Development of a Nanocomposite Gel for Lost Circulation Treatment

Abstract

Abstract The problems due to lost circulation events may represent a major source of expenses for drilling operators, even if their consequences do not have all the same level of gravity. Probably the most problematic situations are the naturally fractured formations where the operator may face total loss with no mud return in the annular. The voids or large fractures encountered in this case are often far too large to be plugged with conventional Lost Circulation Material. For these severe losses, the failure of extreme solutions as cement injection may even lead to loss of the well. Recently, treatments based on cross-linked pills have shown their effectiveness to plug large fractures under downhole conditions of pressure and temperature. This paper describes the research and development process to formulate a new cross-linked pill usable to control severe losses: this new pill is a nanocomposite organic/inorganic gel. Formulation strategy, laboratory procedures and experimental results will be described. The gelation time, the viscosity before setting, the gel strength formed and the dependence of these parameters with pressure, temperature and physico-chemical environment are characterized with specific experimental devices. Particular components of the formulation give excellent visco-elastic properties to the nanocomposite gel, enhancing the ability to sustain pressures peaks. The typical final formulation, which is easily prepared on site (dry blend formulation) gives remarkable properties regarding pumping through drill pipes, adjustment of setting time and especially strength of the lost zone sealing. Introduction During drilling operations, drilling fluids account for over 25–40% of total costs. Therefore, any mud loss increases the total cost and contributes to non-productive time of drilling jobs. Lost circulation or lost returns is defined as partial or total loss of circulating mud within the annulus escaping into formations.[1] Losses can result from either natural or induced causes.[2] Natural thief formations could be cavernous, fissured or coarsely permeable layers. Lost circulation is one of the drilling's biggest expenses in terms of rig time and safety. Moreover, uncontrolled lost circulation can result in a dangerous pressure control situation and loss of the well. So, in order to save money and to guarantee safe drilling jobs, several operators asked for new efficient solutions to reduce or eliminate lost circulation issues. The objective of this project was to develop new solutions to seal loss zones responsible of severe lost circulations due to, for example, naturally fractured formations. In this case, losses can range from tens of barrels per hour to thousand of barrels per hours. The developed remedial solutions are settable plugs that are polymer-based fluids that gel to seal off loss zones.