Chpater 8 - Air, Gas, and Unstable Foam Drilling

Abstract

This chapter outlines the steps used to plan a successful deep air and gas drilling operation and illustrates the application of these steps and methods to the planning of a typical deep drilling operation. Deep drilling operations with air and gas drilling technology are used in the recovery of oil and natural gas and in the recovery of geothermal steam and hot water. The application of air and gas drilling technology is usually limited to either performance drilling operations in competent rock formations or under-balanced drilling operations in low-pressure reservoirs. The advantage of air and gas drilling operations is that the bottom hole annulus pressures can be designed to be below the reservoir bottom hole pressure. Air and gas drilling operations are different from traditional mud drilling operations and require more intensive attention on the part of the on-site drilling operation supervisor. Deep air and gas drilling operations use a variety of compressed gases as the drilling fluid. The majority of the operations use compressed air or membrane-generated nitrogen. Unlike the aerated and stable foam drilling fluids, the modeling of air drilling fluids is not a rheology issue. The major issues with air drilling fluids are downhole combustion and the ability of the air drilling fluid to carry formation water from the well.