Page:Niger Delta Ecosystems- the ERA Handbook, 1998.djvu/183

Environmental Impact of the Oil Industry

Drilling - Discharge of Muddy Drilling Fluid Waste in Drainage Systems

Although the Nigerian oil industry does not use chemical (oil based) drilling fluids, the discharge of the muddy drilling fluids (see section 3.4 of the previous chapter) into the neighbouring drainage systems is a serious problem, increasing turbidity and organic matter content often substantially increasing biological oxygen demand. These problems are particularly acute in mangrove environments and during the dry season when flushing rates are low. The 1995 World Bank report estimated that approximately 7 million m³ of drilling waste has been produced in the Niger Delta since oil prospecting began, an average bore hole giving rise to 2,500 m³.

Discharge of waste in the creek (mangrove) will increase the turbidity of the water and sedimentation of solids to the creek bottom and add (depending on the composition of the mud) organic matter, salts and chemicals to the host environment. The possible impact of increased turbidity and sedimentation is similar to the features described for dredging. The high organic matter content will lead to increased bacterial activity. .and could cause lower or even zero oxygen concentrations in parts of the creek, depending on the quantity of organic matter and the current velocity/dispersion rate. The discharge of waste with significantly higher or lower salinity or a different salt composition... than the receiving body could affect animal life. SPDC fact book of 1993

Drilling - Abandoned Well Linings

If the well proves to be dry, some well linings and cement plugs are left in the ground: see section 3.7 of the previous chapter.

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