Drilling problems in clay formations and drilling fluids

During oil exploration and production, instability of shales in drilled formations causes serious operational problems. Wellbore stability and formation efficiency depend on the selected drilling fluid type based on the interactions between formation chemistry and drilling mud. In this thesis, shale types, wellbore stability and drill pipe stucks are explained. The causes and mechanisms of wellbore instability and the techniques used to investigate clay minerals and shale sample characterization are discussed. Considerable improvements in fluid stability and rheology parameters have been observed, especially with the development of new drilling fluid additives, but the main problem today is to improve inhibition and filtration properties. The question of which are the main factors (sample quality, physical or chemical factors, experimental method used or clay mineral content) effecting these different results has been answered. In our country, especially in the Southeastern Anatolia Region, thick formations with active shales are cut before reaching the production zones. The problems such as tight holes, wellbore collapse and drill pipe stucks due to well stability cause significant financial losses and delays in drilling these formations. Well stability problems due to tectonic activity, which is particularly prominent in this region due to the interaction of active shales with water and changes in the mechanical properties of the rock, are frequently observed. Water-based, non-inhibitory bentonite-lignosulphonate muds are widely used for drilling in these formations due to their low cost and familiarity. However, in order to prevent stability problems, methods such as short trips applied at frequent intervals, without considering pore pressure and in-situ stresses and unplanned mud aggravation are used.