Water of Productive Oil Strata

subterranean waters that accompany oil in producing formations. In terms of its occurrence in an oil-bearing bed and its relation to an oil pool, a distinction is made among edge water, which is situated below the oil pool; bottom water, which is located at the foot (footwall) of a bottom-water drive field; top or upper water, which is confined to the upper (head) part of an oil-bearing bed; connate water, which envelops the surface of pores and saturates the most minute capillary interstices in an oil-bearing bed; and artificially injected water, which is pumped in to maintain pressure during development of an oil pool.

Edge water, bottom water, and lower waters most often have chloride or chloride hydrocarbonate, calcium-sodium or sodium, nonsulfate or low-sulfate ionic composition. In terms of the degree of mineralization, they may be salty or briny; in terms of gas composition, they may be methane and nitrogen-methane waters. Waters usually exhibit little variation in composition over large areas, since they are located not only within oil deposits but also between them. Waters that are in direct contact with oil deposits (edge and bottom waters) often have specific characteristics, such as high mineralization, gas saturation, and content of homologs of methane and benzene and of ammonium and various metals.

The study of water of productive oil strata is very important in prospecting and exploration for oil deposits and in their exploitation. In a number of instances, such waters are used as therapeutic mineral waters or are extracted for the purpose of recovering the iodine, bromine, boron, radium, barium, strontium, and other valuable substances contained in them.