An Investigation of Heavy-Foam Properties for Offshore Drilling

Abstract A unique problem in drilling oil and gas wells offshore is the narrow window between the formation pore pressure and fracture pressure. The current drilling practice with constant-density drilling fluids requires excessive casing programs and larger, more expensive rigs to drill offshore wells. Although different techniques, such as dual-gradient drilling, have been used to ease the problem, they are limited to certain geological conditions. This study investigated the properties of heavy foams that may be used in offshore drilling to solve the problem. In this study we performed a systematic investigation of heavy foams which are defined as the foams generated using weighted water and brine. Our study focused on rheological modeling, polymer selection, and foam properties. This paper presents our experimental results from 5 heavy foam systems namely water-barite-nitrogen system, water-hematite-nitrogen system, water- KCl-nitrogen system, water-CaBr2-nitrogen system, and water-CaBr2-barite-nitrogen system. We conclude that all of the investigated heavy foams behave as Bingham-Plastic fluids with an exception that the heavy foams from the water-barite-nitrogen system show Power-Law behavior. The best heavy foams from the water-CaBr2-nitrogen system were generated using Guar Gum as viscosifier. Foams from the water-CaBr2-nitrogen system have better stability and quality than those from the water-KCl- nitrogen system. Data from this study may serve as a base for selecting heavy foams in drilling offshore oil and gas wells.