IADC/SPE 27448 "Universal Fluid: A Drilling Fluid to Reduce Lost Circulation and Imporve Cementing", by J. J. Nahm et. al. of Shell.
Various Shell research and operating groups have been working on what they refer to as a 'universal fluid' (UF), which is described as a "water-based fluid that has been treated with finely ground blast furnace slag and that still maintains the appropriate characteristics of a good drilling fluid." This drilling fluid can be 'activated' to set, similar to cement. The ingredient that makes it serve as both a drilling fluid and a cementing material is finely ground yet otherwise ordinary blast furnace slag. The slag is said to be inexpensive, and when it concentrates against a permeable zone in a filter cake, the filter cake effectively solidifies and bonds to the formation in the process, thus yielding excellent seepage control and zonal isolation. Since UF is the same for drilling and for 'cementing', there is not any concern about contamination. Further, it is claimed that any unactivated 'pockets' of the UF will eventually set up over time, and hence there will be no voids in the cement like one may encounter with mud contaminated cement.
In the paper, Shell describes their laboratory testing, first in a test cell and later in a 'full scale' horizontal test section consisting of a 5" O.D. casing in a simulated 6.5" I.D. wellbore. The simulated wellbore was made more realistic by the addition of several enlarged hole sections, (not 'washouts'!). After promising results, the UF/slag mix system was field tested in nine wells, also with good results.
Shell concludes several things, one being that the UF can achieve '100% displacement efficiency'. This is a tall order, but they claim this since the unremoved filter cake and mud will eventually set up nearly as well as the activated slag mix. In short, depending on the economics, this could represent one of the most significant breakthroughs in recent memory.
IADC/SPE 27449 "Evaluation of Blast Furnace Slag Slurries for Oilfield Applicaton", by O.G. Benge et. al. of Mobil E&P.
This paper, which directly followed the one by Shell, presented a laboratory study of their experience with blast furnace slag mixed with muds. Mobil was not nearly so optimistic as to the universal applicability of blast furnace slag. In particular, Mobil found that the slag mix tended to crack significantly after setting a few days. Photos showing gaping cracks in cross-sectioned samples left no doubt that zonal isolation would have been lost with the Mobil samples.
Mobil investigated the uniformity of slag supplies. As this is basically a waste product, it was not surprising to find that the raw material varied substantially in its rate of activation or setting, as measured by the standard cement thickening time tests. For example, samples taken from the same supplier varied in pumping times by as much as two hours for the same slurry 'recipe'. Significantly, samples taken from different suppliers varied as much as five hours in pumping times. In short, Mobil cautioned that the individual batch of raw material supply must be closely monitored.
Mobil questioned the economics of the blast furnace slag mixes. They calculated that unless one was cementing in mud densities over about 16 or 17 ppg, it actually cost more to use the blast furnace slag than to use conventional portland cement.
Other problems Mobil noted were related to safety, (H2S was given off by some slurries), CO2 resistance, (Mobil found the slag mix not to be CO2 resistent), a setting time that was dependent on the shear rate of the mixing, and the possibility of increased corrosion rates on tubulars when compared to conventional cementing.
To summarize, while Mobil recognized that Shell had worked on the systems far more than they had and thus had worked out some of the problems, Mobil in general was not in favor of the system and did not view it as either a 'universal' system nor one that could be run as easily or more so than conventional portland cements.
Who is right? Shell or Mobil? If you have any first, second, or maybe even third hand stories to relate concerning blast furnace slag mixes, please let us know!
IADC/SPE 27452 "Effects of New Generation Drilling Fluids on Drilling Equipment Elastomers", by R. P. Badrak of Hydril
In this paper, Hydril presented results of numerous lab studies that examined the effects of new generation muds on the properties of elastomers. It is well known to those 'skilled in the art' that various elastomers react in somewhat unpredictable manners when faced with long term contact with oils. The reaction of these elastomers to the new synthetic muds was examined.
Unfortunately, Hydril would not examine the various synthetic mud compounds tested, either in the formal presentation, the printed paper, or informal conversations afterwards, citing their desire to maintain a good working relationship with the mud companies who had voluntarily supplied mud samples for the tests. However, two factors emerged from the testing. First, most of the elastomers performed as well or better in the presence of the synthetic based muds as they did in diesel based mud, (or to be more accurate, in the presence of #2 diesel). That is the good news. Seond, however, depending on the test being conducted, there were generally one to three muds that degraded the performance of the elastormers significantly.
The bottom line on this paper is that if you are going to be using a synthetic based fluid, particularly one that has not seen much field experience, you should explicitly have the mud company and the BOP company (or other rubber goods supplier), get together and determine whether or not the drilling fluid and the elastomers are compatible. It also means one must be extra careful of the rubber goods if non-OEM spare parts are used!