Remember when we were still able to do this? These images were taken a little over a year ago on my third rig visit to Oman and they were part that helped me shape my view of the short time I’ve spent in the industry. Trading my bread and cheese & normal office hours for, well… whatever they had on the rig to very erratic working hours. Hard to describe to your loved one back home what life on the rig is, but I think that the short video in the link shows it well. All in all, an amazing experience and can’t wait to get back out.
Would you like to know on which job we were working? Check this link out: //ed-projects.com/oman-case-study-2020/.
A guideline to create a wider understanding of the many variables involved in the selection and optimisation of stabilisers in the BHA.
G.P.O. Guideline: for Optimal Stabiliser Performance.
The job description of a drill string stabiliser is multi-functional, its main function is to stabilise the bottom hole assembly (BHA) in the wellbore, while enabling the drill string weight and rotary torque to be transferred past the stabilisation point with the minimum amount of weight and energy loss. The blade design should enable drilling fluid and the transportation of drilled cuttings past the stabiliser as efficiently as possible. In addition, the profile of the blades should allow interaction with the borehole wall, minimising the amount of shock and vibration generated when stabilisers with sharp edges collide with the formation, this scraping action can severely damage the filter-cake.
Although widely acknowledged as an essential component of any BHA, the stabiliser is still often overlooked. If properly designed the stabiliser will also contribute to improvements in performance. This is achieved by enhancing BHA stability in the borehole, minimising rotary torque and vibration and maximising energy transfer to the bit.
Image 1: Role of stabilizer in BHA vibration with a reference image from a paper from Fred Dupriest: “Thus, the lowly stabilizer”
When optimising the sometimes-complex process of BHA stability, bearing in mind the many variables such as wellbore trajectory and profile, formation type, possible borehole instability, bit selection, drive type, and maximum drill-string RPM. It is obvious there are too many compromises in a one-fits-all scenario.
To help simple BHA stabilisation and stabiliser selection, we highlight 3 areas that require additional attention;
- Geometry, i.e. the taper angle, blade profile, and flow-by area
- Position of the stabiliser in the BHA, to optimise BHA stability and minimise whirl and vibration
- Optimal outer diameter of the stabiliser blades, to avoid too close to gauge stabilisers from pinching on the borehole spiral patterns when POOH. Make allow for the difference between actual borehole diameter and effective borehole diameter
G – Geometry:
Orientation, position, and profile of the blades (dome profile, no sharp edges) are all part of the design features of this different type of stabiliser. The 17-1/2” and 16” Switchblade and Fixedblade stabiliser have 8 blades, the 12-1/4” size and under all have 6 blades, this fore and aft blade configuration ensures all-round contact with the wellbore, improving BHA stability while providing a low pad pressure on the formation. The dome profile of the blades creates a plastering effect on the filter cake when rotating which compresses and limits the further growth of the wall cake.
The area profile between the two sets of blades creates a jetting effect accelerating the fluid and drilled cuttings around the blades, reducing the tendency of cuttings to accumulate build-up. The open profile, low pad-pressure, and spacing of the blades enable this design stabiliser to displace and bypass cuttings accumulated in cutting beds, with ease compared to the conventional spiral blade design.
Image 2: Front view Fixedblade stabiliser with a reference image from a paper from Fred Dupriest: “Thus, the lowly stabilizer”
P – Position:
The optimal position of stabilisers in the BHA will change depending on the application i.e. hole size, well profile and trajectory, drive type, and maximum drill string rotational speed.
Contrary to common belief, vertical wells require equal attention to stabilization and stabilization points, if not more, than deviated wells, if downhole drilling dysfunctions are to be maintained at a manageable level. Inadequate BHA stabilization is also the main cause of Bit, and BHA whirl, resulting in shorter life cycles of downhole tools and compromised quality of the wellbore. Borehole spiralling, in turn, often leads to problems pulling out of the hole. This is particularly valid when the initial period and following spacing is neglected and close to gauge stabilisers end up pinching on the borehole spiral patterns.
Since the average diameter of a spirals hole is under gauge, spirals borehole patterns can create problems when running casing.
Never use a pendulum assembly to drill a vertical wellbore, it generates excessive lateral shocks and vibration. This theory is backed up by a quote from Fred Dupriest: “packed good, pendulum bad”.
The position and outer diameter of stabiliser in deviated hole-sections will differ depending on drive type i.e. motor or RSS.
For motor applications the outer diameter of the stabiliser positioned above the motor suitably under gauge to maintain a build or hold trajectory when drilling in the rotary mode.
For this application our Switchblade stabiliser is an ideal choice, as the OD of the blades can be varied by one inch in increments of 1/8” of an inch, enabling the operator to fine-tune the assembly to suit the required build rate when drilling in the rotary mode.
To improve BHA stability and minimise whirl when rotating, we recommend having at least two stabilisation points above the motor (observing critical rotary speed windows will improve performance and minimise tool failures).
Likewise, when drilling with an RSS we always recommend at least two stabilisation points above the RSS to minimise BHA whirl, which is the main cause of borehole spiral patterns, and the main contributor to time-consuming back reaming issues, when close to gauge stabilisers pinch and hang-up on the spiral profiles when pulling out of the hole.
