Rethinking Well Construction by Use of Drilling With Casing
Authors: Cummins Tracy , Tan Ming Zo , Calloway Greg , Odell Al , Karimi Moji , Rosenberg Steve 
Published: February 2015

Technology Update

Advances in drilling and reaming with casing or liners (DwC, DwL, RwC, and RwL) are yielding unprecedented capabilities in well design and construction. These innovations reflect the continued evolution of a versatile system of technologies that has grown in two decades from a tool to improve efficiency and mitigate drilling hazards to a system enabling advanced wellbore construction.

Advancing the Technology

Modern DwC involves a suite of capabilities for drilling and reaming with either the primary string or liner. The concept has a long history. In the 1950s, the production sections of wells were drilled using tubing that was ultimately cemented in the hole without recovering the bit. Slimhole coring technology from the mining industry was tried in the 1990s in an effort to improve exploration efficiency.

Over the next decade, DwC technology and versatility grew. In addition to eliminating nonproductive time (NPT) tripping drillpipe out of the hole and the associated wellbore problems, DwC emerged as an effective means of proactively mitigating wellbore instability, lost circulation, and pressure transition issues.

The introduction of an integrated casing drive system in the early 2000s enabled the safe and efficient rotation, reciprocation, and circulation of the casing, which led to other benefits such as ensuring high-integrity cementing and zonal isolation. Advances in casing bit design began to resolve the inherent challenge of durability vs. subsequent drillout.

With growing wellbore complexity and challenges, DwC technology evolved from discrete hazard mitigation to a larger capability well plan optimization. Greater capability advanced the end objective from solving an immediate problem to constructing a high-integrity wellbore—as designed and to the total depth (TD). The latest innovations continue this wellbore construction advance on multiple fronts.

Strengthening the Wellbore

Plastering has been one of the more intriguing and elusive benefits of DwC techniques. The so-called smear effect crushes cuttings against the formation to form a barrier to circulation losses and enhance wellbore stability. But achieving it on a regular, predictable basis has been difficult. Plastering occurs in some wells but not in others.

A greater understanding of this process is providing the means to produce and accelerate wellbore plastering reliably, thus substantially strengthening the wellbore. The first field application of the process is planned. Research has shown that the key to plastering is the concurrence of the formation’s permeability and fracture matrix with a wide range of particle sizes in the annulus. If these factors do not correspond, plastering does not occur.

The main variables are the range of particle sizes and the speed of achieving an optimal size distribution. While grinding in the casing wellbore annulus can reduce cuttings to a wide range of size over time, the delay in achieving the appropriate distribution allows time for problems to develop. Early achievement of the optimal particle distribution is critical to success.