Clay-free aqueous sea water drilling fluids containing magnesium oxide or calcium oxide as an additive

Claim 2

A CLAY FEED DRILLING FLUID COMPRISING AN AQUEOUS BRINE SOLUTION AND A SOLID ADDITIVE SYSTEM COMPRISING MAGNESIUM SULFATE AND DOLOMITE TOGETHER WITH AT LEAST ONE OF THE OXIDES OF MAGNESIUM AND CALCIUM AS A PROMOTER TO A REACTION TO INCREASE THE VESCOSITY OF THE FLUID SUFFICIENTLY TO ENABLE THE FLUID TO BE WEIGHTED TO A DENSITY OF FROM 12 TO 20 POUNDS PER BARREL.

Claim 3

The drilling fluid defined in claim 1 wherein said solid additive system is present in an amount of 5 to 175 pounds per barrel of brine solution and comprises about 30 to 70 percent by weight dolomite, about 20 to 60 percent by weight magnesium sulfate (measured as the heptahydrate form) and from about 3 to 10 percent by weight of at least one of the oxides of calcium and magnesium.

Claim 4

The drilling fluid defined in claim 1 wherein said brine solution comprises sea water containing additional dissolved salts in an amount of at least about 15 pounds per barrel.

Claim 5

The drilling fluid defined in claim 2 wherein said solid additive system is present in an amount of at least 40 pounds per barrel.

Claim 6

The drilling fluid defined in claim 4 wherein between about 2.5 and about 5.0 pounds of at least one oxide of calcium and magnesium is present in said solid additive system.

Claim 7

The drilling fluid defiend in claim 1 wherein the pH of the fluid is between about 8.5 and about 10.0.

Claim 8

The drilling fluid defined in claim 1 wherein said oxides of magnesium and calcium are present in the form of dolomitic quicklime.

Claim 9

The drilling fluid defined in claim 1 wherein said dolomite is dolomitic limestone.

Claim 10

The drilling fluid defined in claim 1 wherein said fluid includes starch in an amount of from about 10 to 20 pounds per barrel.

Claim 11

The drilling fluid of claim 9 wherein said starch comprises a mixture of 3 parts by weight pregelatinized corn starch to 1 part by weight tapioca flour.

Claim 12

The drilling fluid defined in claim 2 wherein said dolomite is dolomitic limestone containing at least about 35 percent by weight magnesium carbonate, said oxides are dolomitic quicklime, and said fluid has a pH of between about 8.5 and 9.5.

Claim 13

The drilling fluid defined in claim 2 wherein said solids additive system includes ground gypsum in an amount of from about 3 to 15 percent by weight.

Claim 14

The drilling fluid of claim 2 containing a weight material in an amount sufficient to provide a mud density of at least 12 pounds per barrel.

Claim 15

An acid soluble drilling fluid according to claim 13 wherein said weight material comprises finely ground ion oxide.

Claim 16

The drilling fluid of claim 2 wherein said brine solution contains, in addition to the components of said solid additive system, from 15 to 175 pounds per barrel of dissolved salts selected from the group of sodium chloride, potassium chloride, and magnesium chloride.

Claim 17

A clay free drilling fluid comprising from 5 to 175 pounds per barrel of a solid additive system containing 30 to 70 percent by weight dolomite, 20 to 60 percent by weight magnesium sulfate, 3 to 10 percent by weight of at least one of the oxides of calcium or magnesium, and 3 to 15 percent by weight gypsum; starch in an amount sufficient to provide desired fluid loss properties, said solid additive system being admixed in a brine solution containing 15 to 175 pounds per barrel of dissolved salts corresponding to salts anticipated in the formations to be drilled.

Claim 18

A clay free drilling fluid comprising from 5 to 175 pounds per barrel of a solid additive system containing 30 to 70 percent by weight dolomite, 20 to 60 percent by weight magnesium sulfate, 3 to 10 percent by weight of at least one of the oxides of calcium or magnesium, and 3 to 15 percent by weight gypsum; starch in an amount sufficient to provide desired fluid loss properties, said solid additive system being admixed in a brine solution containing 15 to 175 pounds per barrel of dissolved salts corresponding to salts anticipated in the formations to be drilled.

Claim 19

The drilling fluid of claim 16 wherein said oxides of calcium and magnesium are present in the form of dolomitic quicklime.

Claim 20

The drilling fluid of claim 16 including iron oxide as a weighting material.

Claim 21

The drilling fluid of claim 16 wherein said starch is a mixture of 3 parts by weight pregelatinized corn starch and 1 part by weight tapioca flour.

Claim 22

The drilling fluid of claim 16 wherein the salts in said brine solution comprise, in addition to the components of said additive system, potassium chloride and magnesium chloride.