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Subsurface anomalies can present complex well construction challenges. These anomalies to name a few are irregular wellbore stress profiles, low fracture gradients that require complex mud programs and, in some cases, total fluid losses while drilling. Poor wellbore stability is a common result of such anomalies and service companies serving the industry develop technologies to address, mitigate against and overcome these issues. A gas well encountered such a challenge. While drilling the 17″ section complete fluid losses were encountered. These losses generally uncommon in the field and were attributed to a seismic anomaly. This resulted in poor wellbore stability and led to multiple lost BHAs and sidetrack attempts. The surface casing design did not allow for extensive remedial options so rather than continuing recovery operations it was decided to suspend well construction and spud an offset well 50 meters away. Equipped with the knowledge of the drilling problems from the direct offset, the potential problems they represent and considering the proximity, it was decided to introduce two engineered solutions to mitigate against these challenges and secure successful well construction. First, the surface casing design was modified and the 18-5/8″ casing was set deeper and second, casing while drilling (CWD) technology was introduced to drill for 13-3/8″ intermediate casing from the 18-5/8″ shoe to 13 3/8″ casing point (CP). During planning it was concluded that casing drilling technology would allow to simultaneously keep every foot drilled behind casing, under total losses conditions. Furthermore, CwD would minimize the open hole time compared to conventional drilling practices, an important factor when mitigating against risks from poor wellbore stability. Approximately 4.5 days after setting the 18-5/8″ surface casing, a 16″ CwD drill bit made-up to 13-3/8″ casing successfully drilled 1575 ft with total losses and cemented in place across an interbedded formation. This was a starkly different result compared to the direct offset where operations were suspended after many more days between setting the 18-5/8″ to decision to suspend.
Subsurface anomalies can present complex well construction challenges. These anomalies to name a few are irregular wellbore stress profiles, low fracture gradients that require complex mud programs and, in some cases, total fluid losses while drilling. Poor wellbore stability is a common result of such anomalies and service companies serving the industry develop technologies to address, mitigate against and overcome these issues. A gas well encountered such a challenge. While drilling the 17″ section complete fluid losses were encountered. These losses generally uncommon in the field and were attributed to a seismic anomaly. This resulted in poor wellbore stability and led to multiple lost BHAs and sidetrack attempts. The surface casing design did not allow for extensive remedial options so rather than continuing recovery operations it was decided to suspend well construction and spud an offset well 50 meters away. Equipped with the knowledge of the drilling problems from the direct offset, the potential problems they represent and considering the proximity, it was decided to introduce two engineered solutions to mitigate against these challenges and secure successful well construction. First, the surface casing design was modified and the 18-5/8″ casing was set deeper and second, casing while drilling (CWD) technology was introduced to drill for 13-3/8″ intermediate casing from the 18-5/8″ shoe to 13 3/8″ casing point (CP). During planning it was concluded that casing drilling technology would allow to simultaneously keep every foot drilled behind casing, under total losses conditions. Furthermore, CwD would minimize the open hole time compared to conventional drilling practices, an important factor when mitigating against risks from poor wellbore stability. Approximately 4.5 days after setting the 18-5/8″ surface casing, a 16″ CwD drill bit made-up to 13-3/8″ casing successfully drilled 1575 ft with total losses and cemented in place across an interbedded formation. This was a starkly different result compared to the direct offset where operations were suspended after many more days between setting the 18-5/8″ to decision to suspend.
