Assessment of Dynamic Filtration Formation Damage for Alaskan North Slope Drilling Fluids

Abstract

Abstract The recent drive towards open hole completions and highly deviated or horizontal wells in the Alaskan North Slope has emphasized the need for evaluating drilling or completion fluids suitability from a perspective of formation damage. A significant decrease in well productivity near the wellbore can occur due to the invasion of fine solids from drilling fluids, forming external and internal filter cake under dynamic conditions. The objective of this study was to evaluate formation damage caused by drilling fluids typically used for drilling gas hydrate zones. Alaska has vast reserves of gas hydrate, which is a source of energy with great potential for future development. Drilling through gas hydrates results in heat transfer into the formation, leading to dissociation of hydrates. Chilled drilling fluids and high circulation rates are commonly used to minimize this effect. An experimental setup for the evaluation of formation damage at in-situ conditions was designed. At the confining pressure of 1500 psi, chilled drilling fluids at 41-50°F are circulated across the Berea sandstone core for 10 hours in a dynamic filtration core holder. KCl/polymer water-based base mud, flocculated mud, flocculated mud with starch based filtration control material (Mackenzie Delta mud) and dispersed mud are tested at 30, 40, 80 sec−1 and 100/200 psi overbalance with absolute permeability measurement both before and after the drilling fluid circulation. The drilling fluid type, its flow rate, and shear rate, effective particle size, additive concentration, and the amount of static and dynamic overbalance were characterized to establish their influence on drilling mud leak-off volume and the post mud circulation permeability. The results showed that permeability impairment was strongly dependent on annular fluid velocity, amount of overbalance, mud salinity, and state of dispersion of the mud. Dynamic filtration showed significantly higher formation damage than static filtration.