Screening and Evaluation of Some Environment-Friendly Mud Additives To Use in Water-Based Drilling Muds

Abstract

Abstract Environmental safeguard policies enacted by EPA, state and federal governments for effective management of onshore, offshore, coastal and other areas dictate the identification of environment friendly muds and mud additives. The increasing concerns of world communities to protect the global environment from the detrimental effect of oil-based muds dictate the use of environment friendly water-based muds. However, water-based muds with excellent environmental characteristics often become obsolete due to poor technical performance and low thermal stability. This paper describes the results of three novel mud additives to control the viscous, fluid loss and thermal stability of water-based muds. A comparative study of the viscosity generating characteristics of a newly identified viscosifier indicates better performance at the same concentration with respect to a widely used viscosifier. Several fluid loss additives, developed using an environment friendly technique, show better performance than a widely used fluid loss additive. A newly identified thermal degradation inhibitor improved the thermal stability of a bentonite mud up to 150 °C. Experimental data indicate more than 100% increase in PV, 400% increase in YP and 200% increase in 10 seconds gel strength for the base bentonite mud after hot rolling at 150 °C for 16 hours. However, this mud showed about 40% increase in PV and virtually no change in the YP and thixotropic property after hot rolling at 150 °C for 16 hours in the presence of the newly identified thermal degradation inhibitor. Introduction Drilling fluid is a complex system that contains a fluid phase, a solid phase and a chemical phase. Other than the fluid (either water or oil or both) and the solid phases, different types of chemicals and polymers are used in designing a drilling mud to meet some functional requirements such as appropriate mud rheology, density, mud activity, fluid loss control property etc (Amanullah et al. 1997). Though the factors that guide the choice of a fluid base and the mud additives are complex (Gray, 1980), the selection of the additives must take account of both the technical and environmental factors to eliminate any environmental impact (Amanullah, 1993). However, due to delayed realisation of the environmental impact of mud additives such as chemicals, polymers, salt water and oil-based fluids, little attention was paid in the consideration of environmental factors at the early stage of drilling. Moreover, the manifestation of the negative environmental impact of some additives after long period of slow and silent action made the realisation even difficult. Due to the detrimental effect of some mud additives such as potassium chloride, potassium sulphate, polyamine etc., the drilling and operating companies were forced to review their mud additive selection guidelines to exclude or control the use of non-environment friendly and low toxic mud additives in the formulation of water-based muds. Since some of the mud additives that were acceptable from environmental point of views decades ago, are not tolerable now-a-days, the industry is keen to avoid the same problem in the future. For this reason, the industry is dedicated to replace some of the low toxic, less harmful and less pure mud additives that are acceptable according to currents environmental norms but may not be tolerable in future due to the introduction of increasingly strict environmental legislations to protect the global environment. Moreover, some of the mud additives that are considered environment friendly on the basis of the evaluation of short term exposure effect may not be acceptable if they show long term exposure effect. This may lead to the changes in mud and mud additives selection and disposal guidelines all over the world. This is reflected by the change in the AEUB Guidelines (1996) for gel chemical mud systems by the introduction of new Interim Guidelines (2001) for advanced gel chemical wastes due to the realisation of the environmental impact of potassium sulphate containing water-based mud. Darlene Lintott et al. (2003) provide a detailed description of a potassium sulphate-based gel chemical system along with its disposal criteria in terrestrial ecosystems.