Tyler Cobb
Dan Scott
Bob Welch
Baker Hughes
Polycrystalline diamond compact drill bits continue to make strides in improving their drilling efficiency and range of use, but roller-cone drill bits are frequently called upon to perform in applications demanding high levels of steerability. Roller cones, with their innate side-cutting ability and low levels of torque, are ideal for achieving high build-up rates, and for directional drilling through difficult formations such as ones with high interfacial severity (interbedded), conglomerates, and abrasive sections.
Throughout the industry, there are increasing demands for roller-cone bit technology to handle challenging directional applications in wells with intense dogleg severities and high build-up rates in extended-reach laterals. Directional well profiles require the drill bits to cope with damaging side and cyclical loading forces, something that traditional roller-cone drill bits were not engineered to handle. The introduction of application-specific drill bit designs using premium drill bit technologies is resulting in longer bit life for operators in a broad range of difficult drilling environments. These technologies include two types of advanced seals, patented shirttail and leg hardfacing, and the newest generation of diamond inserts.
The drilling application review team (DART) process is Baker Hughes’ method for solving the most difficult drilling problems with their customers. This process brings together a cross functional team consisting of experienced application engineers, expert bit designers, technical marketing representatives, and, most importantly, the customer. Once the team defines the drilling problems and objectives, the members pool the resources at their disposal to design, test, review (redesign/test if necessary), and implement bit solutions.
Heel and gauge diamond enhancement features.
When a drill bit is used in high-angle applications on a directional assembly – regardless of whether it is a rotary steerable system or a bent-housing motor – the bit will certainly experience unnaturally high levels of forces on the outer-most (heel row) tungsten carbide inserts (TCI) due to the nonvertical orientation and cyclical loading characteristics.
In this environment, traditional cutting structures and carbide grades common in general-purpose roller cones are prone to high rates of wear and severe damages on the heel row. The loss of usable heel inserts allows for an undesirable direct formation contact on the cone steel and in the seal area, resulting in heat and wear that can quickly lead to premature bearing and seal failures. To counter this wear characteristic, the DART process has developed cutting structure design methods to identify optimum TCI carbide grades, insert shapes, and insert placement to enhance cutting structure life and drilling efficiency.
Vanguard Tricone drill bits have the flexibility of using one of two premium, patented seals. The high aspect ratio elastomer seal is a versatile option that has field-proven performance in a broad range of applications. Another option is the third generation metal-face seal that exchanges the dynamic elastomer seal for a patented metal-on-metal seal that has an increased capacity to handle high temperature and high speed drilling.
Shirttails are the upper portion of the bit leg adjacent to the cone that helps prevent the formation from coming into direct contact with the seal area. In directional intervals, the forced inclination of the drill bit means the shirttail and bit leg are prone to severe wear that can lead to early bearing failures. Traditional methods of leg protection using TCI compacts and/or a bead of hardfacing have proven inadequate for providing an appropriate level of shirttail and leg protection from abrasive borehole walls in directional applications. This hardfacing process has proven to be successful in reliably protecting bit bodies and seal areas.
If heel row durability and wear resistance is still an issue or concern, Vanguard Tricone drill bits also offer a variety of diamond enhancement configurations for overcoming this wear characteristic. As reported in the Society of Petroleum Engineers literature, diamond enhancements offer unmatched wear resistance in abrasive or heat-checking prone applications.
The diamond Vanguard heels (DVH) use a high quality diamond material that allows for a more aggressive insert shape to be used, providing enhanced rate of penetration potential with extremely wear-resistant properties in the critical heel row.
One particular drilling challenge in Asia consisted of an 8½-in. horizontal section through abrasive sandstones. Typically, bits were being pulled for low penetration rates and exhibited bad dull conditions, especially in regard to the outer portion of the cutting structure, and failed seals. Working with the customer to identify their drilling objectives, Baker Hughes initiated their premier DART process to design a drill-bit solution for this interval.
After the first round of designs and field tests were complete, the team felt there was more performance to be found beyond this first solution and continued to pursue better design methods, technology, and material options. The final proposed solution was a directional tricone bit with metal face seals and DVH.
The first run was a no-test, but in the second run, the VMD-68DVHX1 surpassed the field Krev average, despite being challenged with two sidetracks. In the third run, a new VMD-68DVHX1 bit was pulled for hours after 678 Krevs – a 30% improvement against the field Krev average – and came out in a significantly improved dull condition with all seals effective and in-gauge. The operator was pleased with the leap in drill-bit performance.
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