Performance studies of water-based drilling fluid for drilling through hydrate bearing sediments

Hydrate-bearing formation is a highly unconsolidated formation and being fragile, the hydrates get readily decomposed while drilling through it. To successfully drill through the hydrates, the drilling fluid should have low mud invasion, exhibit optimum properties for wellbore stability, prevent the formation of the hydrates in the annulus, choke lines, etc. Initial experiments were performed with the drilling fluid with the composition as artificial seawater, 3.0 wt% bentonite, 3.0 wt% barite, and 0.3 wt% carboxymethyl cellulose (CMC) (wt%). The rheological, filtration and gelling properties were determined. The synergistic effects of xanthan gum (XG) and CMC with different compositions were used to study rheological properties. The drilling fluid with desirable rheological properties was further studied at low temperatures and at high pressures. The drilling fluid was tested for hydrate inhibiting properties in a high-pressure autoclave vessel at 16.55 MPa and at 0 degrees C and further tested with increasing water cut at both static and dynamic conditions. The experimental results reveal that XG has better viscosifying properties while CMC has a better filtration loss properties. With the increase in the concentration of the both CMC and XG, there has been an increase in viscosity, yield point, gel strength and decrease in the filtration loss. The experimental results also show that the developed drilling fluid has good inhibiting properties under static conditions but with an increase in water cut the risk of formation of hydrates increases.