Víctor Jiménez Cubero
1st October 2012. A small 4.2 magnitude and 3rd degree on the EMS intensity scale earthquake produced social alarm among the inhabitants of the coastal cities of Tarragona and Castellón, but its origin was not caused by the usual seismicity of the area. Instead of this, was due to an enormous plan that was being developed off the coast of that region. We are referring to the largest gas injection project in the subsoil that has occurred in our country, thousands of meters deep, under the seabed, which came to be known as Castor Project.
This became famous not only because of the importance of the work, which pretended to store 1.9 billion cubic meters of gas, it was also because of the impacts derived from the injection and the hunch of had followed a poor environmental evaluation process in the project.
For our first contact with the topic, I will say that Castor Project, approved in 2008, was the last and largest of the 5 gas storage projects in the Spanish subsoil. It was raised with the reason of store up gas (Spain has a huge dependence on foreign energy resources) and make use of it in consumption peaks or during difficulties in purchasing it abroad. The old Amposta oil storage, on the coast of Vinaroz (Eastern Spain), would be used to inject gas from the net of gas pipelines to the old offshore platform (21km off the coast) and blow it to 1,750m depth. The porous nature of the limestones that once hold the oil bag enables the storage.
Image 1. Offshore platform off the coast of Vinaroz. (Source: https://elpais.com/)
The filling method was devised so that the gas injection displaced the water and then, filled the pores of the limestone substrata. These would be fulfilled with gas and would be perfectly sealed by the presence of a waterproof layer on the top. If necessary, and by filling the storage with water again, the gas could be recovered. It was an ambitious project, which promised to provide emergency resources to Spain. However, the problems started at 2012, as early as the first injection phase occurred.
Image 2. General diagram of facilities. (Source: https://geologicas.ucm.es/)
Considering the impacts derived from the project, since the mentioned start of filling in 2012, and until the following year, there were more than 500 earthquakes. Although this phenomenon was foreseen, it was not the fact that they appeared in a perceptible magnitude (micro-earthquakes of magnitude 1 were expected, at most 2). Subsequent reports from the NGI, in 2014, revealed the direct relationship between the filling and the increasing of shake frequency in the area. They also disclosed the existence of a fault, apart from Amposta one, not mapped at this time (it was named as Castor fault). This new crack was not considered at all in the project and the reports also ensured that the document of impact due to induced seismicity was not considered at all to rate the potential damage caused and the danger of the project.
After the increase in citizen unrest, the costs, raised to almost triple the initial forecast (from 600 to 1.700 billion €), the plunge in gas consumption and the NGI recommendations, the activities were permanently stopped in the platform, which had been inactive since a year before, when the first problems occurred during the injection of the named as “bed gas”. The fear of reactivating the fault dissuaded further attempts to extract the stored gas.
The conclusions are that the gas project, unsuccessfully executed from the political and technical point of view, brought with it an important repercussion in terms of costs for the state budget, since one of the companies involved had to be compensated due to the project sudden suspension (as agreed in the concession) and meant an output for a project that was never completed. Years later, it was described as “fanciful and unnecessary”. Furthermore, a good environmental monitoring surveillance could have prevented the worst quakes, because the gas was not being injected at the recommended pressure. Maybe this triggered it. In addition, it should be added that if the geological study had been done rigorously, the fault would have been located. If it did not yet exist at this time, it means that it was opened during the start of the works, so it was a negative, direct, irreversible and unforeseen impact, for which no one measure was considered.
Finally, the aim of this post is not to reprove the project management, but it is interesting for the Civil Engineering and Environment subject. That is a clear example of the drawbacks that a project brings if it does not deal with the study of environmental impacts. Zero alternative, for this specific case, would have been more favorable and it is possible that, if they have known it, the injections would never have started.