Optimization of glycol–water-based drilling fluid for drilling slim-hole wells in one of Iranian central oil fields

Slim-hole drilling has been widely developed in oil and gas industry. Frequent kicks, circulation loss, borehole wall destabilization, difficulty in cutting carrying, and stuck pipes due to the high-pressure difference existing in Dashtak formations are problems encountered in slim-hole drilling in this gas field. One of the major concerns while performing the slim-hole drilling operation is the drilling fluid hydraulics. Glycol–water-based fluid (GWBF) is a suitable alternative and received an increasing attention thanks to its optimum properties, including its easy preparation, low price, environmental friendliness, and high lubricity. In the current research, a total of 47 different samples of drilling fluids were evaluated with respect to their rheological properties. These fluids were studied through three different configurations for their calculate annular pressure loss (APL) gradients. The rheological properties of drilling fluids were assessed and compared using the power law (PL) and Bingham plastic (BP) models. Moreover, it was also attempted to investigate the impact of high temperature (180 °F) on APL. From the results of this study, it can be pointed out that the optimized GWBF has more stable rheology than water-based drilling fluids (WBDF) at 180 °F. The effect of high temperature was shown to be positive on the behavior of drilling fluids. However, it was found that high temperature affects the PL fluids more than the BP fluids.