Abstract A high-quality wellbore is generally considered to have (1) a gauge hole, (2) a smooth wellbore, and (3) a wellbore with minimum tortuosity. This paper will demonstrate that wellbore spiraling is the primary contributor to poor hole quality and that almost every well contains some degree of spiraling unless specific actions are taken to prevent it. Hole spiraling was first studied by Lubinski et al. in the 1950s, and they described it as a "crooked hole." Although the symptoms have been well recognized in the industry, only recently has a solution been proposed and tried specifically to cure hole spiraling. To implement the concept, two new drilling systems (a steerable motor and a rotary steerable) have been developed. Field data indicate that generating a straighter, high-quality wellbore has improved almost every aspect of drilling. These improvements include lower vibration, better bit life, fewer tool failures, faster drilling, better hole cleaning, lower torque and drag, better logging tool response, and better casing and cement jobs. Several case studies will be discussed to demonstrate the positive economic impact of producing a high-quality wellbore. Introduction Hole quality can have a profound effect on the total well construction time and cost and sometimes even determine the success of drilling a well. The importance of good borehole quality increases as extended-reach and offshore wells become more common, as they have in recent years.1, 2 In general, a good hole quality is measured by (1) hole gauge, (2) wellbore smoothness, and (3) total tortuosity. While some hole problems are a function of wellbore stability and must be addressed with proper mud weight, others arise as a result of poor wellbore geometry. For example, how accurately does the borehole itself follow the surveyed path? Does it follow a more or less helical path around the centerline of the planned well trajectory like a spiral? Poor wellbore geometry is an area that is often overlooked, but it is important that the following questions be addressed: Is hole spiraling prevalent? If it is, why haven't we known it? And what is a high quality hole worth? Hole spiraling is not easy to detect because MWD surveys are usually at least 30 ft apart. Because the collars will lie on the low side of the wellbore, the survey data would show very little trajectory variation. However, a sinusoidal form of borehole can be clearly seen by a wireline imaging log (see Fig. 1) or the formation evaluation logging tool data (see Fig. 2). Nieto et al.3 report that it is quite common to see boreholeinduced "sinusoidal" noise on logging tools, especially those relying on contact or proximity to the wellbore wall. Some pieces of data would indicate that spiraling is prevalent in many wells. One is a study4 that showed that wells drilled with a new steerable drilling system produced friction factors significantly lower than conventional steerable systems.