Risk Analysis Tool Applied to Understand the Possible Negative Environmental Effects of Unlined Drilling Pits in Desert Environments

摘要

Traditionally in desert operations in Libya, drilling mud and cuttings (water based) have been disposed of directly on the ground in unlined pits. This practice has lately been challenged because other than affecting the landscape, it can pose a risk to the soil and to shallow aquifers. To correctly assess the risk that this practice poses, REMSA and specialized environmental consultants developed a tool to predict the risk of pollutants transported by lixiviates reaching shallow aquifers below the drilling pit itself. The model has the capacity of determining the threat of a group of pollutants individually moving from the pit through the Unsaturated Zone. Other than modeling the movement driven by gravity, the model also considers biodegradation of organics and absorption processes within the Unsaturated Zone and dilution once in the Saturated Zone. This modeling tool (CREWD) has been tested in block NC186 in Libya and the results have been validated throughboreholes and excavations that reached down 4 meters below the bottom of the pit. The results obtained using the model, gave a clear indication that with the prevailing conditions in NC186 and knowing that the shallowest aquifer mapped is below 60 m depth, the risk of hydrocarbons, heavy metals or salts causing detrimental impact to the aquifer is extremely low.