Note: Descriptions are shown in the official language in which they were submitted.
1~`22933
METHOD OF DETERMINATION OF WEIGHTING MATERIALS AND LOW
GRAVITY SOLIDS IN DRILLING FLUIDS
BACKGROUND OF THE INVENTION
This invention relates to new and useful improve-
ments in processes or methods of determining the amount of
solids of various kinds present in drilling fluids.
In order to impart the required density to drilling
fluids, weighting agents are added and although several
weighting agents can be used, the most widely used mate-
rial for this purpose is barite, which is a naturally
occurring barium sulphate (CHBr3). This barite is added to
the drilling fluid in the form of a very fine powder, which
is insoluble within the base of the drilling fluid. Che-
mically pure barium sulphate has a specific gravity of 4.50
but the grade of barite used in drilling fluids has usually
a specific gravity of approximately 4.2. Grades of barite
with a lower specific gravity are less desirable because
they contain larger amounts of impurities which may be de-
trimental to the drilling operations in various ways.
In deep hole drilling, barite costs form a large
part of the total cost of the drilling fluid materials and
since deep hole drilling is becoming increasingly necessary,
and good sources of barite are becoming scarce, a reliable
1222933
and simple method to determine the actual concentration of
the barite or other weighting material, present in drilling
fluids, is required.
At the present time, the concentration of barite
or other weighting material is calculated in an indirect
way, frum the amount of total solids as determined by re-
tort distillation to dryness. In this conventional retort
method, the amount of total solids follows from the amount
of liquid (water and oil) that is collected as distillate.
A material-balance equation, in which values for specific
gravity of "low gravity solids" (comprised of bentonite
or other viscosifying clays and drill solids and the like)
and "high gravity solids" (weighting materials such as ba-
rite) are assumed, thus allowing calculation of a value
for the concentration of the weighting material from the
total solids content and the density of the drilling fluid.
Utilizing these same data, the concentration of low gravi-
ty solids is also calculated from a similar material-balance
equation. It will be appreciated that these calculations
suffer from inherent inaccuracies of the retort procedure
inasmuch as the weighting material concentration is calcu-
lated in an indirect way, based on values which are not
known accurately.
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933
SUMMARY OF TH_ INVENTION
The present invention overcomes these disadvantages
and makes use of the fact that a weighting agent or material
has a specific gravity that is larger or higher than the
specific gravity of the low gravity solids, which is usually
approximately 2.5 and lower or below the specific gravity
of the high gravity solids consisting of the weighting
agents.
In accordance with the invention there is provided
a method for determining the amount of solids present in
drilling fluids, particularly relatively high gravity so-
lids used as weighting agents; consisting of the steps of
taking a sample of the drilling fluid, mixing same with a
quantity of a developer liquid having a specific gravity
lower than the specific gravity of the weighting agent and
being effectively non-immiscible with the base of the dril-
ling fluid and in which the weighting agent is insoluble,
then forcing the weighting agent out of the drilling fluid
and into the developer liquid, allowing the weighting agent
to settle by gravity and then determining the amount of
settled weighting agent.
The use of the method of the present invention
will therefore result in an accurate determination of the
actual concentration of the weighting agent or material
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present in the drilling fluids so that the necessary ad-
justments (if any) can be made readily and easily and with-
out wastage occurring of the weighting agent.
A further advantage of the present method is that
it is simple in operation, economical in use and otherwise
well suited to the purpose for which it is designed.
With the foregoing in view, and other advantages
as will become apparent to those skilled in the art to which
the invention relates as this specification proceeds, the
invention is herein described by reference to the accompany-
ing drawings forming a part hereof, which includes a des-
cription of the method of the principles of the present
invention, in which:
DESCRIPTION OF THE DRAWINGS
Figure 1 is a schematic view of a centrifuge tube
showing an example of the separation occurring by use of
the method.
Figure 2 is a representation of a graph showing
the preferred method of ascertaining the percentage of
weiyhting agents.
In the drawings like characters of reference in-
dicate corresponding parts in the different figures.
DETAILED DESCRIPTION
Before proceeding to describe the method in detail,
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933
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it will be noted that the examples utilized barite as a
weighting agent so that the developer is known as a
"barite developer". However, as will become apparent from
a reading of the specification and claims, other weighting
agents can be used and of course suitable developer li-
quids will be required.
As mentioned previously, the present invention
makes use of the fact that the weighting agents such as
barite or any practical weighting agent, has a specific
gravity that is larger than the gravity of the low gravity
solids which is usually approximately 2.5, and below or
lower than the specific gravity of the high gravity solids
consisting principally of the weighting agent used. The
low gravity solids normally consist of bentonite or other
clays which are added to the drilling fluids to provide
the necessary viscosity to same, together with drilled
solids which are obviously present in the drilling fluid
after some use.
Briefly, a sample of the drilling fluid is brought
into contact with a liquid called a weighting agent develop-
er, of a well defined composition with the specific gravity
of the developer being such that low gravity solids will
float on top of the liquid and that the high gravity solids
consisting primarily of the weighting agent, will sink in
1~22933
-- 6
the liquid. The high gravity solids or weighting agent
is thus separated conveniently from the o~her components
of the drilling fluid so that the amount of the weighting
agent can be determined.
