HARD AND SALT WATER RESISTANT SELF SUSPENDING PROPPANTS
A self-suspending proppant comprises a proppant particle substrate and a coating on the proppant particle substrate comprising chitosan or a chitosan analog, wherein the coating has been applied to the proppant particle substrate of the proppant by means of an alkaline solution or emulsion.
1 . A self-suspending proppant comprising a proppant particle substrate and a coating on the proppant particle substrate comprising chitosan or a chitosan analog comprising another naturally occurring cationic polymer other than chitosan, wherein the coating has been applied to the proppant particle substrate of the proppant by means of an alkaline solution or emulsion.
2 . The self-suspending proppant of claim 1 , wherein coating comprises chitosan, and further wherein prior to application of the coating the proppant particle substrate has been treated with a silane coupling agent which includes a reactive functional group capable of reacting with the pendant amino groups on the chitosan molecule.
3 . The self-suspending proppant of claim 1 , wherein coating comprises a chitosan analog.
4 . The self-suspending proppant of claim 3 , wherein the chitosan analog is a cationic polysaccharide other than chitosan.
5 . The self-suspending proppant of claim 4 , wherein the chitosan analog is an unmodified starch or a modified starch selected from the group consisting of cationic starches, anionic starches, amphoteric starches, acid-modified starches, alkylated starches, oxidized starches and pre-gelatinized starches.
6 . The self-suspending proppant of claim 4 , wherein the chitosan analog is a cellulose or dextrin.
7 . The self-suspending proppant of claim 6 , wherein the cellulose or dextrin includes monosaccharide units having pendant hydroxyl groups and further wherein one or more pendant hydroxyl groups have been replaced by a functional group selected from the group consisting of amino, quaternary amino, ammonium, phosphonium, oxonium and sulfonium.
8 . The self-suspending proppant of claim 3 , wherein the chitosan analog has a pendant electronegative group, and further wherein prior to application of the coating the proppant particle substrate has been treated with a silane coupling agent which includes a reactive functional group capable of reacting with the pendant electronegative group of the chitosan analog molecule.
9 . The self-suspending proppant of claim 2 , wherein the self-suspending proppant is free-flowing when dry.
10 . The self-suspending proppant of claim 9 , wherein the self-suspending proppant is free-flowing after having been subjected to a relative humidity of between about 80%-90% for one hour at 25-35° C.
11 . The self-suspending proppant of claim 10 , wherein the self-suspending proppant remains self-suspending after having been subjected to shear at about 550 s −1 for 20 minutes.
12 . The self-suspending proppant of claim 2 , wherein the self-suspending proppant remains self-suspending after having been subjected to shear at about 550 s −1 for 20 minutes.
13 . A process for making a self-suspending proppant comprising a proppant particle substrate and a coating on the proppant particle substrate comprising chitosan or a chitosan analog comprising another naturally occurring cationic polymer other than chitosan, the process comprising coating the proppant particle substrate with an alkaline solution or emulsion of the chitosan or a chitosan analog and then drying the coated proppant so formed.
14 . The process of claim 13 , wherein prior to application of the coating the proppant particle substrate is treated with a silane coupling agent which includes a reactive functional group capable of reacting with the pendant amino groups on the chitosan molecule.
15 . The process of claim 13 , wherein coating comprises a chitosan analog.
16 . The process of claim 13 , wherein the chitosan analog is a cationic polysaccharide other than chitosan.
17 . The process of claim 16 , wherein the chitosan analog is an unmodified starch or a modified starch selected from the group consisting of cationic starches, anionic starches, amphoteric starches, acid-modified starches, alkylated starches, oxidized starches and pre-gelatinized starches.
18 . The process of claim 16 , wherein the chitosan analog is a cellulose or dextrin.
19 . The process of claim 18 , wherein the cellulose or dextrin includes monosaccharide units having pendant hydroxyl groups and further wherein one or more pendant hydroxyl groups have been replaced by a functional group selected from the group consisting of amino, quaternary amino, ammonium, phosphonium, oxonium and sulfonium.
20 . The process of claim 15 , wherein the chitosan analog has a pendant electronegative group, and further wherein prior to application of the coating the proppant particle substrate has been treated with a silane coupling agent which includes a reactive functional group capable of reacting with the pendant electronegative group of the chitosan analog molecule.
21 . An aqueous fracturing fluid comprising an aqueous carrier liquid and the self-suspending proppant of claim 1 .
22 . A method for fracturing a geological formation comprising pumping the fracturing fluid of claim 21 into the formation.