STANDARD HANDBOOK OF PETROLEUM & NATURAL GAS ...

Drilling Muds and Completion Fluids 661
Step 5. After having found the adjusted mud weight, proceed horizontally from
that point to the right to determine the volume percent of solids occupied by
the basic emulsifier package. The volume percent of suspended solids is 100%
less the sum of the volume-percent oil, the true volume-percent brine (Step 2),
and the volume-percent emulsifier solids.
Calculation of volume-percent suspended solids:
Volume % emulsifier solids = 1.03%
Volume fraction of brine = 21.5%
Volume % oil = 45%
Volume % suspended solids = 100 - 21.5 - 45 - 1.03 = 32.47%
Find the adjusted mud weight value, extend that point downward until it meets
the volume-percent suspended solids line. Proceed horizontally to find the ppg
of low gravity solids.
Calculation of low gravity solids, lb/bbl
Adjusted mud specific weight = 14.81 lb/gal
Volume % suspended solids = 32.47%
Read 90 lb/bbl low gravity solids
Step 6. To find the oil-to-water ratio, divide the volume percent of oil in the
liquid phase by (vo) by the volume percent of water in the liquid phase (vw).
Calculation of oil-water ratio:
v, = lOO[ -1 20 = 31%
45 + 20
69
Oiko-water ratio = -
31
Aging. The aging test is used to determine how the bottomhole conditions affect
oil-base mud properties. Aging cells were developed to aid in predicting the
performance of drilling mud under static, high-temperature conditions. If the
bottomhole temperature is greater than 212"F, the aging cells can be pressurized
with nitrogen, carbon dioxide, or air to a desired pressure to prevent boiling
and vaporization of the mud.
After aging period, three properties of the aged mud are determined before
the mud is agitated: shear strength, free oil, and solids settling. Shear strength
indicates whether the mud gels in the borehole. Second, the sample should be
observed to determine if free oil is present. Separation of free oil is a measure
of emulsion instability in the borehole, and is expressed in of an inch. Settling
of mud solids indicates formation of a hard or soft layer of sediment in the
borehole. After the unagitated sample has been examined, the usual tests for
determining rheological and filtration properties are performed.