Treatment of particles for improved performance as proppants
The disclosed invention relates to a process of using molten salt ion exchange to treat particles such as spherically shaped soda-lime-silica glass particles. The treated particles may be used as proppants in hydrofractured oil and natural gas wells.
1. A proppant having reduced generation of fines during failure comprising a particle selected from the group consisting of soda-lime-silica glass particles, glass-forming alumino silicate particles and mixtures thereof, the particle having a compressive stress state in the near surface region of the particle wherein the compressive stress state is formed by molten salt ion exchange between the particle and a molten salt selected from the group consisting of alkali salts, alkaline earth salts and mixtures thereof.
2. The proppant of claim 1 wherein the soda-lime-silica glass particles further comprise alkali oxides selected from the group consisting of Li 2 O and K 2 O and mixtures thereof.
3. The proppant of claim 2 wherein the particles have a spherical shape.
4. The proppant of claim 3 wherein the compressive stress state is maximum in the near surface region of the particles and lessens across a desired thickness of the particles.
5. The proppant of claim 1 wherein the alumino silicate particles are selected from the group consisting of andesite, rhyolite, basalt and mixtures thereof.
6. A pad composition comprising the proppant of claim 1 .
7. A method of producing particles suitable for use as a proppant having reduced generation of fines during failure comprising,
treating particles to a molten salt at an elevated temperature for a time period to cause molten salt ion exchange between the molten salt and the particles to impart a desired residual stress state in the near surface region of particles,
wherein the particles are selected from the group consisting of glass particles, glass-based particles and glass-forming aluminosilicate particles and wherein the salt is selected from the group consisting of alkali salts, alkaline earth salts and mixtures thereof.
8. The method of claim 7 wherein the glass particles are soda-lime-silica glass particles.
9. The method of claim 8 wherein the molten salt ion exchange is a single ion exchange and the particles are spherical.
10. The method of claim 9 wherein the salt is an alkaline earth salt selected from the group consisting of MgCl 2 , SrCl 2 , BaCl 2 , Be(NO 3 ) 2 , Mg(NO 3 ) 2 , Sr(NO 3 ) 2 , Ba(NO 3 ) 2 , BeCl 2 , and mixtures thereof.
11. The method of claim 9 wherein the salt is an alkali salt selected from group consisting of KCl, NaCl, KNO 3 , NaNO 3 , LiNO 3 and mixtures thereof.
12. The method of claim 9 wherein the temperature is about 350° C. to about 500° C.
13. The method of claim 7 wherein the molten salt is KNO 3 , the temperature is about 450° C. and the time period is about 7 hrs.
14. A method of producing particles suitable for use as a proppant having reduced generation of fines during failure comprising,
treating particles to a first molten salt at a first elevated temperature for a first time period to cause ion exchange between the molten salt and the particles to produce first exchanged particles having a desired residual stress state in the near surface region of the first exchanged particles wherein the particles are selected from the group consisting of glass particles, glass-based particles and glass-forming aluminosilicate particles, and
treating the first exchanged particles to a mixture of molten salts for a second time period to generate second exchanged particles that have a graded stress profile a across a given thickness of the particles.
15. The method of claim 14 wherein the glass particles are soda-lime-silica glass particles.
16. The method of claim 15 wherein the mixture of salts is selected from the group of mixtures of alkali salts, mixtures of alkaline earth salts and mixtures thereof.
17. The method of claim 16 wherein the alkali salts are selected from group consisting of KCl, NaCl, KNO 3 , NaNO 3 , LiNO 3 and mixtures thereof and the alkaline earth salts are selected from the group consisting of MgCl 2 , SrCl 2 , BaCl 2 , Be(NO 3 ) 2 , BeCl 2 , Mg(NO 3 ) 2 , Sr(NO 3 ) 2 , Ba(NO 3 ) 2 , and mixtures thereof.
18. The method of claim 16 wherein the mixtures of alkali salts are binary mixtures and the mixtures of alkaline earth salts are binary mixtures.
19. The method of claim 15 wherein the particles are spherical.
20. The method of claim 15 wherein the first molten salt is an alkali salt selected from group consisting of KCl, NaCl, KNO 3 , NaNO 3 , LiNO 3 and mixtures thereof.
21. The method of claim 14 wherein the second exchanged particles compressive stress is maximum in the near surface region of the particles and lessens across a given thickness of the particles.
22. The method of claim 14 wherein the first molten salt is KNO 3 , the first temperature is about 450° C., the first time period is about 7 hrs, the mixture of salts comprises KNO 3 and NaNO 3 , the second temperature is about 400° C. and the second time period is about 15 minutes.