Chloride-free Inhibitive Water-Based Fluid Significantly Improves Environmental Acceptability for Rain Forest Locations While Maintaining Drilling Performance
Authors: Dow Michael , Florence Angus , Babu JV 
Published: September 2012

While water-based fluids are generally preferred for drilling in environmentally sensitive locations, many are formulated with potassium chloride (KCl) to achieve good inhibition of reactive clays. The chloride ion however can be defined as a contaminant in land operations, with the potential to inhibit the growth of vegetation, and it can also be considered a potential pollutant to aquifers.

In the rain forest region of the Southern Highlands of Papua New Guinea (PNG), an alternative to the KCl high performance water based fluid (HPWBF) was needed to mitigate environmental concerns, affirm the operator's commitment to sustainable operations and provide continuous improvement as required by ISO 14001.

The fluid design team examined a range of alternatives and determined that potassium acetate (KAc) could replace KCl in the drilling fluid as a more environmentally acceptable inhibiting salt. Laboratory testing confirmed that the drilling performance properties of the fluid would not be impeded by substituting KAc for KCl. Experience using KAc fluids in other geographical areas was also examined to back up the laboratory testing.

The original KCl-based HPWBF had historically helped reduce issues related to the longer step-out wells, directional complexity, rock tectonics, and wellbore stability in the area. The new KAc system was used equally successfully to drill seven challenging wells. Both the technical and environmental objectives of the wells were achieved without sacrificing drilling performance. The change to KAc increased the fluid cost by approximately 10% when compared to the KCl-based system, but the operator concluded that this was a good investment, considering the distinct environmental benefits.

In a comprehensive review of the background to, and the successful implementation of the KAc HPWBF in to PNG Southern Highlands drilling, this paper firstly discusses the purposes of a drilling fluid. It will show how the presence of the potassium ion is regarded as essential within the drilling fluid, but the chloride ion has no discernible benefit. It considers the unique PNG Highland rainforest environment were the drilling operations occur, the local communities who live and interact with the operation, and how the operator has successfully protected this area. The drilling fluid disposal and discharge solutions in use in the Highlands operating area are discussed, how appropriate disposal solutions are selected, and how drilling fluid discharge is controlled to minimise any environmental impact.

In the second half of the paper, the methods used to develop the new chlorides-free KAc HPWBF system will be discussed. Results will then be presented from the seven wells drilled with KAc HPWBF, with two previous KCl wells used as reference. It will demonstrate that along with the improved environmental acceptance, drilling fluid robustness was maintained, as was on bottom drilling performance. Finally a review of material usage and costs indicates the change to the new KAc fluid did not have as significant an impact as first assumed, as KAc concentrations within the HPWBF were optimized.