Review of Twente Salt Dissolution Studies
Résumé
NAM is currently producing the Schoonebeek Oilfield in the Netherlands and has to manage great amounts of production waters of low salinity. Reinjection into nearby depleted gas fields (a.o.Tubbergen, and Rossum Weerselo) was investigated and operations have started in 2011. The Dutch regulator, SodM, requested further studies complementary to the initial Environmental Impact Assessment to ensure that these reinjection activities are performed in a sustainable and socially responsible manner, the main concern being to assess the risk of degrading cap rock integrity through salt dissolution. These studies are detailed in three reports, namely refered to as [1], [2] and [3], dealing respectively with EP20130201845 “Geology description of Twente gas field”, EP20130203080 on “Halite dissolution modeling”, and EP20130204177 on “Subsidence caused by halite dissolution”. Complementary NAM technical reports have been analysed as background information for the scope of the reviewing process. We had therefore access to NAM documents, EP201502207168 on threat assessment for induced seismicity [4] and EP201410210164, on Technical evaluation of water injection wells, 3 years after start of injection [5]. A first round of complete evaluation of the project is planned for 2016 and multidisciplinary analysis of three NAM reports is underway. The present review of [1], [2] and[3] is a contribution to this evaluation, one major concern being the compatibility of massive fresh water with the evaporitic sequence forming the hosting reservoirs and the risk of loss of confinement that would translate at minima in groundwater quality issues. The three reports were at first separately evaluated.