In a well-known field in Southern Europe, the top-hole sections, characterized by highly fractured carbonate formation, the operator successfully and safely drilled two wells with an engineered viscoelastic water-based drilling fluid that highly contributed to minimize formation losses and reduce environmental impact across the surface aquifer. Operators historically drilled the shallow carbonate sections with gel polymer systems and conventional remedial treatments without acceptable results in solving this troublesome problem with a negative impact on non-productive time (NPT) and overall project cost. The use of a selected viscoelastic water-based drilling fluid system, with a thixotropic behaviour, and appropriate lost circulation procedures drastically reduced downhole loss rates and improved overall drilling performance. Laboratory testing conducted during the planning and execution phases of the project helped evaluate products compatibility and verify the effectiveness of the selected LCM in sealing the expected fractures. This unique system represents the first line of defence in the lost circulation mitigation strategy as it itself is an effective lost circulation control fluid system. In fact, due to its viscoelastics nature, it is able to develop a gel structure in void spaces when away from mechanical action in the wellbore. One advantage of this system is its simplicity being composed by only two key components to develop the thixotropic behaviour. The application of this fluid contributed to minimize formation losses and reduce products and water consumption. In addition to that, it shown excellent results in terms of hole cleaning efficiency while drilling large top hole sections due to its pseudo plastic behaviour.
Lost circulation is one of the common drilling challenge and a major concern in the oil and gas industry that could lead to detrimental effects such as large materials consumption, non-productive time (NPT), risk of stuck pipe and potential well control events. The inability to control downhole losses can result in increasing operation costs and potentially compromising safety, the environment and project economics1. Lost circulation prevention and mitigation starts with a comprehensive approach including the selection of the appropriate drilling fluid and LCM based on loss zone identification and characterization.
