Cementing Gilsonite – Since Gilsonite, a solid hydrocarbon, was introduced to the oil industry in August 1957 as a cement additive, several thousands of jobs have been performed using the material. These operations have included primary cementing through lost-circulation zones of surface, intermediate, and production pipe in both single and multiple stages as well as various remedial jobs such as squeezing, re-cementing above inadequate fill-up, and plugging back to reestablish drilling-fluid circulation. Designed primarily as a combination low-density lost-circulation slurry, Gilsonite has yielded excellent results in areas of incompetent formations as well as in other types of lost-circulation zones. Field results generally show that fill-up of 80 to 90 percent can be obtained in areas where only 50 to 60 percent fill-up was possible with other types of slurries.
The unique properties of Gilsonite:
resistance to corrosive fluids
low specific gravity
low chemical inertness
low water requirements cause a slurry containing exceptional bridging properties
low slurry weight
Compatibility with other slurry additives and relatively high compressive strength when compared to other slurries of the same weight.
Gilsonite Cementing Grade has a low specific gravity, is non-porous, and impermeable. The addition of Gilsonite to cement slurries reduces the slurry weight without requiring large additions of water. The result is a superior lightweight slurry, having good compressive strength, which is especially suited for cementing weak formations and in control of lost circulation.
.As the oil-producing industry has incessant grow, the necessity for a low-density cementing slurry possessing lost-circulation control characteristics has become more and more obvious Introduction of Gilsonite
Especially in primal cementing due to the need to reduce remedial cementing operations and the different types of formations existence encountered
These problem formations may range from either porous or cavernous formations to very weak formations that are unable to support the hydrostatic head that is necessary for drilling and well supplementation. This recent type of formation will often break down or fracture under hydrostatic loading, terminating in partial or complete loss of flow.
Cementing of oil well
A cement produced by Gilsonite is suitable for blocking or plugging an abandoned pipeline or back filling a mine shaft, tunnel or excavations contains Portland cement or a mixture of at least two components selected from Portland cement, A cementations slurry, formulated from the cement mix, may have a density less than or equal to 1500 kg/m3, and exhibits good compressive strength.
In the formulation of the cementing composition of the invention, it is preferable to employ Gilsonite in an amount ranging from approximately one-half to approximately ten times by volume the amount of the cement utilized, depending upon the particular result desired.
The lower range is employed where maximum strength is important; the higher range where the various qualities imparted by the Gilsonite are most important.
Particle size and particle size distribution of the Gilsonite determine the strength and porosity-permeability characteristics of the set cement for any given mix ratio.
Where maximum strength is desirable, a coarse Gilsonite Where lightest weight and lowest porosity-permeability are important and strength is to be sacrificed or is of little importance, an aggregate of minus 50 mesh or finer may be used.
Conditions are often encountered in the field requiring various combinations of particle size and particle size distribution. The above examples represent extremes. The mix must, however, always be pump able through the system from the mixing point to the final point of placement of the cement slurry. The coarser the aggregate, the less that may be present in any given slurry without impeding pump ability.
For example, a cement-Gilsonite ration of 1:4, using the coarse aggregate specified above, is difficult to pump and is likely to plug restricted passages in the system, whereas the same mix, using the fine aggregate specified above, will never plug if the water-cement ratio is high enough.
An amount of a petroleum solvent which depends upon the amount of Gilsonite present, may be added to the wet or dry mix for wetting the surface of the Gilsonite particles and causing them to form an intimate bond with casing and earth formations of the bore hole, thus preventing corrosion and minimizing pulling away of the cement from the casing and/or bore hole wall by reason of the shrinkage normal to setting of the cement.
Instead of adding the solvent directly to the mix, it may be pumped through the casing and into the cementing zone in advance of the Gilsonite-cement slurry.