Case Study: Biological Treatment of Geothermal Drilling Cuttings

Abstract

This paper focuses on the bioremediation technology used for the mud and the drilling cuttings obtained during the drilling of five geothermal wells in the period between August 2007 and May 2008. Polaris Energy Nicaragua S.A. is developing the San Jacinto Tizate geothermal project near to Leon, Nicaragua. The first well drilled reached a depth of 150 meters, but was abandoned after a blowout at 150 m. The other four (reinjection and production) wells were drilled successfully without problems and reached depths of between 1000 and 2000 meters.
The geothermal well drilling process may negatively impact the environment, therefore it is necessary to introduce measures in order to prevent, control and mitigate the environmental impacts that they can produce. The mud and the drilling cuttings are a key environmental issue after the process of drilling a well. The biological treatment, also known as biotreatment or bioremediation, uses microorganisms like: bacteria and fungi to biologically degrade waste into nontoxic residues. The objective of biotreatment is to accelerate the natural decomposition process by adding: manures that contribute to the fertility of the waste, nutrients, aeration, moisture, and a small portion of soil.
Some advantages of biological treatment are: it is relatively environmentally benign; it generates few emissions; wastes are converted into useful products; and it requires minimal transportation. In this case bioremediation was used as a final disposal step and the waste was used for establishment and growth of vetiver grass for use elsewhere in the project as erosion control planting.