Defining the optimum sequence in addition of shale inhibitor agents in WBDF considering inhibition of swelling of cuttings

Abstract

• We proposed and optimized sequence addition of shale inhibitive agents to WBDF. • Inhibitive behavior of WBDF classified to low, med and high, based on performance. • We have shown shale inhibitor agents should be added before rheological additives • Asphasol and polyglycol better to be added as late additives in low temperature WBDF. • PHPA, bentonite should be added before KCl, PAC and XC polymer in mud preparation. Shale swelling inhibition property in water-based drilling fluid (WBDF) is an important issue in drilling fluid engineering. Against the importance of chemical compounds used to give this property to the drilling fluid, sequence of adding those additives is also much of concern. In the presented study, we propose an optimized sequence of additives in the formulation of a standard WBDF. In the formulation, potassium chloride (KCl), partially hydrolyzed polyacrylamide polymer (PHPA), and polyglycol are used as major shale inhibitors. Therefor, 23 drilling fluid samples with variation in sequences of adding additives were experimented. Then 16 different WBDF samples were produced through changing the position of KCl, PHPA, bentonite and polyglycol and more 6 drilling fluids were prepared by simultaneous change in the position of PHPA, bentonite and KCl. Also, one oil-based drilling fluid (OBDF) was also produced and experimented against shale inhibition for performance comparison. Analyzing of swelling curves of all these drilling fluids revealed three different behaviors of them in shale inhibition. Then after, the optimized sequence of adding the shale inhibitors was defined according to the best observed performance of all experimented fluids. It should be noted that the presented study only focuses on the inhibition of swelling of cuttings and not on the dispersion of cuttings.