Improved Torque and Drag parameters using Solid Expandable Tubulars Enhance Extended Reach Well Construction
Advances in modern well construction techniques have been have focused drilling deeper, longer, more cost effective extended reach drilling (ERD) wells. This is driven by current economics: the easily accessible land based or shallow water based reservoirs have, in large part, already been exploited. The larger undeveloped reservoirs remain in inaccessible locations. Deep water and inaccessible surface locations have been pushing the development of technology to push back the physical limits of extended reach drilling and to make moderate extended reach drilling more economic. Solid expandable tubulars are one such technology. This technology was developed specifically to allow additional casing strings to be run to cover up problem zones to facilitate drilling a well to the deeper zone or extended reach target. Expandable technology is seen as a way to reduce the overall resources required to construct an extended reach well. The complexity and cost of the rig, the drill string, the bits, mud products, cement, and, of course, the casing were projected to be reduced significantly, resulting in lower overall cost. These projections have happened in some cases1. It is generally hoped that this will culminate in the successful wide application of the mono-diameter well described elsewhere in the literature. These general benefits that have been expected to be realized on extended reach wells are significant on their own, but it is now known that there are secondary effects that may have a positive cumulative effect on the reach available and the cost of drilling certain types of extended reach wells. One of these areas is the effect on the torque and drag limitations on the new types of types of casing designs and drill string configurations now possible. Although there are many possible limiting factors, the torque and drag on an extended reach is often seen as the critical limiting factor in the reach that is actually achievable. To date, efforts have been made to mitigate these effects through judicious control of drilling fluid properties as well as through the use of rotary steerable drilling tools among other technologies, drill string friction reducing devices, and other mechanical improvements. Both the torque and drag of the drill string are effects that are primarily influenced by geometric conditions such as dog leg severity (DLS) and casing open whole size vs. drill string size. Torque and drag are also influenced by “friction factor” and by drill string dynamic conditions such as axial and rotary motion that overcome friction. The use of solid expandables has several distinct effects that can be favorable for drilling ERD wells. The surface roughness of post-expanded, solid expandable tubulars — by the nature of their manufacturing requirements and forming techniques as well as their antifriction coatings — will usually be substantially less than the roughness of comparable seamless casing. The second, and far more important effect, is that a more favorable drill string-casing geometry that can reduce the tendency for helical buckling or drill string lock up. In a case study, the data supporting the positive effect of solid expandable tubulars on drill string torque and drag will be demonstrated. Surface roughness data and frictional effect data from drilled wells will be considered. This input modeled for an ERD well shows the theoretical drilling limit improvement from these effects in real example well.