It will be appreciated that the developer liquid
must satisfy the following specifications:
1. The liquid must have a specific gravity lar-
ger than that of the low gravity solids usually encoun-
tered in drilling fluids, so that its specific gravity
should be higher than approximately 2.5 up to approxima-
tely 3.0 or at least lower than the specific gravity of
the viscosifying clay utilized.
2. The developer liquid must have a specific
gravity lower than that of the weighting agent and if
this weighting agent is barite, it should be lower than
approximately 4.2. Needless to say, if other weighting
agents with different specific gravities are used, this
requirement must be changed accordingly.
3. The liquid should preferably not be miscible
with water in the case of water-based drilling fluids.
Miscibility with water will lead to a decrease of specific
gravity of the liquid by dilution with water from the
drilling fluid. This requirement can be circumvented by
ad3ustment of the relative amounts of drilling fluid sam-
, . . .
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-- 7
ple and weighted agent developer liquid used in the deter-
mination, or by increasing the specific gravity of the de-
veloper liquid above the limits set by the previous requi-
rements.
4. The developer liquid should preferably not be
miscible with oil in the case of oil-based drilling fluids
for similar reasons as mentioned in (3). However, this
requirement can be circumvented by similar measures.
5. The liquid should have miscibility properties
chosen in accordance with one of the two previous require-
ments in the case of emulsion-based drilling fluids con-
taining approximately equal amounts of water and oil.
6. The liquid should not dissolve the weighting
material present in the drilling fluid.
The majority of drilling fluids are water-based
and water-immiscible liquids that are suitable according
to the specifications required generally belong to the
class of halogenated organic compounds containing at least
two bromine or iodine atoms. Such organic compounds are
liquid and stable at between approximately 10C and 35C.
The example used in the present specification is
bromoform, (CHBr3), having a specific gravity of 2.89.
However, it will be appreciated that solutions of solids
w1th high specific gravity in organic solvents are not
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-- 8
excluded. Water-miscible liquids can be made from aqueous
solutions of salts of heavy metals such as thallium and
lead.
Because of the viscous nature of drilling fluids,
energy is needed to force the weighting agent out of the
fluid in which it is suspended, and thence into the deve-
loper liquid where it can settle. A convenient way of
effecting this separation is centrifugation of the test
mixture. It is advantageous to decrease the viscosity
of the drilling fluid by one or more of the following
techniques:
(a) dilution with water (or the relevant base
of the drilling fluid);
(b) addition of chemicals such as acids that
will decrease the viscosity and;
(c) oxidation of the organic polymers that are
often present in drilling fluids.
The actual determination of the amount of the
weighting agent can be accomplished most accurately by
removing the weighting agent that has settled in the
developer liquid phase and then drying same and weighing
the dried weighting agent. More conveniently, the volume
thereof can be read directly on a suitably graduated cen-
` ~ trifuge tube 10 in which the settling process has taken
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1222933
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place. By calibration with fluids containing known con-
centrations of the weighting agent, the volume readings
can be converted into concentration units by use of a
graph similar to that illustrated schematically in Figure
2 in which the base shows the percentage of the weighting
agent and the vert~ical,the volume with the necessary
reading being taken along the graph line.
An example of a procedure in which the above
principles are embodied is as follows:
A 2.5 ml sample of water-base drilling fluid was
placed in a l5 ml graduated centrifuge tube, such as that
shown schematically by reference character 10 in Figure 1.
To the sample was added ml of 3% hydrogen peroxide
and 1 ml of 0.2 M hydrochloric acid. The tube 10 was sha-
ken and heated in a hot water bath for approximately 15
minutes. After cooling to room temperature, lml of bromo-
form was added and the mixture was shaken.
The tube was then centrifuged at high speed in a
conventional centrifuge for five minutes and after centri-
fugation, the barite had settled to the bottom of the cen-
trifuge tube in the area identified 11 whereupon the volume
was read directly from the tube which was marked with the
necessary graduations (not illustrated). When one parti-
cular type of centrifuge was used, the factor to convert
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the volume (ml) of barite to concentration in the drilling
fluid (kg/m3) was found to be 777.
If the density, W, of the drilling fluid is known
in kg/m3, the amount of insoluble low gravity solids, LGS,
may be calculated in kg/m3 from the following formula:
LGS = 1.667 W - 1.296 B - 1667
Where B is concentration of barite (kg/m ) as de-
termined by the procedure forming a part of this invention
and described in the example above. If sodium chloride
and potassium chloride are also present, either alone or
together, the value of LGS must be decreased by the amount:
(2.675 x 10-4 K+ + 17. 716 x 10-4 Cl~)
Where K+ and Cl are the concentrations (mg/L) of
the potassium and chloride ions, respectively.
Since various modifications can be made in our in-
vention as hereinabove described, and many apparently wide-
ly different embodiments of same made within the spirit and
scope of the claims without departing from such spirit and
scope, it is intended that all matter contained in the ac-
companying specification shall be interpreted as illustra-
tive only and not in a limiting sense.
