Private Forums
Cement excess to use when Drilling-with-Casing
22 March 2019
Dear all

As a further derivation of a previous thread (,
here's one to get your teeth into.

At a recent DWOP that we facilitated (our 438th Workshop!!), one of the groups was challenged to decide what cement excess to use for a 13⅜" casing (drilled with 17" OD drill-shoe).  It is required to get cement to seabed, because the HP wellhead housing will be installed on the top off this casing (swedged over).

The thread that I referred to above (6392) asks several questions, including how to determine excess to use when there is no caliper information available.

We do plan to pump a fluid caliper, but I'm left wondering what technology is out there and/or what empirical data you might have based on actual cement jobs conducted.

Many thanks


4 answer(s)
General Manager
Total Posts: 17
Join Date: 27/02/16


With regards to your question: … what empirical data you might have based on actual cement jobs conducted?

It is not rare that we recommend our client to post-analyse their Bit-BHA runs (directional wells) to derive both Bit Steerability (a function of rock strength and bit geometry) and Bore Hole over gauge (OVG), as fitting parameters to the Bit-BHA directional performance.

The job consists in segmenting the Bit-BHA run according to the different formations drilled deriving Bit Steerability, then sub-segment within a given formation the Bit-BHA run according to the steering parameters (Steering Vector / % activation – Slide & Rotate data) and derive OVG and local dog-legs (Bit-BHA geometry & Stiffness, MW, Trajectory, Drilling parameters considered). The process has been automated making it valuable to adapt on the fly the planned Casing String RIH job TnDnB and Centralizers’ placement as well cement volumes from that derived pseudo calliper log.

Note that the process doesn’t not consider borehole erosion over time. But it gives insights into order of magnitude of potential caves and weak formations OVG.



Drilling Specialist/Well Engineer/Training Consultant
Kingdom Drilling
Total Posts: 389
Join Date: 10/01/05

I'm assuming this is a slender well and the 13 5/8 is a surface casing string required to be cemented to surface to provide the well foundation structure and integrity demanded. Also that a conductor has been set at a preferred and deep enough depth such that cement will not broach at the conductor shoe. 

The formations to be cemented, local knowledge and experience  are central and key. Water depth also plays a big part. e.g. in a clay dominant environment simple class G will work fine (this has been proved time and time again in many deep and ultra deep water environments). Where silts/sands are presented formations strengths can be significantly weaker. In interbedded sequences hole condition may not be as effective as required and greater excesses etc may be required.

Offset wells generally should evidently present what works and does not for each region, set of environments conditions and situations one may have.

With standard class G cement and surface strings we simply pump a light weight slurry until we see affirm and confirm returns at the seabed, (there are several ways means tools and equipment to do this). There is no magic number or way to ascertain what volumes is required, as it will vary from job to job even in the same region. Even with these wells, at times is it difficult to be sure if cement returns are observed or not. (visibility can be a problem). An ROV tool and the expense of this may be a better way. 

Once affirmed and assured we change to the heavier weight slurry volume that we then pump and displace around the surface casing shoe.

When stratigraphy and conditions present a risk of not getting cement back to seabed with conventional cement. This is the central and key issue to be sure of in each and every well. (e.g. on one well in 10 you drill through a large unconsolidated sand interval, then what works in a clay dominant sequence will not work in sand w.r.t cement) Then your options are  

•Add ‘Sized particles’ cement technology
1.Nitrogen (foam)
2.Lightweight microspheres or beads.
Advantages/disadvantages of each must be considered.

If you want to get good cement to surface.
Personally for me foam is too complicated for surface jobs and if there is no shallow flow (water/gas/hydrate) risks present then Lightweight microspheres or beads slurries work best for the lead. Cement companies can provided hundreds of successful application of this. 
There is a higher price but cement to seabed assurance is the price one may have to pay versus well fatigue problems or an APB channeling conduit that in theory could later result during later well0life cycle operating life.

If you are 'casing while drilling' this string to bottom. My understanding is that wellbore condition will be more likely better than conventional.  (les prone to enlargement and washout). This should increase likeliness of too much cement needed and excesses required. In theory. 

In practice as stated there are best practices mean methods and way to assure good cement reaches seabed and more importantly perhaps is spotted at the surface casing shoe.

SPREAD Associates
Total Posts: 3
Join Date: 25/02/19
I cannot really add much to what Paul states, all good.  

My experience with casing-drilling in South Texas, we used the same excess %'s as in normal drilling scenarios.  ie, surface pipe was 100% excess, intermediate (7" x 8¾") was 30%.  Same for the one project I was involved with in Oman, which was a 9⅝" x 12¼" planned at 35% (they never actually got to bottom w/casing-drilling gear.) The intermediate casings, however, did not have any specific TOC requirements so were not critical as in your case.

  • I agree with the fluid caliper, although I personally believe their usefulness is limited, but better than nothing at all. In addition to whatever other contrasts you design into it, be sure to add some viscosity difference to minimize it's getting strung out up/down the hole while circulating.
  • Likewise if possible to do inner-string, much simpler and no need for guesswork. simply pump cement until visible at mudline. I suppose this depends to some degree on the type of BHA being used.
  • Also agreed on a near-surface stage tool, as a contingency, maybe around 500' below mudline. rather than a regular DV, however, suggest a sleeve-type which can be shifted with a workstring and doesn't need plugs. That way if it's needed you're not dependent on pushing plugs down; and if not needed simply move forward without activating.
Cautionary note on the stage tool, if your DwC setup involves rotating (torque) from surface, then the stage tool may become a weak point in the string. check carefully.

Last comment, and I'm sure you've thought of this already, have a contingency ready in event a top-job is needed. Afraid I can't offer any thoughts on this without knowing more about the setup.

And yes, would love to know how things turn out.
Total Posts: 99
Join Date: 10/04/08

As you know several of us responded on this subject before and it seemed nothing existed to do a real-time caliper log whilst running casing which would apply to drilling with casing as well I should imagine. 

Given you need to get cement to the seabed to support load, you probably need to treat it like a larger casing/conductor cement job and pump significant amounts of excess cement to be sure you get it to the seabed, especially in the absence of real known data.

A fluid caliper of some kind will help.

I wondered if you could assure getting cement to the seabed by doing the cement job as an inner string cementation, sealed into casing with drill pipe towards the bottom of the string so that you pump cement until you observe the returns at the seabed, or run a contingency 13⅜" mechanical two stage collar so you can do a top up job if you get losses or insufficient cement height.

Let us know how you decide to progress.
Jump to top of the page