we are planning a reverse cement Job for 24" casing run in 28" hole size, the previous casing is 26" - ID - 25"
26" casing setting depth - 2700ft
24" casing setting depth 3650ft.
The Top of cement behind 24" casing is 2300ft. covering a big loss zone.
FG at 24" casing depth 10.5ppg
MW drilling was 9.1 ppg
I appreciate your help understanding what way to go- Conventional cementation or Reverse cementing.
What are the Hi-points or Low points for Both.
What is achievable having good cement bond behind casing covering the loss Zone.
If anyone has case studies , SPE papers kindly share.
Appreciate your help
Thanks & Best Regards,
I have not reverse cemented, but it is an interesting conversation. I think if you start with the objectives of your cement job, the solution will follow. Usually, the objective is sufficient shoe strength / leak-off, to drill the next section. This objective implies that you want your strongest, least contaminated cement, around your shoe, which is achieved by conventional cementing.
One of the disadvantages of conventional cementing is that as the cement raises in the annulus there is an important increase in hydrostatic obviously, but there is also an important contribution of friction pressure coming from the annular gap derived from the higher rheology of the cement slurry; the geometry of the flow path along the annulus (as described by the caliper log, min and max hole diameter, etc.) and surface return lines. This is not normally a problem, but if in a losses situation the cement would be inclined to take the path of minimum resistant, typically the losses zone, stopping its way going up in the annulus. All this is easily simulated (predicted) by the cementing company's software, and there are several alternatives to "prevent" it both embedded in the design or more of operational mitigations. The bad thing is that all this prevention or mitigation would act contrary to the main objective of primary cementing, which is mud displacement. (You know for cement slurry to displace the mud efficiently, the slurry needs to be higher density and has higher rheology).
Anyway, one "nice" alternative to remove all that friction pressure in your annulus pushing the cement to the losses zone is Reverse Cementing. Here the friction pressure is acting from or against the top (rather than from or against the bottom). In other words friction pressure would be helping you to "reduce" the hydrostatic (more like the ECD) acting on the losses zone. That is the principle. Additionally since you are pushing your mud from the top with cement, both density and rheology of the cement slurry can be (must be actually) lowered in order to achieve proper mud displacement. In this direction of flow, a heavier (than your mud) slurry would be driven by gravity (channeling, sinking) damaging your mud displacement, but a lighter slurry would try to always stay on top displacing your mud more evenly. This has an obvious effect on your annulus hydrostatic and what ECD would your losses zone see.
In general, cement bond quality in reverse cementing would be worse that conventional cementing, BUT in a case of losses situation reverse cementing has greater chances to allow you to cover your annulus with cement and allow you to attain your TOC.
The keys for reverse cementing are: Proper design of cement slurries for this condition and your casing hardware. Collar and shoe, to allow reverse flow; and good centralization (centralization here has a greater role than in conventional cementing).
I believe that this simple explanation in addition to Clayton's and Steve's would give you a good starting point to understand which way is better in your case.
The cementing company software simulation can be used to better evaluate the different scenarios, but not all available simulators can handle the simulation of reverse cementing. One of the big ones certainly can; and another won't encourage you to do it at all, but to be honest with the lower quality of cementing engineering support theses days, I would include that as a factor to consider.