REDUCING THE NEGATIVE IMPACT OF WORKOVER FLUIDS ON SOROVSKOE OILFIELD SANDSTONE FORMATION BY THEIR MODIFICATION

Abstract

Relevance. Sandstone reservoirs of Western Siberia are predominantly hydrophilic in nature and contain a wide variety of clay minerals. When exposed to the bottomhole zone of wells with such technological compositions as spacer fluids, killing fluids, acid compositions and other aqueous chemical reagents used during well servicing and workovers, well productivity decreases due to the decline of oil relative phase permeability and swelling of clay minerals of the rock. Reducing the negative impact of workover fluids can be achieved through the selection and adaptation of effective spacer fluids and surfactants, through a complex of analytical and laboratory studies. The aim of the research is to select the effective spacer fluids and surfactants to reduce negative impact on the reservoir properties of the Sorovskoe oilfield BS7 formation. Objects: spacer fluids, clay stabilizers and surfactants. Methods. This aim was achieved through a review of domestic and foreign experience in the use of reagents – clay stabilizers and surfactants – in the conditions of hydrophilic clay sandstone reservoirs and a set of laboratory studies to assess the impact of spacer fluids on the formation rock by determining the swelling coefficient of disintegrated rock in these fluids and core tests under thermobaric conditions of the formation. The minimally effective dose of surfactants was determined based on the results of measuring the surface tension at the «spacer fluid – oil» phase boundary. The stability of the reagents under the temperature and salt aggression, as well as the assessment of the risks of the manifestation of incompatibility of the reagents with the formation fluids and the acid compositions was carried out by the bottle tests. Results. The minimally effective dose of surfactant has been determined, as well as its stability to temperature and salt aggression under the reservoir conditions. The physicochemical compatibility of solutions of surfactants and spacer fluids was tested with oil from the BS70 formation of the Sorovskoe field and acid compositions used at the field. Based on the complex of studies carried out, it was found that surfactants based on quaternary ammonium compounds and spacer fluids based on sodium chloride (with a density of 1140 kg/m3) and potassium chloride (with a density of 1140 and 1070 kg/m3) provide the greatest core model permeability build-up. These fluids and reagents are recommended for use in wells workovers, as well as in the technology of acid treatment of the bottomhole zone in the conditions of the BS70 formation at the Sorovskoe field.

Keywords

• sorovskoye oilfield
• spacer fluid
• workover fluid
• killing fluid
• acidizing
• clay swelling
• relative phase permeability
• surfactants
• clay stabilizers
• sandstone formation
• core tests