Again, observing critical rotary speed windows are important. There is a tendency when drilling with RSS systems, to compensate for the combined bit speed of the motor- drill string combination, by rotating the drill string at speeds above the critical rotary speed threshold overlooking the centrifugal forces and buffeting created as a result of the excessive rotary speeds.
O – Outer diameter:
The outer diameter and the position of stabilisers for deviated hole-sections will differ depending on the drive type, i.e. RSS or Motor.
For motor applications, the outer diameter of the stabiliser positioned above the motor will depend on the well-plan for the section i.e. build only or build and hold.
For a build only section, the outer diameter of the stabiliser above the motor should be gauged so the assembly has a build tendency when drilling in rotary mode, reducing the number of slides required to reach the planed hole angle, this practice will deliver a smoother build-up curve.
Motor assemblies for build and hold sections requires more finesse and a degree of local knowledge to fine-tune the assembly to where it has a slight build or neutral tendency in rotary mode. If the assembly has a dropping trend when rotating it will require additional upward slides to maintain the angle and produce a more tortuous build section.
For RSS applications, some RSS systems are more inclined to create borehole spiralling than others, yet they still continue to run stabilisers 1/8” of an inch = 3mm under gauge.
If you can minimise borehole spiral patterns when drilling, you will improve performance by minimising friction and consequently improving weight and energy transfer to the bit.
Spiral patterns in the borehole are also the main cause of tight hole problems when POOH, when too close to gauge stabilizers pinch on the spiral profiles.
All boreholes have spiral patterns to some degree, this fact should be considered when selecting the optimum outer diameter of stabilisers for your particular application.
Sufficient stabilisation points strategically placed in the BHA will minimize BHA whirl and spiral hole patterns.
The geometry of the stabilisers should be an important part of stabiliser selection. The profile of the blades (no sharp edges), the wrap angle (should have a clear line of sight and preferably an open profile) and an optimum taper angle of 30 degrees or below should be taken into account (Most is well documented by Paul Pastusek in ExxonMobil’s stabiliser guidelines).
Critical rotary speeds windows and optimum flow rates for hole cleaning should always be taken into consideration. Moreover, there is a balance that must be reached between the optimum rotary speed to clean the hole and damaging centrifugal forces created by detrimental rotary speeds.
It’s all about balance.
Hope this helps.
A more personal interview talking about where ED-Projects mission came from and where we are going.
Staying positive in the downturn is a challenge, however, we have been here before. In 1986 & 1998 oil prices got to $14 and $12 a barrel respectively, we battened down the hatches and weathered the storm by improvement in technology and becoming more efficient.
Nobody knows where this is going or how long it will take, however, we do know at this moment in time there is no alternative for fossil fuel and that the future lies in innovation.
We wish you all the best in this challenging period.
Hey Tom! Episode 5 – in this episode we are talking about the importance of adequate stabilization points behind a rotary steerable system. This topic came to existence after numerous runs in the Middle-East and Europe, where did see a significant difference in the overall performance and wear on tools.
Also, we will be Aberdeen until Wednesday the 19th and leaving for London on the 20th. We still have a few hours left unscheduled, so if you would like to have a chat, please leave a message.
New Partnership in Kurdistan
We are delighted to announce that we have recently teamed up with Independent Oil Tools (IOT) in the region of Kurdistan. IOT will represent and supply our innovative range of stabilizers and reamers in Iraq and will help us strengthen our presence. We are proud to have already established a proven track record in the country as well as the region with our unique hydrodynamic design tools and look forward to expand our offerings and partnerships through this new collaboration.
EDP Fixedblade design stabilizers are building momentum in the Kurdistan region!
According to one of the operators, based on previous experience, there was a 50% chance of getting stuck when running solely conventional spiral blade stabilizers in the drillstring. Upon gradually switching from conventional design stabilizers to EDP Fixedblade design improvements are unmistakable. After 2 years of integrating our design of stabilizers into their drill strings, the operator reported they had only experienced 2 stuck pipe incidents and no LIH cases.
Additional goals and design benefits are improved weight & energy transfer, reduced vibrations and enhanced transportation of cuttings around the tool.
Presently, our offering includes 17 1/4″, 12″, 8 1/4″, 5 3/4″ string stabilizers in addition to a range of Nearbit and Bitbox sizes.
Hey Tom! Episode 4 – in this episode Tom is talking about how performance means different things to different people. For the driller, it means drilling more meters than his back-to-back. For the bit provider, it means getting more ROP than his competitors. ED-Project’s KPI is to minimise back reaming by effective stabilisation which counteracts the reactive torque from the large cutter PDC bit. In this particular section, the total back reaming time while POOH was 26 minutes.
It is that time of the year again and we are planning our trip to ADIPEC; we are looking forward to seeing you, please come by our stand and say hello. This year, in addition to our Switchblade and Fixedblade Stabilizers, we are exhibiting our recently launched LK Reamer which can be configured as a Reamer, a Stabilizer or a combination of both. We are located in hall 8 stand number 8336 in the UK sector.
In this video, Tom explains more about downhole spiralling problems.
In this video, Tom is explaining the advantages of running stabilizers ¼” under-gauge in comparison to 1/8”. Running stabilizers too close to gauge can cause pinch points coming out of a hole which we know is not cylindrical. Remember: 1/8” only is the width of your door key. Why take the risk? Put the percentages on your side of the table!
Here’s our third episode of Tom explaining what he’s trying to do with our stabilizers. Let us know what you think!