During non-productive time (NPT) such as stuck pipe incidents, reducing the operational time and associated cost of the trouble mitigation should always be the goal. Therefore, the engineering team searched for new and innovative ways to reduce the NPT when stuck pipe incidents happen, and successfully utilized an existing technology in a new way not yet performed on a global basis. In seldom incidents drilling or tripping through unstable zones (especially when drilling through sticky shales and loose sandstone zones charged with downhole faults/fractures) with complete loss of circulation, severe tight spots, stalling tendencies, hard backreaming, etc. might be experienced. In the worst case, the pipe might get stuck and cannot be freed. The engineering team investigated several options to allow drilling and casing off the trouble zones in such incidents, while reducing the NPT in the same time. Sidetracking through open-hole and/or cased-hole whipstock, then utilizing level-2 casing-while-drilling technology to drill and case-off the instable zones was the best cost effectient option. Successful deployment of level-2 16-in × 13-⅜-in casing-while-drilling (CwD) technology through an 18-⅝-in cased-hole sidetrack whipstock and level-2 22-in × 18-⅝-in CwD technology through open-hole sidetrack led to drilling and casing off severe unstable sections in two separate wells in different areas of interest. The level-2 13-⅜-in CwD utilization to drill and case-off trouble zones through cased-hole sidetrack was the global first. The level-2 18-⅝-in CwD utilization to drill and case-off trouble zones through open-hole sidetrack was the country first. Both led to significantly reducing the non-productive time (NPT) resulted from the stuck pipe incidents in a cost effective manner. Extensive engineering simulations, technical limits, and risks assessment were set to insure flawless execution. During the job execution, the drilling performances were constantly monitored. The engineering simulations are updated using the actual parameters to ensure accurate measurements of the accumulated fatigue while being rotated to preserve the casing due to exposure to high dogleg severity (DLS) in the sidetracked wellbore. Furthermore, the hydraulics are optimized real-time to ensure hole cleaning without further increase in the equivalent circulating density. Even with no prior global experience of the utilization of this technology through such operation, the pursuit of the technical limit was to reduce the NPT as much as possible. The technical paper will highlight the planning steps, challenges, detailed engineering simulation, risks mitigations and engineered solutions, and the successful results of the deployment of level-2 CwD runs through sidetracked wellbores.
Drilling and completion of the surface and intermediate sections in some fields is extremely challenging due to wellbore instability, especially accomplished with complete losses. Such circumstances lead to several time-consuming stuck pipe events, when existing standard ways of drilling did not lead to a permanent resolution of the problems. After exhausting the available conventional techniques without sustainable success, unorthodox solutions were required to justify the well delivery time and cost. Here comes the Casing While Drilling (CwD), being the most time and cost-effective solution to wellbore instability. CwD is introduced at full throttle aiming at the well cost reduction and well quality improvement. The implementation plan was divided in three phases. The first phase was a remedial solution to surface and intermediate sections drilling and casing off to prevent stuck pipe events and provide smooth well delivery performances. After successful implementation of CwD first phase, CwD was taken to the next level by shifting it from a mitigation to an optimization measure. Each step of CwD shoe-to-shoe operations was analysed to improve its performances: drill-out (D/O) of 18⅝-in shoe track with CwD, optimum drilling parameters per formation and CwD bit design. Implemented in 19 wells, CwD shoe-to-shoe performances have been brought up or even above standard rotary bottom hole assembly (BHA) benchmark. Planning for third phase is undergoing whereby CwD is aiming to optimize a well construction to reduce well delivery time, by combining surface and intermediate sections thus eliminating one casing string. Numerous challenges are being worked on including open hole (OH) isolation packer which conform to and seal with the borehole uneven surface. Special "for purpose built" expandable steel packer and stage tool have been manufactured and qualified for the specific application. A candidate well has been chosen and agreed for first trial. The key areas of improvement include, drilling and casing off the surface and intermediate sections while competing with standard rotary BHA performances and slimming down the well profile towards tremendous time and costs savings. This paper encompasses details of constructions of various wells with sufficient contingencies to combat any expected hole problems without compromising the well quality while keeping the well within budget and planned time. It also provides an analysis of the well trials that were executed during the implementation of first and second phases of CwD implementation and the captured lessons learnt which are being carried forward to the next phase. This paper provides the technique on how CwD can be used to help with three aspects of drilling, successfully mitigating holes problems by reducing OH exposure time and to eliminate drill string tripping and modifying conventional casing design to reduce well time and cost by eliminating one casing string.
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