Radioactive Marker Technique Applications to Evaluate Compaction in Environmentally Sensitive Areas

Radioactive Marker Technique (RMT) is a systems to evaluate layer compaction and land subsidence due to underground fluid production, based on the periodic monitoring of the distance between markers inserted into the formation, or onto casing. RMT is designed for the in situ measurement of the uniaxial compressibility coefficient (Cm) of layers under depletion, which is crucial to implement mathematical models to forecast compaction and its effects on the earth surface. After a brief description of measurement principles, the paper describes some aspects of RMT interpretation. A review of the main features of modern tools is given, weak points of measurement procedures and interpretation techniques are underlined and statistical methods utilized to reduce errors of Cm computation are presented. The paper addresses also a new subject of discussion, i.e., the effect of casing on the deformation of the surrounding layers, that are to be quantified in order to obtain more realistic measurements. Researches in this direction must be carried out, in the attempt to clarify some still vague aspects of interpretation techniques, and to assure reliable measurements and clear criteria of RMT applications. In general, RMT-derived Cm's match with sufficient precision with the ones derived from surface subsidence observed at surface, but not with the ones measured in laboratory. Finally, an application in Northern Adriatic Sea is presented, where RMT helped to improve the quality of lab-measured Cm's, allowing for a more precise environmental impact assessment of a possible hydrocarbon development project in a very sensitive area. At last, the well-studied case of Groningen gas field, and other offshore North Sea and Gulf of Mexico applications are reported.