Experimental and statistical investigation of drilling fluids loss in porous media–part 1

Abstract

Drilling fluids Invasion and mud filtration is a complex process that is influenced by several variables, and has NPT (Non-Productive Time) implications. Most of these variables are either within operational control limits (mud type, LCM type/concentration, and rotary speed) or pre-existing limits (temperature, fracture width, and rock type/permeability/porosity). It is unclear which of these variable(s) have significant positive or negative impact on dynamic fluid loss, filtration patterns, invasion rates, and plastering effect.The primary objective of the study presented in this paper is to quantify the contributing effects of temperature change, lost circulation material (LCM) type, concentration, size (particle size distribution), and variation in porous media on dynamic drilling fluids invasion. Statistical methods were used to determine the magnitude and significance of these independent variables. The fluid loss experiments reported herein were performed with a dynamic-radial system that accounts for rotary speed, eccentricity, torque, pressure, and temperature. The effects of the variables mentioned above were studied using ceramic filter tubes and thick-walled cylindrical limestone, sandstone, and chalk rock specimens.The results from the experiments showed that a change in temperature significantly affects fluid loss. The importance of rock mineralogy, porosity, and permeability in dictating dynamic fluid loss profiles, mud invasion rates, and plastering effects were also revealed by the fluid loss results. The results from the ceramic filter tubes, often undermines the effect of rock type which can be misleading. Statistical analyses showed no significant change in dynamic fluid loss with the two treatment levels of pore throat diameters that were investigated. These results cannot represent the actual porous media complexities. In the cases where vertical fractures were created and sealed, the combined effects of LCM and low permeability of rock specimen were defined in the reduced dynamic mud filtration results and filter cake plastering effects.