Improving the Environmental Impact of Drilling Fluids: Case History of a New, Salt-Free, Non-Aqueous Fluid

Abstract

Abstract Disposal of drill cuttings from non-aqueous drilling fluids (NAF) can be a significant expense and logistical issue for the operator of a drilling rig. NAFs typically contain high levels of salts, commonly calcium chloride or sodium chloride, in the internal phase of the emulsion. These salts are highly beneficial for wellbore-stabilization performance, but pose issues for the disposal of drill cuttings because the salts do not biodegrade and can accumulate in high concentrations in soil. A salt-free NAF has been developed and field validated in the Western Canadian Sedimentary Basin in Alberta, Canada. The system uses a biodegradable organic to provide an internal phase with equivalent water activity to traditional salt-containing systems. This results in a fluid system with the performance and benefits of a conventional NAF, while potentially allowing for greater cuttings disposal options. Depending on local regulations, the system has the potential to reduce environmental and long-term liability concerns by being able to land-farm drilled cuttings without hindering plant growth. Three wells on a seven-well pad were drilled with the salt-free NAF; the other four were drilled with a conventional invert emulsion fluid (IEF). Cuttings from one of each type of well were collected. A bioremediation study was conducted to analyze the cuttings for electrical conductivity and plant growth. Cuttings were delivered to the lab for testing and analysis. Laboratory testing showed that when mixed with top soil, the salt-free cuttings allowed for viable plant growth; whereas, the conventional cuttings did not allow for plant growth. This paper will discuss in detail the bioremediation study of the salt-free NAF. A salt-free NAF has been developed in the lab and successfully validated in the field. Cuttings from the salt-free system showed superior plant growth when compared to conventional, salt-containing systems. This system is expected to offer expanded options for cuttings disposal and, ultimately, reduce the cost and liability associated with using NAFs in many areas.