EFFECT OF PRESSURE AND TEMPERATURE DISTRIBUTION TO THE DRILLING FLUID DENSITY FOR MANAGED PRESSURE DRILLING (MPD) APPLICATIONS

Drilling fluid performance is a major component that contributes to the drilling operations‟ success. This fluid is mainly used to promote borehole stability, removing drilled cuttings from borehole, cool and lubricate the bit and drill string, and to control the subsurface pressure. The effects of the temperature and pressure conditions prevalent in high temperature/high pressure wells with narrow operating windows on the equivalent circulating density (ECD) of drilling fluids in a circulating wellbore as well as the bottom-hole pressure are studied in this paper. High temperature conditions cause the fluid in the wellbore to expand, while high pressure conditions in deep wells cause fluid compression. Inappropriate consideration of these two opposing effects may result inaccurate estimation of bottom-hole pressure with incorrect application of Managed Pressure Drilling (MPD) techniques. The rheological properties of drilling fluids especially density of oil/synthetic based mud changes significantly in high pressure/temperature wells. This study was to determine the rheological properties of drilling fluids using empirical model from the experiments and simulated the ECD and bottom-hole circulating pressure with pressure and temperature as the main parameters. Paraffin based synthetic drilling fluid was used for this purpose and a simulator called Landmark® WellPlan was used to simulate the wellbore during circulation. A Bingham Plastic model was implemented to express the rheological behavior of the drilling fluid studied, with rheological properties expressed as functions of pressure and temperature. The applied backpressure, circulating times, and pump rates are used as variables in the simulation in order to simulate the ECD, bottom-hole circulating pressure and temperature profiles in the wellbore conditions. The results of the simulation show that higher pump rates lead to higher ECD and circulating pressure in the wellbore with higher pressure drop across the bit towards fracture gradient in the operating window. The circulating times for drilling fluids gives a significant effect on the ECD, circulating pressures, and temperature profile along the wellbore. The MPD application was simulated with the application of backpressure gives in higher ECD and circulating pressure at bottom-hole condition using optimum pump rate. The ECD and circulating pressure profile for paraffin synthetic based mud is strongly influenced by the effect of pressure and temperature during MPD applications.