Effect of temperature and extended static time on rheological properties of drilling fluids

The drilling industry has faced a lot of problems due to the poor conditioning of drilling fluids at bottom-hole conditions thus, drilling fluid properties change owing to an elevated temperature and also the properties deteriorate under static conditions hence, affecting drilling operations. However, these problems may lead to non-productive time (NPT) thereby, increasing the cost of operation and it may lead to a kick or blow-out. Attention must be given to a proper selection of drilling fluid as well as effective performance of the rheological properties. To make up for this gap, effect of rheological properties behaviour of pseudo-oil and water based drilling fluids were investigated at different temperatures and static time. Test results indicated high viscosity readings, yield point and gel strength of the pseudo-oil and water based drilling fluids decreased significantly with increasing temperatures of 800F, 1200F, 1500F and 1900F respectively whereas the parameters increased at a given temperature with an increase in extended static time. Conversely, there was a clear reduction in plastic viscosities with an increase in extended static time for every temperature that was considered. Models were developed for different shear rate for both the water base mud and the oil based mud, the goodness of fit for the water and pseudo-oil base mud. It was observed that the water base mud model for all shear rate gave better R2 and Adjusted R2 value, this indicates that the water based model will give a better result when used for prediction than the pseudo-oil base model. From the results obtained, no doubt, having good understanding of the rheological behaviour of a drilling fluid at down-hole conditions and static time will mitigatea lot of drilling problems if the optimum values of these rheological properties are monitored and maintained in drilling operations.