Drying and gas or vapor contact with solids – Process – With contacting of material treated with solid or liquid agent
Reexamination Certificate
1999-12-01
2001-04-17
Gravini, Stephen (Department: 3749)
Drying and gas or vapor contact with solids
Process
With contacting of material treated with solid or liquid agent
C034S381000, C507S109000, C507S145000
Reexamination Certificate
active
06216361
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to drilling fluids and more particularly to the removal of water from oil based drilling fluids.
BACKGROUND OF THE INVENTION
When drilling boreholes through the earth, it is the normal practice to circulate a drilling fluid down the drill string, through the drill bit and then back up to the surface through the annulus between the drill string and the borehole wall. Drilling fluids perform a variety of functions and their characteristics, such as density, viscosity and chemical composition are carefully selected depending upon the functions to be performed, to avoid negative effects on the geological strata being penetrated and to maintain borehole integrity.
Continuous phase oil based drilling fluids are well known in the drilling industry and have been used successfully particularly when drilling through water sensitive formations such as certain types of clay-bearing shales that swell when contacted by fresh water. Ideally therefore, the drilling fluid should be maintained as a pure oil but in practice, water contamination of the oil is almost inevitable. Water can enter the system either from the surface (rain etc.) or, more typically, by ingress of formation water present in some of the strata penetrated by the bore. Typically, the drilling fluid is continuously monitored at the surface for water content using two tests, namely electrical stability to detect the physical presence of water if drilling with a non-viscosified pure oil, and/or distillation of a carefully measured sample of the fluid in a retort or still to determine the actual amount of water present in the fluid. Using the electrical stability test, if the fluid sample remains non-conductive up to an applied potential of 2000 volts, the fluid is considered to be water free. This test cannot however be used with a viscosified oil as the viscosifiers can emulsify the water and mask its presence. If the electrical potential at which the fluid becomes conductive drops below 2000 volts, or if a stability test is not possible and the presence of water is to be detected, the sample is placed in the retort and the free water is essentially boiled off and its volume is then compared to the volume of the oil itself which is boiled off at a higher temperature to separate it from any entrained solids in the sample.
If free water is detected, the usual practice has then been to attempt to neutralize the water by emulsifying it to form an internal discontinuous phase of small droplets within the oil based fluid. This is done by the addition of emulsifiers, surfactants and oil wetting agents to create an invert oil emulsion, as is well known in the art.
The presence of emulsified water in the oil still has negative effects, not the least of which can be excessive increases in the drilling fluid's viscosity that robs considerable efficiency from drilling operations. The water itself, particularly if fresh, is in ionic imbalance with usually saline formation water and must therefore be salinated, usually with calcium chloride (CaCl
2
). The presence of chloride ions in the drilling fluid adds considerably to the cost of treating and disposing of the drill cuttings.
In some instances, free water is added to an oil based drilling fluid deliberately. This might be done to raise the fluid's viscosity or to decrease filtrate loss to formation. Whether water is added deliberately or not, the drilling fluid must still be emulsified and salinated. The deliberate addition of water reflected the heretofore near inevitability of having to create an invert emulsion in any event. The present invention eliminates or at least reduces this inevitability and the characteristics sought to be obtained by the deliberate addition of water can now be obtained in other practical ways. For example, viscosity increases can be obtained by adding organophyllic clays. Fluid loss control can be regulated by the addition of, for example, gilsonite, calcium carbonate or cellulose fiber. If the fluid must be weighted up to offset formation pressures, additives such as barite can be introduced.
There are therefore considerable operation and cost advantages to drilling with a pure oil system and being able to avoid having to convert the system to an invert emulsion. The applicant has found that this is possible, or at least the conversion to an invert emulsion can be delayed, by scavenging the water from the drilling fluid on a continuous basis while drilling.
SUMMARY OF THE INVENTION
To scavenge the water from the drilling system, anhydrous magnesium sulfate is added to the drilling fluid. Water is removed according to the following chemical reaction:
MgSO
4
+7H
2
O→MgSO
4
·7H
2
O
Water reacts with the magnesium sulfate, precipitating magnesium sulfate heptahydrate, typically in balls or clumps.
Based on this reaction, and using the known molecular weights of MgSO
4
and water, it can be calculated that approximately one kilogram of magnesium sulfate is required to scavenge one liter of water. In practice, it has been found that an excess of up to approximately 50% of MgSO
4
is desirable for the reaction, which is exothermic, to go quickly to completion. Accordingly, approximately 1.50 kilograms of MgSO
4
are added to remove one liter of water.
According to the present invention, then, there is provided a method of removing water from oil-based drilling fluids used in the drilling of boreholes in the earth, comprising the step of adding MgSO
4
(magnesium sulfate) to said drilling fluid to remove the water therefrom.
According to a further aspect of the present invention there is also provided a method of removing free water from a hydrocarbon based drilling fluid used in the drilling of boreholes through the ground, comprising the steps of calculating the amount of water in the drilling fluid; and adding MgSO
4
(magnesium sulfate) to the drilling fluid to remove the water in accordance with the following formula: MgSO
4
+7H
2
O→MgSO
4
·7H
2
O, where: MgSO
4
is magnesium sulfate, H
2
O is water and MgSO
4
·7H
2
O is magnesium sulfate heptahydrate.
According to yet another aspect of the present invention, there is provided a method for testing for the presence of free water in a hydrocarbon based drilling fluid to which MgSO
4
(magnesium sulfate) has been added to scavenge water therefrom, comprising the steps of sampling a predetermined volume of said drilling fluid for heating in retort means; and elevating the temperature of said sample to a temperature above the boiling point of water and below the melting point of MgSO
4
·7H
2
O (magnesium sulfate heptahydrate) for a sufficient amount of time to boil off said water and collect the same.
According to yet another aspect of the present invention, there is provided a method of calculating the concentration of water in a hydrocarbon based drilling fluid to which MgSO
4
(magnesium sulfate) has been previously added to scavenge water therefrom, comprising the steps of collecting a predetermined volume of said drilling fluid for heating in retort means; elevating the temperature of said sample to a temperature above the boiling point of water and below the melting point of MgSO
4
·7H
2
O (magnesium sulfate heptahydrate) for a sufficient amount of time to boil off and collect said water; elevating the temperature of the remaining sample to above the boiling of said hydrocarbon based fluid and collecting any additionally released water and boiled off hydrocarbon; and calculating the concentration of said water in said drilling fluid by comparing the amount of boiled off water collected to the amount of boiled off hydrocarbon collected.
REFERENCES:
patent: 1701092 (1929-02-01), Zoul
patent: 2316967 (1943-04-01), Miller
patent: 2856154 (1958-10-01), Weiss et al.
patent: 3878110 (1975-04-01), Miller et al.
patent: 3979303 (1976-09-01), Kang et al.
patent: 4451377 (1984-05-01), Luxemburg
patent: 4888120 (1989-12-01), Mueller et al.
patent: 6076278 (2000-06-01), Bradley
patent: 2175859 (1997-11-01), None
Gray, George R. and Dar
Jeanson David Roger
Smith Richard J.
Gravini Stephen
Lerner David Littenberg Krumholz & Mentlik LLP
Newpark Canada Inc.
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