Casing Drilling Reduces Surface Sections Duration by 50%

Abstract?

This article covers the successful application of non-retrievable casing drilling technology in surface sections.

Background?

We experienced total losses, wellbore collapse, and bit balling issues within the first 150 m.

The big (up to 2 in) and poorly consolidated boulders fell on top of our drill-pipe conveyed assemblies and increased the likelihood of getting mechanically stuck. We drilled this interval using thick mud to improve the carrying capacity and low flow rates to avoid washing out the hole.?

The reactive shale underneath this interval required the opposite approach; the use of thin mud mixed with ecofriendly surfactant and high flow rates. To make matters worse, it was difficult recognizing?when the transition between these two lithologies occurred, which led to bit balling issues and additional trips.

The remainder of the section was composed by interbedded sand and shale layers that did not present any major operational issues.?

Design?

We used computer software for running hydraulics, torque, and drag models, and helping us envision the ideal operation. We fed these using offsets surveys, sliding sheets, drilling logs, and mud checks, among others.

We designed these jobs for using flow rates in excess of 400 gpm and limiting the penetration rate to 50 mph. We anticipated total pressure losses of 800 psi, equivalent circulating densities of 9.7 ppg EMW, and very good hole cleaning indexes. We did not expect buckling or exceeding torque limits during drilling or tripping.

Risks

We implemented multiple safeguards for mitigating risks such as:

• Casing bit wear
• Casing bit balling
• Plugged nozzles
• Washed out floating equipment
• Casing and connection failure
• Casing stuck with big boulders
• Higher swab and surge pressures
• Higher equivalent circulating densities
• Cement slurry flash-setting (nozzles)
• Next section bit damage during drill-out

Trade-Offs

We traded-off the followings to achieve the objective of reducing the phase time.

• Casing stand-off reduction
• No directional surveys
• No open hole wireline logs

Surface Equipment

The rig did not require any modification.

We made-up a casing running tool to the top drive system to have the capability to rotate and make-up the casing string.?We had a set of link tilt arms with single joint elevators to pick the joints out of the pipe wrangler and stab them onto the string set on slips. We used hydraulic slips to improve both safety and performance efficiency.

We used one rig pump for drilling and the other for jetting the returns out of the cellar hole.

Drilling Assembly

The non-retrievable drilling assembly was entirely conveyed with 9-5/8 in casing.

The float valve had a 4-1/4 in diameter valve to ensure the highest possible flow rate capacity, thus minimizing float wash-out events. We used a single non-rotating plug system for cement displacement.

The bit was manufactured with drillable materials and welded to 3 feet long pup joints. It was designed for medium to hard applications to minimize the chances of damaging it within the boulders interval. We minimized the blade count and cutters density to easily drilling-it-out using standard bits.

We did not have deviation issues despite the fact we did not run stabilizers.?

The wellhead bottom pin connection exceeded the well requirements for tension, torque, and pressure, thus easing both make-up and landing operations.

Procedure

We used this procedure on every well:

1. Performed rig-up
2. Held pre-spud meeting
3. Picked-up the casing drilling assembly
4. Drilled with casing to total depth
5. Performed the cement job
6. Installed the wellhead A section
7. Installed the blowout preventer equipment
8. Drilled-out the shoe track
9. Continued with the next phase operations

Improvements?

The higher annular velocity improved the boulders carrying capacity, the smearing effect built stronger filter cake that avoided both losses and collapses along the boulders interval, and the higher flow rate avoided balling issues and improved the rate of penetration by 40%.

Smearing Effect

We had less and much smaller cuttings, as these were smeared and grinded downhole by the action of the casing pressing them against the wellbore wall multiple times before arriving to the surface. We evidenced the benefits of the smearing effect, thus reducing mud, solids control, cement, and logistics costs.

Well Control

We did not take any kick.?We only used the water based mud hydrostatic for well control purposes as there was no blowout preventer equipment installed.

We exercised higher well control awareness as we had smaller annular clearances than when running drill-pipe assisted assemblies. We trained drillers on correct connection practices to minimize swab and surge pressures.

Results

The implementation of the non-retrievable technology for drilling surface sections quickly ended-up being economical.?We drilled dozens of wells, reducing the phase time by 50% and breaking-even the additional expenses with time savings.

Get in touch at [email protected] if you would like to discuss in detail the value I can add to your team.