Chpater 4 - Downhole Equipment

Abstract

Air and gas drilling operations require some special subsurface equipment and drilling methods. This chapter explores the downhole equipment used in such operations. Deep direct circulation operations use rotary drill strings. Larger diameter shallow- and intermediate-depth wells are usually drilled with reverse circulation techniques. Two general types of drill strings are used: the standard drill string (used exclusively for deep direct circulation operations) and the dual wall pipe drill string (used exclusively for intermediate and shallow depth reverse circulation operations). There are three basic types of rotary drill bits used in air and gas drilling operations: drag bits, roller cutter bits, and air hammer bits. An example of numerical classification chart for insert drill bits is given. The bottom hole assembly is the section of the drill string below the drill pipe. It is this section of the drill string that determines how much weight can be placed on the drill bit and how “straight” a vertical borehole will be drilled with the drill string. Downhole surveys are used to describe the deviation of a drilled borehole from the ideal vertical centerline of the intended well. There are four types of drill pipe used in air and gas drilling operations: standard API drill pipe, heavyweight drill pipe, drill rod, and dual wall pipe. Drill strings used in direct circulation drilling operations are fitted with several safety valves.