One environmental issue that has continued to receive increasing and significant attention in the Nigerian Oil and Gas Industry over the past decade is the management of drilling fluids and control of the disposal of the associated cuttings in the different ecological zones where exploratory activities take place. The development of theframework for the relevant regulatory control criteria have been based on scientific understanding of the potential environmental impacts and consideration for the sensitivities of the communities of the host regions.
The tortuous process of selection and approval of drilling fluids for each ecological zone and the respective set limits are described against the backdrop of available waste treatment technologies. This paper also reveals the peculiarities of the evolving concepts of development of regulations based on science, experiences of the international industry and local social issues as a means ofstriking an acceptable though delicate balance among stakeholders in drilling waste management.
The constraints in effective implementation of such policies within the economic bounds that characterize a mono product developing economy (as Nigeria) are discussed.
Introduction
Issues about regulations governing the handling and use of drilling fluids, and the disposal of associated cuttings have been very topical in the oil and gas industry in Nigeria since the beginning of the past decade. This has been so because of a number of factors. Whereas the operator understands that success in the process of drilling a hole through the earth's crust depends significantly on the performance of the drilling fluids and hence has his focus on striking a balance between cost and performance of the fluids, the regulator is concerned with ensuring that only environmentally friendly fluids are employed. There is therefore a conflict among stakeholders due to diverse interests in the management of drilling fluids and control of the disposal of associated cuttings, in Nigeria, especially as the oil bearing catchment zones, which make up the Niger Delta are "fragile" ecological zones. On their part, the host communities who live within these oil bearing zones, and have become rather sensitive to matters relating to environment and oil operations demand of the operators, very high levels of oil field practice.
Consequently, the regulatory agency, the Department of Petroleum Resources has responded to the contemporary issues and set up a process for the selection and approval of drilling fluids for use in different ecological zones. The process of approval for the discharge or disposal of waste fluids and/or associated cuttings constitute a well structured programme of environmental management especially as only available technology and conventional methods may be employed in the treatment and disposal of cuttings.
ENVIRONMENTAL SETTING IN THE NIGER DELTA
The Niger Delta is situated in the Gulf of Guinea on the West Coast of Central Africa and it built out into the Atlantic Ocean at the mouth of the Niger/Benue river system, covering a catchment that encompasses more than a million square meters. The entire Niger Delta is one of the world's largest, covering a total area of about 75,000 sq. km., and extending more than 300 km. from apex to mouth. The regressive wedge of eclastic sediment, which it comprises, is thought to reach a maximum thickness of about 12km. It is a plain, built up by accumulation of marine sediments, which has prograded southwards into oceanic crust, gradually assuming a convex-to-sea morphology. Throughout the geological history of the Niger Delta, the structure and stratigraphy have been controlled by the interplay between the rate of sediment supply and subsidence.
