Experience in Stimulating Multilateral Horizontal Wells using a Multilateral Reentry System and a Dispersion of Acid and Solvent and a Viscoelastic Diverting Acid

Abstract

The Bashkirian Formation within the Stepnoozerskoe oil field is represented by carbonate rocks with a complex geological structure characterized by high lateral and vertical heterogeneity. The reservoir temperature is about 23 deg C, the pressure does not exceed hydrostatic, the viscosity of oil in the reservoir conditions exceeds 200 cP, porosity and permeability of the reservoir vary widely. In 2016, a pilot project to drill 2 multilateral wells on the Bashkir Formation was carried out; each well has 4 sidetracks (fishbones). Development of the reservoir with multilateral horizontal wells based on the simulation results allows to accelerate oil production, significantly improving the project economics, and the presence of horizontal sidetracks mitigates the risks associated with high lateral heterogeneity and ensures maximum contact of the wellbore with the reservoir. To stimulate the inflow into the wells, it is necessary to conduct acid treatments. Two unique works were carried out in Russia with the use of a multilateral reentry system for detection and selective access into different boreholes. This system made it possible to orient and successfully enter the multilateral well with 4 open horizontal sidetracks for subsequent acid treatment. The treatment of the bottomhole zone was carried out with the help of self-diverting acidic compositions. In one of the wells, a buffer of hydrocarbon solvent, followed by steps of retarded hydrochloric acid injection and self-diverting acidic composition based on surface active agents was used. In another well, a dispersion of acid and solvent and a viscoelastic diverting acid on a polymer free base were used as a buffer. In this paper, the authors describe the experience of stimulating multilateral horizontal wells and a comparative analysis of the results obtained.