Extreme HPHT wells – Tackling 20,000 psi

Well Control specialists face serious challenges when dealing with extreme HPHT wells, where pressures may exceed 20,000 psi. According to well control specialists, challenges associated with extreme HPHT operations may include:

Narrow safe operating “windows”, where drilling personnel must remain adequately informed and aware of downhole conditions to ensure early kick detection and response.In this case the wider the safe operating window is the easier it is to assure well control safety.

High wellbore temperatures, where normally very high-pressure formations are also typically very hot formations. Reductions in downhole tool reliability will increase dependence on real-time modeling when evaluating and monitoring of downhole conditions. It is vital to have the ability to quickly estimate thermal consequences of whatever well control method is used, which may provide an opportunity to help prevent downhole tool failure caused by extreme temperatures during an unnecessarily slow or prolonged well control event.

Fluid compressibility, like temperature, may be largely ignored while drilling moderately deep and moderately warm formations. However, the combined effects of compressibility and temperature changes possible in extreme HPHT wells can create significant confusion and potential problems. The ability to automatically and simultaneously model both fluid compression and temperature effects makes it much easier to reliably manage critical downhole relationships, while staying within drilling margins, by manipulation of surface pressure, mud density and displacement rates.

Mud rheology challenges, require the use of real-time modeling of affected pressures that can provide an indication of unexpected fluid performance that could force wellbore pressure outside of necessary control limits. By using a hydraulics model during drilling operations that immediately precede a well control event, relative accuracy of the model can be assured just prior to its use during a subsequent, unexpected well control event.

Relatively high equivalent circulating density (ECD), can affect long, small-diameter hole sections. Very high formation pressures are generally encountered only in deep wells, which likely also include zones of significantly lower pressures. To ensure proper annular flow barriers, hole stability and kick tolerance, these wells often require many casing and/or liner strings. This can result in a relatively small-diameter but perhaps fairly long open hole in the extreme HPHT sections. Along with high rheological values typical of very dense muds, this creates conditions for very high annulus friction, or ECD values, as well as significant possible gel effects.

Large wellbore fluid volumes, with long displacement times, require advanced modeling techniques together with downhole tools to reduce dependence on surface measurements, which is key to their ability to improve overall drilling efficiencies. The large fluid volumes contained in very deep wells have a substantial impact on crucial displacement measurements, such as deep cement plug displacement volume. Volume changes caused by temperature changes, which can impact kick detection practices, also increase in proportion to well volume.

A good example of an advanced extreme HTHP automated well control software is SafeKick’s SafeVision Well Control Package, whch was developed to provide benefits during conventional well control operations, but its features may also help to manage extreme HPHT wells.

Source: SafeKick and Drilling Contractor