What is amorphous graphite?
amorphous graphite is a solid, black, bituminous material which is found in significant quantities in certain subterranean, hydrocarbon-containing reservoirs.
The reservoirs are carbonate reservoirs and some sandstone reservoirs.The reservoirs which we have examined typically contain between 0.1 wt. % and 10 wt. % graphite.
The graphite is typically present as a filling or lining within vugular and inter-crystalline pore networks and fractures. It is generally accepted that amorphous was formed in-situ by either thermal alteration of oil or de-asphalting of heavy oil.
The amorphous is an impediment to hydrocarbon productivity because of its oil-wetness, porosity occlusion and permeability reduction characteristics.
It is the objective of the present invention to improve the effective permeability of the reservoir rock and enhance the producibility of a well completed in the reservoir, by removing amorphous graphite.
A graphite impregnated coating on any of the advantages normally accruing to graphite, namely, low friction, non-reactive, non-polluting, and electrically conductive.
Various types of graphite
Various types of graphites may be utilized, such as natural flake, natural amorphous and synthetic graphites. However special methods must be used to form a durable coating. Foremost among the problems in forming a coating is that it is difficult to adhere graphite to surfaces due, in part, to the fact graphite does not have an electric charge and there is a weak bond between the platy crystals. In contrast, most minerals are, overall, electronegative, and some minerals have both electronegative and electropositive charges within the same particle.
Binding of graphite
Consequently, it is essential that the coating comprise a binder, preferably a resin or polymer, that encapsulates the graphite and adheres to the substrate. Therefore it is an important part of the process to disperse graphite in a binder so that when cured (by, e.g., temperature, catalyst or evaporation of water and/or organic solvent), the graphite/binder mixture will adhere to the substrate to the extent and time required by the application. As will be shown, the binder can be a water soluble polymer, water-based emulsion or solvent-based hydrocarbon.
Binders may include organic film-forming resins, such as alkyds, polyurethanes and epoxies; film-forming water-soluble polymers, such as starch, carboxymethylcellulose (CMC), hydroxyethyl cellulose (HEC) and xanthan gum (XC polymers); resin-dispersed emulsions, such as latex and acrylics; or waxes and paraffins.
Spraying or commingling substrates with just enough binder and graphite works well for coating small particles. The preferred method is an appropriately sized mixer or blender where air or heat can accelerate the time to make a quality uniform coating. Two or three thin coatings give a better quality coating than can be normally obtained with one heavy coat.
In the case of particulates, the procedure involves adding a known amount of Slip (a pre-mixed formulation of graphite and resin available from the Superior Graphite, to a known weight of nut hulls (or other substrate), mixing until dry to the touch, and then adding more of the formulated graphite and binder. This routine is repeated until the desired amount of coating has been applied. The amount of graphite/binder is calculated from the increase in weight over the original.
The inverse procedure also works well, that is adding the nut hulls (or any other substrate) to a known amount of binder. As the resin permeates into the substrate and begins to polymerize, graphite is added. However, this method however adds another step, in that excess graphite that does not stay attached to the substrate must be removed.
Amorphos graphite coating
The substrates identified can be coated with a variety of binders, and the coated particles can range in size from approximately +20 microns to −6.3 millimeters. The thickness of the coating may vary from approximately 3 mils (0.076 millimeters) to three times the diameter of the particle being coated. The weight percentage (wt. %) of the graphite relative to the substrate can vary from between less than 1 wt. % to 97 wt. %, and more preferably from about 5 wt % to 95 wt. %.
Ceramic beads can be coated with an epoxy resin containing 30 wt % graphite. Alternatively, ceramic beads can be coated with water soluble mixture of a high amylopectin starch and NaCMC dispersed in de-ionized water, in which the branched chain glucoside provides stronger adhesion to the bead than the more common amylase starch. The starch was followed by the addition of a small amounts of Na—CMC and glutaraldehyde as a biocide for storage stability.
CMC is anionic. The hydrated colloids will adsorb on any electropositive site regardless of their composition. This adds “toughness” to the dried binder thus keeping the graphite on the bead surface following removal of free water (e.g., be heating to 135° F.).
Percentage of amorphose graphite usage
A material may be treated with less than 1 to about 50 wt. % graphite. The treatment may be a partial coating or it may be a graphite film up to about 15 mil (38.1 millimeters) thickness. In some applications it has been found useful to disperse graphite in a resin or polymer binder for extreme long term service in water or oil, or it can be formulated for temporary service wherein the binder containing graphite is dissolved in the fluid in which it is being transmitted downhole, thus freeing the graphite from the high performance particulate solid. In that case the graphite may be as much as 97 wt. %. However, the use of graphite treated particulate is not just a method for introducing graphite but is for also improving the performance of the base material with which it is associated.
Drill-In and Completion Fluid Additives
Current completion fluids technology often makes use of sized calcium carbonate particles to reduce fluid loss into the pay zone when high purity, high density brine, such as zinc/calcium bromide or cesium/potassium formate, is used to complete a well.
One problem with the use of calcium carbonate particles is the increase in pumping friction by virtue of the mass of particles colliding with each other as they are pumped with the brine into the wellbore. This problem has been recognized by oil companies as needing improvement. In any case, a significant increase in pumping efficiency is realized with the graphite coated particles, particularly in horizontally drilled wells several thousand feet long.
Caoting calcium carbonate
Coating the calcium carbonate reduces the coefficient of friction from about 0.3 to 0.08, and the graphite-coating of the calcium carbonate particles has no measurable effect on rheology over uncoated particles. Calcium carbonate is 100% soluble in 15% HCl mud acid. The calcium carbonate is sized to plug the throat of pores in the producing zone and may be used in a concentration of 10-25 lb/bbl or more. When the well is allowed to flow, the graphite-coated material will be forced out of the pores by produced oil coming into the production string. However, calcium carbonate with a temporary thin coating of graphite, once in place on the producing formation, can still dissolve with acid. Because of the oleophilic surface of graphite, it is likely that the graphite coated calcium carbonate will come out of the pores more easily than the uncoated mineral.
Amorphose graphite as hydrophilic polymer
In some drill-in and completions, hydrophilic polymers such as XC-polymer (or xanthan gum), starch or hydroxyethylcellulose (collectively known as WSPs (Water Soluble Polymers)) may be used along with the calcium carbonate to give a very low API fluid loss of less than 1-ml/30-min.
The life of the graphite coating can be controlled by varying the type and composition of binder. For short term life of about one hour or less, a water-soluble binder made from starch and hydroxyethylcellulose may be used. For a coating life of several hours, a binder made with a permeable film such as an acrylic emulsion may work best.
For a long-lived coating with high resistance to water, a graphite-filled epoxy-based coating may be preferred. In each case, the likelihood of formation damage due to graphite content of the coating is minimal for two reasons: 1) the graphite is of extremely fine particle size (<10 micron), and 2) the weight percent graphite per particle can be down to the level of a minor contaminant.
Application of graphite
amorphous in oil well drilling
It is using for oil well drilling fluid
amorphous in foundry
It is using to make smooth surface
graphite in mix with asphalt
It is using to increase hardness of asphalt
Packing of amorphous
We supply amorphous graphite packed in 25Kg bag in 30-40 mesh also 200 mesh and 325 mesh or in raw form in rock or lump packed in jumbo bag.
Analysis of material
|NO.||Test (wt%)||Test method||Test result|
|1||Ash content||ASTM- D3174||1~15%|
|2||Moisture content||ASTM- D3174||1%|
|3||Solubility in CS2||ASTM-D4||85~98|
|4||Volatile matler 900C/min||ASTM 3175||44|