The purpose of this report was to examine the fluid sensitivity of the rock samples from a particular well in the Colony Wash for an operator. The objective of the study was to compare oil base mud (OBM) and the Clear Fluid water base mud (WBM) samples provided by Mud Masters Group. (Click on the slides for a larger view.)

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The roller oven shale stability test simulates the circulation effect of the completion fluid around ground rock particles over a period of 16-24 hours at a desired temperature and studies the reduction of particle size due to mechanical attrition and reaction of shale particles with the reacting fluids.

In the modified API RP 13i procedure used in these studies, the shale is ground to a particle size less than 2 mm (10 mesh) and larger than 0.425 mm (40 mesh). These particles are split equally using a spinning Riffler then distributed equally into 10 gm samples. The number of samples depends on the number of fluids to be tested. The weighed sample is placed in a glass bottle along with 50 ml of fluid and allowed to roll in a roller oven at a desired temperature. Following the aging, the samples are screened through 70 mesh screen (0.269 mm) and washed with fresh water prior to drying and reweighing. The amount of sample pass through the 70 mesh screen is the measure of instability of the shale. The higher the percentage of solids passed through the 70 mesh screen, the lesser is the stability of the shale in that particular fluid.

The mass of sample passed through 70 mesh screen (0.269 mm) is expressed as a mass fraction in percent,

MP = (MI – MF)/MI *100

MP = Mass of shale passed through 70 mesh screen

MI = Initial mass of shale sample

MF = Final dry mass of shale sample

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Both samples demonstrated a high shale instability with 7% KCl and fresh water. A significantly higher instability was observed with fresh water relative to brine and both muds. A low to moderate instability was observed with the Nomac #15, indicating some encapsulation. The Mud Masters Clear Fluid mud on the other hand, indicated substantial encapsulation resulting in a weight gain for both samples. The samples were cleaned thoroughly with water and again with hexane but were still significantly coated, resulting in the weight gain. The tendency for erosion with diesel was low to moderate.


0-2 = Low Shale Instability

2-4 = Moderate Shale Instability

4+ = High Shale Instability