Oil and Gas
Gilsonite is a naturally occurring asphaltite, having specific gravity substantially equivalent to that of water.
Cross reference ice while it is of very light weight in comparison to most solids, it is not porous. Unlike perlite, which is presently employed as an aggregate for the lightening of oil and gas well cement, it does not absorb water, nor is it even wet by water. Thus, I have found that water requirements for making acceptable cement slurry, which may be easily placed as required and which will set firmly and permanently, are considerably less than those of perlite as an addition agent. I have found, moreover, that the strength of the set cement is greater than with perlite.
In the present composition, the Gilsonite serves as an aggregate which lightens the cement-water slurry, imparts valuable lubricating properties that reduce abrasiveness of the slurry, replaces a large portion of the cement ingredient and reduces shrinkage of the setting cement composition to an unusual extent, reduces compressibility of the set cement composition when in place, and insulates against undesirable loss or gain of heat by the well.
Additional objects and features of the invention will become apparent from the following detailed description of preferred formulations thereof.
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. The finer aggregate also forms,