| Popis: |
An increasing number of wells are being drilled in formations with a high risk of well bore instability. Historically, the majority of instability was a result of drilling reactive clays with water-based fluids. This is still a common risk and is usually addressed by using oil- and synthetic-based fluids. However, we now more commonly have to overcome the problems associated with drilling depleted or weak formations which can be difficult to drill even with oil- or synthetic fluids. This is especially common in fields that have been producing for many years and where geological pressures have been altered. More and more often, stress caging techniques are being used to drill these unstable formations. Effective stress caging is relatively straight forward if all the parameters are known; however, this is rarely the case and accurate fracture and pore throat measurement in-situ is nearly impossible. To seal these fractures, which are sometimes a few microns or less, a new form of micro- or nano-sized sealant is required in addition to the conventional calcium carbonate/graphite particle blend. This paper presents a novel drilling fluid additive that utilises particles of approximately 200nm to seal fractures and pores to stop the invasion of drilling fluid filtrate and reduce pore pressure transmission. This enables wells to be drilled in depleted formations without losses, use very high overbalances with no differential sticking, and also plug micro pores and micro fractures found in shales to reduce instability and improve hole integrity. Laboratory testing is described that demonstrates the advantages of using this technology and case histories proving its usefulness in the field are described. Utilisation of this new nanotechnology will enable many problematic formations to be drilled safely and trouble-free by reducing the risk of wellbore failure. |
