Cased Hole Completions System Safety – Part 1

Completion systems are the components necessary to complete a well after it is drilled and prepare it for production. There are a variety of completion options available to oil and gas operators. Cased-hole completion systems, for example, vary from relatively simple single-zone low-pressure/low-temperature (LP/LT) designs to complex high-pressure/high-temperature (HP/HT) applications that are commonly found in deepwater.

Cased-hole completion involves running casing or a liner down through the production zone, and cementing it in place. A good cement job is the primary barrier for effective zonal isolation and is the standard industry method to protect the wellbore from unwanted and dangerous influxes of formation fluids, solids and gases. In deepwater wells, the ability of the cement to reliably contain reservoir pressures is threatened by fluid losses to the formation during cementing operations that is impacted by higher pressures and temperatures, extended laterals and unstable formations.

It is well known that a bad cementing job presents serious safety risks to the drilling rig, rig personnel and the environment and can be very costly and time consuming to fix. Micro-annulus (annulus is any void between any casing and the casing immediately surrounding it) channeling and flow, for example, can occur when there is poor cementing across gas or oil zones.

According to Baker Hughes, this micro-annulus flow not only fails to provide a primary barrier for well control, it can also hinder the operator’s ability to properly abandon the well in an emergency situation. In extreme cases, inferior cement might allow gas or oil to migrate to the surface, leading to a blowout. If this happens with gas, a surface explosion may happen very quickly, if not checked. Ultimately, the completion system employed in deepwater HP/HT wells must be safe and efficient in order to be cost-effective to any operator.

Source: Baker Hughes, Drilling Contractor, IADC