Experimental Study Of Potassium In Water-Based Mud (Wbm) For Shale Stability

Interest in designing Water-based Muds (WBM) have increased due to wellbore instability issues
that arise from the abundance of problematic shale encountered while drilling. Conventional
WBMs that are used to drill through sensitive shale formations cause a high degree of wellbore
instability. Thus, Oil-based Mud (OBM) were adopted to solve the wellbore instability problems
due to its superior shale stabilization properties. However, high costs, environmental restrictions,
cuttings and used mud disposal difficulties and safety have largely limited the use of OBM. As a
result of these challenges with OBMs, WBMs that have the ability to effectively reduce shale
instability problems have once again come under the lime light to replace the OBMs. Potassiumbased
(KCl) muds are used in areas where inhibition is required to limit chemical alteration of
shale. This research study therefore was undertaken to evaluate the inhibition effects of different
concentrations of KCl on the rheological properties of WBM contaminated with shale. The
rheological values using Fann viscometer with different concentrations of KCl (0.2%, 0.4%, 0.6%,
0.8% and 1.0%) respectively by weight of contaminated 8.7 ppg WBM with typical shale sample
from the shale outcrop at Batu Gajah, Perak (N04°28’25.8’’, E 101°4’26.9”) were evaluated. Test
results indicated that the KCl inhibited the swelling tendencies of the shale and the rheological
values reduced drastically. The reduction in rheological values considering the 600rpm reading
were 9.5%, 14.2%, 23.8%, 47.6% and 52.4% respectively compared to results without KCl in the
mud as indicated above. Therefore, to avoid non-productive time resulting from hole instability
problems caused by shale, when drilling is expected to encounter shale zones, proper design of the
drilling fluids using WBMs with KCl that will inhibit shale swelling is imperative.