Drilling practice with aerated drilling fluid : Indonesian and Icelandic geothermal fields

Abstract

Successful drilling is a key factor in developing geothermal fields. Drilling with aerated drilling fluid is an underbalanced drilling technique, mainly used to improve the production of wells and, in some cases, solve problems of borehole cleansing during the drilling operations. The aerated drilling technique consists of adding compressed air to the drilling fluid (mud or water). Aerated drilling fluid has a lower density than conventional drilling fluids, thus the hydrostatic pressure inside the well can be lower than the formation pressure. Using aerated drilling fluids makes it possible to reduce losses when encountering loss of circulation, which may block the formation through mud cake and decrease porosity and permeability by the infiltration of cuttings into the formation. With less formation damage, improved well production can be achieved. When drilling and using aerated drilling fluids, the annular pressure must be controlled in order to keep it underbalanced but the differential pressure must also be minimized in order to avoid too much gain that can cause a blow out. The density of aerated drilling fluids changes at depth as a result of variable temperature and annular pressure. Determination of the annular pressure when drilling with aerated drilling fluid is important when planning the drilling program and also important during the drilling operation to make adjustments that will maintain an underbalanced state and minimize the downhole differential pressure. The paper reviews the benefits of using aerated drilling ...