Abstract
Most of the technological improvements seen in the drilling of wells with a "pneumatic fluid" (hereafter referred to as air) have come from the mining industry which is primarily associated with shallow large bore wells. The oil and gas industry has failed to make the same technological improvements in "air drilling" as compared to wells drilled with liquid systems. Air drilling has remained a "step child" and treated as an art rather than a science. One of the primary differences has been the failure to treat it as a integrated system like liquid drilling. In "air drilling" components are pieced together with little regard to other components.A air drilling system is actually more complex than a liquid one and requires more engineering to be successful. Because the pneumatic fluid is compressible there many improvements that can be made to manipulate downhole pressure and velocity which cannot be done in a liquid system. It is actually advantageous to divert a portion of the pneumatic fluid into the wellbore before it reaches the bit. However to do this with consistency and divert the proper volumes at the proper depth a Pneumatic Fluids Drilling Model must be utilized which is rarely done. This paper presents new technology which has been proven in theory and practice to improve air drilling performance. The technological improvements include a model which accurately demonstrates downhole pressures, velocities and kinetic energy throughout the system so that various drillstring and wellbore geometry as well as pneumatic fluid volumes can evaluated quickly. The model demonstrates the effects of diverting a portion of the pneumatic fluid into the wellbore above the bit. The paper also describes a new tool the "downhole air diverter" or DHAD) which is deployed in the drillstring that can accurately divert the optimum amount of pneumatic fluid based on model recommendations. As a result of using this new technology to manipulate bottom hole pressures at the bit the energy normally lost to friction can be used beneficially resulting in lower surface compression cost, less hole erosion, higher penetration rates, longer bit life and a higher percentage of wells reaching TD without converting to incompressible fluids.
This paper presents conclusive data from bottom hole pressure tests demonstrating that the surge effect (Venturi Effect) which is used at the surface to draw pneumatic fluids away from the wellhead can also be created downhole to lower annular bottom hole pressures. By lowering this bottom hole pressure more velocity is created with less air and less friction. Case studies are presented demonstrating how this technology has been used successfully in the field under various wellbore conditions resulting in higher penetration rates, improved wellbore stability, longer bit life and overall reduced drilling cost.
