Treatment of calcium-containing bentonites for drilling fluids

A method of preparing a treated bentonite mixture, the method comprising the steps of:

• a) mixing calcium bentonite and an aqueous mixture containing soda ash to form a first bentonite mixture, wherein the calcium bentonite contains 64 weight percent (wt %) of sodium montmorillonite, 3 wt % of illite, 9 wt % of kaolinite, 21 wt % of quartz, 1 wt % of calcite and 2 wt % of hematite;
• then
• b) adding starch to the first bentonite mixture to form a second bentonite mixture;
• and then
• c) adding sodium hydroxide to the second bentonite mixture such that the pH is adjusted to a pH greater than 10 to form a treated bentonite mixture.

A method of preparing a treated bentonite mixture, the method comprising the steps of:

• a) mixing calcium bentonite and an aqueous mixture containing soda ash to form a first bentonite mixture, wherein the calcium bentonite contains 56 weight percent (wt %) of sodium montmorillonite, 4 wt % of illite, 8 wt % of kaolinite, 21 wt % of quartz, 2 wt % of albite and 9 wt % of hematite;
• then
• b) adding starch to the first bentonite mixture to form a second bentonite mixture;
• and then
• c) adding sodium hydroxide to the second bentonite mixture such that the pH is adjusted to a pH greater than 10 to form a treated bentonite mixture.