On the uncertainties of monitoring subsidence from small sources: Dutch mining regulation on subsidence monitoring and its role in communication and accountability

摘要

Mining induced subsidence in the Netherlands is often associated with small gas fields (less than 5 km diameter), or discrete sources (converging salt caverns). As most of the areas experiencing this subsidence are close to sea level, and the effects of gas exploitation in Groningen may be considered a national trauma, there is strong emphasis on control and regulation of the related mining activities and their effects at the surface. The relatively small subsidence (often less than 10 cm), combined with inherent prediction uncertainty involving geological parameters, introduces a monitoring challenge to both mining companies and the regulator. A large initial uncertainty can be reduced during production by a carefully designed monitoring strategy, including evaluation of the results and clear communication on the effects on the uncertainty of the prognosis. In the same process, one may quantify remaining uncertainties and the limitations on predictability. In this contribution, we discuss the nature of some specific uncertainties associated with small source subsidence, and the effects on the regulatory process. The description is based on a realistic assessment of the expected accuracy of subsidence predictions. This allows for a clean comparison between different measurement techniques, and may help prevent overly optimistic claims on predictability. A description of uncertainty in terms of scenarios and parameter sensitivity studies should be used in communicating the expected level of subsidence control to water management boards and the general public.