Development of novel inhibitive water-based drilling muds for oil and gas field applications

Abstract

The aim of this study is to develop inhibitive drilling fluid systems generated from waste materials that can contribute to the reduction of potential well instability problems caused by drilling fluid based on rheological and filtration properties. In this study, a comprehensive experimental work was carried out to assess suitability of fly ash and rice husk ash, which are quite a large amount of waste, in inhibitive water based-drilling fluids at ambient temperature. To this end, inhibitive drilling fluids systems were formulated with various concentrations (0, 1, 3, 5, 7, 9, 12.5, 15 (wt%)) of fly ash and rice husk ash with 0, 2, 4, 7, 9, 12.5, 15 (wt%) concentrations in the two type of inhibitive drilling fluid systems and combined use of fly ash and rice husk ash with their optimum concentrations determined was analyzed in the inhibitive drilling fluid in order to determine the drilling fluid with the most favorable characteristics based on rheological and filtration properties including apparent viscosity (AV), plastic viscosity (PV), yield point (YP), gel strength, fluid loss and mud cake thickness. In addition, grinding impact of fly ash particles in the inhibitive drilling fluid system was determined in the development of the drilling fluid by employing mechanically ground fly ash for 30, 60 and 120 min in a tumbling ball mill. Finally, fly ash and rice husk ash were characterized based on X-Ray Fluorescence (XRF), X-Ray Diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR) and Scanning Electron Microscopy (SEM). Experimental results show that developed drilling fluids with fly ash and rice husk ash not only enhanced rheological properties but also improved the filtration properties by increasing the rheological parameters and decreasing fluid loss and mud cake thickness. With the developed drilling fluids, AV, YP and PV increased by 35%, 32%, 28%, respectively with fly ash for the 12.5 wt% concentration while the parameters increased by 19%, 27%, 14%, respectively with the 4 wt% rice husk ash. Gel strengths of the fluids slightly increased compared to reference fluid and were in acceptable range. On the other hand, developed drilling fluid resulted in a 10% and 12% reduction in fluid loss for fly ash and rice husk ash at 12.5 wt% and 4 wt% concentrations, respectively, as well as a 54% and 63% reduction in mud cake thickness. In addition, the results reveal that developed drilling fluid with sieved fly ash yielded superior flow behavior compared to drilling fluid formulated with ground forms of fly ash. Consequently, based on the study, non-damaging and inhibitive drilling fluid systems were developed by using waste material fly ash and rice husk ash, and hence enhancing performance of drilling operation as well as reducing the risk of amount of wastes disposed to the environment and the potential of issues such as formation damage, wellbore instability caused by drilling fluid and associated challenges.