STANDARD HANDBOOK OF PETROLEUM & NATURAL GAS ...

660 Drilling and Well Completions
Step 2. Knowing the weight percent of brine and using the volume percent of
freshwater by retort, the corrected volume fraction, which represents the true
volume percent of brine in the solution, can be determined by running a line
from the volume percent of water horizontally across until it meets the brine
concentration, then dropping vertically to find the true volume percent of brine in
the original mud. This number will always be greater than the volume percent
of freshwater by retort.
Volume fraction brine in internal phase:
Fvw = 20%
Weight % brine = 25%
Read 21.5% volume fraction brine in internal phase
Step 3. To determine the gravity solids in the drilling mud, it is necessary to
subtract from the mud weight all of the mud components except diesel oil and
low gravity solids.
To do so, subtract from the measured mud weight the fraction contributed
by brine and basic emulsifier (this step and Step 4). Knowing the volume fraction
of brine in the internal phase (from Step 2) and the weight percent of brine
(from Step l), follow the appropriate value for the volume of brine horizontally
to intersect the weight percent of brine. Extend that point vertically down to
determine the weight in lb/gal and subtract that weight from the mud weight
to correct for the weight of the internal phase.
Weight adjustment due to the internal phase:
Volume fraction of brine in internal phase = 21.5%
Weight percent of brine in internal phase = 25%
Read 0.69 lb/gal density adjustment
Step 4. This step corrects the mud weight and the volume percent of suspended
solids as a function of the hydrocarbons distilled off by the mud still.
Knowing the volume percent of oil from the mud still, follow this value vertically
until it meets the line representing the system being run. Then extend this
point horizontally to the left to determine the weight to subtract from the initial
mud weight.
Weight adjustment due to distilled hydrocarbons:
Volume % oil = 45%
Read 0.20 lb/gal specific weight adjustment
The initial mud weight less the sum of the weight adjustments from Steps 3
and 4 is the corrected mud weight representing the weight of the diesel oil,
low gravity solids, and barite only.
Calculation of adjusted mud weight:
Weight adjustment-internal phase = 0.69 lb/gal
Weight adjustment-emulsifier solids = 0.20 lb/gal
Mud weight = 15.7 lb/gal
Adjusted mud weight = 15.7 - 0.69 - 0.20 = 14.81 lb/gal