Abandoned wells and radioactive materials
A drilling operation is planned and designed in such a manner as to meet the objectives of the campaign safely, economically and in an environmentally friendly mode. The major objective here is to hit oil and in some cases to explore a regional field in order to have a better knowledge of the promises, certainties and uncertainties locked beneath the sub-surface. Sometimes, there could be surprises!
When drilling highly deviated and horizontal wells in depleted fields, there are many factors that can contribute to the possibility of a stuck pipe. The bottom hole assembly, BHA often includes a logging while drilling tool with radioactive sources for measuring formation porosity and density.
With the Azimuthal Density Neutron, ADN tool, it is possible to retrieve the radioactive source from within the tool when the tool becomes stuck in the wellbore. This is the most economic and environmentally friendly method of dealing with radioactive sources inside a stuck bottom hole assembly. In the Statfjord field in Norway, radioactive sources were retrieved from ADN tools stuck in three wells. One source was retrieved with coiled tubing while the other two were retrieved with electric wireline.
While drilling a well, it may collapse on the drill string, particularly, on the BHA for reasons of well instability arising from pressure differentials. The pressure imbalance could be as a result of sub-standard drilling mud, inadequate mud weight etc. but the key thing is that the well gives signs before striking.
Sometimes, the team is too busy not to notice or gauges installed to keep tabs on the indicators are not working properly. When the well collapses on the drill string, a quick intervention plan is immediately put in place to rescue the well and the drill string. Sometimes, the driller is lucky, sometimes he isn’t. Sometimes, there could be a well blowout and in both cases, the well is abandoned with tools buried in it. Most of these tool burials, radioactive inclusive, happen several thousand feet below the sea level. Offshore and onshore, Nigeria and globally, it is a standard operating problem. What may not be standard is the unsafe and environmentally unfriendly manner in which issues like these are handled by some operators.
According to the Journal of Environmental Sciences (Volume 3, No 10) of 2013, the average number of radioactive sources abandoned in oil wells in Nigeria between 2001 and 2007 is greater than the worldwide average. Most of these radioactive sources are high risk with considerably long half-lives which can pose dangers to human health and the environment. The nature of the containment as well as the location of the abandonment is such that, radioactive release to the environment could occur after a period of time thereby contaminating the environment.
Worldwide data on abandoned radioactive sources were available for 18 years. Data on loss of control of radioactive sources in oil wells which pose the threat of actual or potential release of radioactive materials to the environment were obtained from the International Atomic Energy Agency, IAEA. There is no data on stuck or abandonment of radioactive sources in oil wells in Nigeria prior to 2001.
Since 2001, there has been, at least one recorded case of abandonment of radioactive sources in oil wells in Nigeria. The highest number of reported cases was obtained in 2006 and this called for concern by both the well owners and the regulating authorities. Among the radioactive sources abandoned in Nigeria (2001 – 2007), there were 17 Cs-137 (30 years) and 17 Am-Be (433 years).
Therefore, the number of incidents recorded in Nigeria in the period under review is greater than the worldwide average. The annual risk rate (8.141 x 10-9 cancer deaths yearly) from abandoned logging sources in oil wells is slightly higher than the annual risk rate (3.695 x 10-9 cancer deaths per year) from low level waste repository. The reason being the site of low level waste repository is carefully selected and sufficient engineered barriers are put in place to shield the hemisphere from the effects of waste. The possibility of damaging the encapsulation of abandoned sealed source through human intrusion and natural disruptive processes could be high. This could lead to the release of radionuclides into the environment. However, the safety of the abandoned sources can be assured if dispersion of the radionuclide into the biosphere is driven by natural processes, is retarded until they have decayed to a safe level and if human intrusion into the source is unlikely.
It is gratifying that the frequency of such occurrences have plummeted, the world over, for reasons of technological innovations. The constitution of the Federal Republic of Nigeria in Section 20, states: “The state shall protect and improve the environment and safeguard the water, air and land, forest and wildlife of Nigeria.”
How far we have gone in this regard is another matter entirely! Perhaps, the law needs an amendment. Perhaps, agencies vested with this responsibility like the Directorate of Petroleum Resources, the Ministry of Environment and the Nigerian Nuclear Regulation Agency needs to reassure Nigerians in this regard. Perhaps, the Nigerian National Petroleum Corporation, as part of the reforms programed for the industry, needs to factor this into consideration. Let’s protect and preserve our environment by abandoning our wells responsibly. We have no other!
. Adeoye is an energy expert in Lagos.