Saline fluid interaction experiment in clastic reservoir of lacustrine basin

Abstract

The south of western Qaidam Basin depositional environment was mainly a saline lacustrine basin in the Cenozoic. Great breakthroughs have been made in this area. Previous achievements indicated that saline environment improves the conversion rate of hydrocarbons, which was beneficial for hydrocarbon generation, but there is still not much research on the alteration of reservoirs in saline environment. This experiment simulates physical–chemical reflection between fluid and rock in geological conditions, and further study is made on the influence of saline water on reservoirs. By analysis of reservoir properties and capillary pressure alteration pre–post interaction, it is possible to study the negative effect that saline environment has on reservoirs. The mechanism is as below: The precipitation of saline minerals has negative effects on reservoir properties; the saline minerals occupied part of intergranular pore, which reduced reserve attributes; thinner pore throats are more easily blocked, which increases deviation of pore structure and permeability. The fluids of saline basin were rich in potassium ions, which have an inhibiting effect on dissolution of feldspathic, and are unfavorable for the formation of dissolved pores. The saline fluids contained a large number of potassium ions to provide material conditions for the reaction where the smectite and andreattite changed into illite. The higher ionic concentration of potassium ion, the more slender illite was generated. These slender minerals more easily blocked throats and pore, which in turn lowers the permeability of rock.