Aquifers and intrusive sheets links in Cambrian section at the Kuyumbinskoye field

Oil field development caused increase in the need for drinking, domestic and process water supply at the Kuyumbinskoye field. There is an obvious necessity of an in-depth study of the upper level of sedimentary mantel to locate aquifer in order to find and explore ground water. The subject of this study is Cambrian sediment of the upper structural level. Sediments of the Cambrian period are widespread over the entire area and comfortably occur on Teterskaya suite build-ups of Vend-Cambrian level. Sediments of Usoliyskaya, Belskaya, Bulayskaya, Angarskaya and Evenkiyskaya suites represent them. The build-ups of the trappean formation constitute an important part of the sedimentary column. In the Kuyumbinskoye area dolerite intrusions can be found in the sediments of Cambrian and Ordovician periods. According to the deep wells exploration data, three overlapping large beddings (sills) and numerous transgressive intrusions represent them. From the stratigraphic point of view, intrusive sheets correspond to Usoliyskaya, Belskaya and Angarskaya suites sediments. At the Kuyumbinskoye field in most wells, whose areas are contacting dolerite, we observed drilling mud absorption to a disastrous level. In some cases formation water influx was obtained. These observations show the increasing rock permeability at the contacting areas. Considering the high-permeability formations correspondence to intrusive sheets, a conclusion can be made that magmatic melts and concomitant aggressive solutions influence on reservoir properties of surrounding formations. However, sheets themselves can serve as shields preventing invasion of higher-rank brines into overlying aquifers and weak brines

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