Many modern well construction techniques have beendeveloped with an eye toward drilling deeper, longer, andmore cost effective Extended Reach Drilling (ERD) wells.One notable technology that has contributed to this effort issolid expandable tubulars. This technology was developedspecifically to allow additional casing strings to be run tocover up problem zones and facilitate drilling the well to theERD target. Solid expanable tubulars also help to reduce theoverall resources required to construct the well. Projectionsshow that using them would significantly reduce the size orvolume, as well as the cost of the rig, the drill string, the bits,the cement, and, of course, the casing, resulting in loweroverall costs. This result has been born out in practice and willculminate in the single-diameter well described elsewhere.1The effects on ERD wells will be substantial, but there areimportant ‘side effects’ that can have a profound cumulativeeffect. The torque and drag on an ERD well is usually thelimiting factor in the actual reach possible. These limits aremitigated by drilling fluid properties and the use of rotarysteerable drilling tools among other technologies. Torque anddrag are primarily influenced by geometric conditions likedogleg severity (DLS) and casing open hole size vs. drillstring size, surface effects (commonly grouped together andnamed the friction factor), and drill string dynamic conditions(such as axial and rotary motion that overcomes the friction).The use of solid expandables has two distinct effects that canbe favorable for the drilling of ERD wells. An important effectis that more favorable drill string casing geometry is possibleand can reduce the tendency for helical buckling or drill stringlockup. Another important impact is the ability to use largerdrilling tubulars.This paper will examine data supporting the positive effectof solid expandable tubulars on drill string torque and drag.Data modeled for an ERD well shows the theoretical drillinglimit improvement from these effects in real example wells.Extended reach drilling limitations have been pushed outsignificantly in recent times. Advances in mud systems,geomechanics, and the advent of rotary steerable systems havesignificantly improved the ability to reach further to accesshydrocarbons. However, limitations, though receding, stillexist. To counter them, new approaches are being developedthat attack in various ways the traditional boundaries ofextended reach drilling applications.
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