Pre-Caspian basin wells in salt-gypsum beds require an optimized drilling fluid

摘要

Drilling wells through the ultrathick, salt-gypsum beds in the pre-Caspian basin requires an optimized drilling fluid. The fluid must effectively inhibit salt-gypsum creep, salt dissolution, and hydration expansion in the water-sensitive formation to keep the borehole stable under high pressure and high temperatures. A large portion of the basin lies in the southern part of Kazakhstan, and the rest is in Russia. With the drilling characteristics of the ultrathick salt-gypsum bed in the Kolzhan block, the recommendation from the optimization process is for the use a zwitterionic polymer-KCI saturated brine drilling fluid. Well SLK3 is a wildcat well drilled through salt by the Central Asia project department of Shengli Oilfield in the Kolzhan Block. The planned depth was 5,500 m. The well used the zwitterionic and polysulfonate saturated brine drilling fluid after the upper borehole. The bottom of the salt-gypsum bed was at 5,026 m and the thickness of salt beds was 4,426 m.