The present invention relates to proppant pellets prepared by using alumina-silica containing waste materials from industrial processes. The proppant pellets may be resin coated. The present invention further relates to a method for the manufacture of proppant pellets.
In the completion and operation of oil wells, gas wells, water wells, and similar boreholes, it frequently is desirable to alter the producing characteristics of the formation by treating the well. Many such treatments involve the use of particulate material. For example, in hydraulic fracturing, particles called proppants are used to maintain the fracture in a propped condition. In hydraulic fracturing, proppant particles under high closure stress tend to fragment and disintegrate. At closure stresses above about 5,000 psi, silica sand, the most common proppant, is not normally employed due to its propensity to disintegrate. The resulting fines from this disintegration migrate and plug the interstitial flow passages in the propped interval. These migratory fines drastically reduce the permeability of the propped fracture. Since closure stress varies directly with depth, this means that sand is not a useful proppant material at depths greater than about 5,000 feet.
Sintered bauxite or high grade alumina have been used as proppant materials at well depths greater than 20,000 feet, but these high strength proppants have much higher densities than sand and therefore require high viscosity pumping fluids or high pumping rates. Larger pumping equipment is required, and wear rates on fluid carrying equipment is accelerated. In addition, the raw materials used to make the proppant materials are more costly.
Proppants of intermediate density are known, and work well in the intermediate depths and pressures, i.e., 7,000 to 14,000 feet (5,000-10,000 psi).
Proppant pellets having a specific gravity of less than 3.4 g/cm3 have been made from diaspore clay, bauxite, and/or alumina. Eufala bauxite, a bauxitic-kaolin material, has been used to prepare a proppant with a density of less than 3.0 g/cm3. Also known is a method of making ceramic microspheres for use as proppants from water-soluble salts, mineral compositions or organometallic complexes, and ultrafine bauxite or alumina-containing particles. A low density proppant has been prepared from kaolin clay and amorphous to microcrystalline silica. The raw materials used to make all these intermediate proppants are costly, and a less expensive proppant material is desired.
Resin coated particles have been used in efforts to improve the stability of proppants at high closure stresses. Sand or other substrates have been coated with an infusible resin such as an epoxy or phenolic resin. These materials are superior to sand at intermediate stress levels. However, at high temperature and high stress levels, the resin coated particles still show a decrease in permeability.
A process is known for coating particulates with an infusible resin for use as proppants in fracturing operations. The particulates include sand, nut shells, glass beads and aluminum pellets. The resins include urea-aldehyde resins, phenol-aldehyde resins, epoxy resins, furfuryl alcohol resins and polyester or alkyd resins. The resin coating may be applied by mixing the particles with a melted resin and subsequently cooling the mixture, or dissolving the resin in a solvent, applying it to the particles, and evaporating the solvent. Coupling agents may be added to the system to improve the strength of the resin-substrate bond.
Proppants comprising sand particles with a precured phenol formaldehyde resin coating have been used for propping fractures in subterranean formations.
Although resin coated sands have proven satisfactory in numerous applications, concern exists over their use under high closure stresses. For example, some self consolidating resin coated particles of the prior art do not develop their full strength until the resin coating has cured in the formation. In the event of rapid closure of the fracture, the proppant could be crushed before the resin cured, resulting in decreased permeability. This problem is alleviated by the use of a dual resin coated particle having a reinforcing agent interspersed at the inner resin/outer resin boundary, as described in U.S. Pat. No. 5,422,183 assigned to Santrol, Inc, incorporated herein by reference as if fully written out below.
The present invention utilizes spent ceramic media from petroleum refining operations, where the media provides a catalytic function during xe2x80x9ccrackingxe2x80x9d of the hydrocarbons, while drawing out impurities from the crude oil as it passes through a packed column of ceramic beads. These beads are manufactured by Englehard Corporation, W R Grace and Akzo Nobel as well as other Far Eastern producers and are variously known as fluid cracking catalyst, e-cats, and equilibrium catalyst (hereinafter referred to as xe2x80x9cfluid cracking catalystxe2x80x9d or xe2x80x9cFCCxe2x80x9d). The use of catalytic ceramic media for removing impurities from petroleum products is a long established art. The catalytic media can be regenerated after use as a cracking catalyst several times but eventually is spent, and is discarded as waste material. The present invention uses the FCC as a base material for remanufacturing larger ceramic spheres, which can be used in the hydraulic fracturing of subterranean oil and gas bearing formations.
The present invention provides a spherical ceramic proppant pellet comprising spent fluid cracking catalyst particles, wherein the pellet is formed by reducing the median particle size of the catalyst; mixing the catalyst particles with water and a binder to form spherical pellets; and sintering the pellets.
The present invention also provides a method for preparing a spherical ceramic proppant pellet, the method comprising the steps of providing spent fluid cracking catalyst particles; reducing the particle size of the catalyst particles; mixing the catalyst particles with water and a binder to form spherical pellets; and sintering the pellets.
The present invention further provides a proppant composition comprising spent fluid cracking catalyst, wherein the spent fluid cracking catalyst comprises from about 25 to about 80 weight percent synthetic silica, and from about 20 to about 75 weight percent alumina. The spent fluid cracking catalyst may optionally further comprise at least one of:
up to about 1,000 parts per million copper;
up to about 7,000 parts per million vanadium;
up to about 200 parts per million lead;
up to about 7000 parts per million nickel;
up to about 2500 parts per million antimony;
up to about 2 weight percent iron;
up to about 1.5 weight percent sodium; and, detectable amounts of a least one component selected from the group consisting of platinum, rhenium, sulfur compounds, and rare earth metals.