Abstract The onset of hydrocarbon exploration and production activity in Spain dates back to 1860, mainly consisting of rudimentary mining of tar sands, asphalts and bituminous shales. Petroleum exploration drilling started properly in 1900 by simply locating wells in the vicinity of petroleum impregnations at the surface, often with little or no geological input. Until 1940, most of these early exploration wells were shallow tests (less than 500 m deep), commonly operated by small private companies with foreign investment, but no oil and gas accumulations were found. Systematic hydrocarbon exploration in Spain began in 1940 after the Spanish Civil War (1936–39). Two oil companies led these activities: CAMPSA, a state-run petroleum monopoly established in 1927; and CEPSA, a fully private Spanish company founded in 1929, which created the exploration subsidiary CIEPSA in 1940. However, the poor economic situation in Spain, the currency shortage and the international embargo after the Civil War made it very difficult to import any rig capable of deep drilling until the late 1940s. During the early 1950s, the domestic and international position of Spain started to improve. Slowly, foreign hydrocarbon exploration companies (especially German and American) began to form partnerships with national and Spanish private companies. They conducted the acquisition of the first seismic reflection surveys and were responsible for a considerable increase in deep drilling and pioneering borehole logging. Noteworthy amongst these were the intense activities of the VALDEBRO, a consortium formed in 1952 by American companies and the state. In 1960, 100 years after the initiation of petroleum production in Spain, the first commercial success was obtained with the discovery of dry gas in the Castillo-1 well, drilled by CIEPSA in the onshore Cantabrian–Basque Basin. This find was later complemented by the oil discovery at Ayoluengo in 1964 by a joint venture led by CAMPSA and which still remains the only commercial oil field discovered onshore Spain.

Preparation of these workshop lectures on the broad topic of ‘clay in oil sands’ was motivated by two observations. The first was the growing interest in the effects of clay on oil-sands operations, in particular bitumen flotation and fine-tailings management. The second was the lack of a common basis of understanding, or even common vocabulary, among the various disciplines involved in investigating and managing those effects. The hope is that the contributions herein will summarize current knowledge about the effects of clay on oil-sands operations, while gently introducing basic theory, terminology, and methods that the authors and editors believe will facilitate further advances.