Abstract

Directional drilling technology, in addition to several other benefits, has aided the development of petroleum reserves in environmentally sensitive areas, and locations with limited surface access. Since their introduction almost four decades ago, improvements in positive displacement motors1 (PDM) technology have contributed immensely to this drilling process.

Steerable PDMs are normally run in alternating "sliding" and "rotating" modes, in accordance with well profile requirements. As operational objectives became more challenging, it became evident that the industry had reached a plateau, with regard to PDM effectiveness2. Most wells now have 3-D profiles, extended reaches (ERD) and much deeper targets. Directional wells have comparatively higher operational costs, which grows exponentially with increases in well profile complexities.

To help drill such intricate wells effectively, at manageable operational costs, industry research efforts have focused on the development of expert technologies3,4,5 and products, one of which is the rotary steerable tool6,7 (RST). These tools achieve needed changes to wellbore trajectory (inclination and azimuth) while the drill string is in full rotation—rotary mode drilling. This advantage improves hole cleaning and wellbore quality. Complete rotary mode drilling, made possible with RST tools reduces wellbore tortuosity, torque and drag.

It enhances weight on bit (WOB) transfer and drastically improves rate of penetration (ROP).

RST tools are extremely complicated and have high maintenance costs, because of their architecture, component life and the harsh environments in which they are used. However, when the benefits listed above for RST drilling are achieved, substantial savings in operational costs are realized. In RST drilling programs, it is critical to use the appropriate drill bit technology, since the drill bit plays a huge part in the possible achievement of the identified RST benefits.

This paper will discuss the functional medium of RST tools. It will describe the development of a new PDC bit technology, which has been specifically engineered to establish operational compatibility with RST tools and enables achievement of their operational benefits. Performance improvements achieved with the specialized PDC bit/RST tool combination will also be discussed.

Background

PDMs have played a major role in the evolution of directional drilling technology. However, their inherent technical and operational inefficiencies, which had previously been known, have amplified as well profiles and performance objectives have become more challenging.

The sliding and rotating modes of PDM drilling have distinct negative effects on performance efficiency. The ROP differences between the sliding and rotating modes of drilling have been extensively quantified in the industry. Depending on the type of bit used—Roller cone (RC) or Polycrystalline Diamond Compact (PDC)—ROP reductions in the order of 45–70% are normal during sliding.

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