin at the 2018 Unconventional Resources Technology Conference summer gathering in Houston.

QEP engineers labeled the practice as “tank” development. It involves drilling, completing and turning wells in-line simultaneously for each well pad. However, think of it as a multiphase sequence that involves a drilling unit such as a four-well pad, a temporary nonactive neighboring pad as a buffer, the completion sequence, which creates a pressure wall, and the final sequence, which turns all wells into line.

Specifically, it involves drilling all wells in the initial drilling unit before the rig moves to the next pad. As the rig moves to a third pad, stimulation crews employ a top down completion sequence on the first pad, then move to the neighboring pad. As the crew reaches the third pad, wells in the first pad are brought online only after a pressure wall separates wells in completion on the third pad from wells being turned in-line on the first pad. The sequence of events is repeated along neighboring pads as rigs, stimulation crews and production transit across the reservoir.

QEP’s stacked play Spraberry experiment showed the methodology eliminates parent/child well interaction and increases stimulated rock volume by adding pressure to the reservoir faster than it dissipates. The additional pressure creates a more complex fracture network.

Greater yield comes from tighter well density— up to 16 wells per mile versus 10 previously—and improved recovery for each drilling unit, which amplifies asset value. In other words, the method harvests more hydrocarbons from individual wells and more hydrocarbons in aggregate from all wells in a drilling unit. Tank development also lowers well costs by reducing surface complexity.

Stay tuned.