The surge in the worldwide demand for hydrocarbons has resulted in considerable interest in drilling for unconventional resources. The Drilling Engineering Team has reduced the duration and cost of drilling wells by 80% in drilling days and 73% in well delivery cost while targeting more precise sand-channel targets in the Unconventional Field presented in the paper, during a time period of about 10 years. Optimizing the casing design (moving from seven casing strings to four casing strings), drilling practices (maximizing drilling parameters), and completion practices (moving towards 4-½-in cemented longstring instead of lower/upper completion), resulted in reducing the number of days and the associated drilling cost. The improvements include: Modifying hole sizes (slimming wells starting from 34-in section to 22-in section). Combining sections that were previously isolated (for example, combining the targeted sand-channel reservoir with a long shale interval above it in one section). Eliminating drilling liners and completion tiebacks (moving towards 4-½-in cemented longstring instead). Improving the drilling fluids program (moving towards high salinity NaCl polymer drilling fluid system for the shallower sections, and reducing mud weights needed to stabilize the long shale interval from 100+ pcf toward 70-80 pcf by utilizing OBM), Increasing top-hole rate of penetration by strategically moving all the directional nudging into the 8-½-in/8-⅜-in OBM drilled hole section, and decreasing cost of top hole bottomhole assemblies. Introducing new technology 8-½-in/8-⅜-in PDC bits that drilled the entire hole section with one bit. Introducing an updated combined logging program.
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.
This paper presents a success story of deploying new technology to improve geosteering operations in an unconventional horizontal well. A new-generation logging-while-drilling (LWD) imaging tool, that provides high resolution resistivity and ultrasonic images in an oil-based mud environment, was tested while drilling a long lateral section of an unconventional horizontal well. In addition to improving the geosteering operations, this tool has proven the ability to eliminate the wireline image log requirements (resistivity and ultrasonic), hence reducing rig time significantly. The LWD bottomhole-assembly (BHA) included the following components: gamma ray (GR), density, neutron, resistivity, sonic, density imager, and the newly deployed dual imager (resistivity and ultrasonic). The dual imager component adds an additional 15-ft sub to the drilling BHA, which includes four ultrasonic sensors orthogonal to each other, and two electromagnetic sensors diametrically opposite to each other (reference figure 1). This new technology was deployed in an unconventional horizontal well to help geosteer the well in the intended zone, which led to an improvement in well placement, enhanced the evaluation of the lateral facies distribution, and allowed better identification of natural fractures. The dual images provided the necessary information for interpreting geological features, drilling induced features, and other sedimentological features, thus enhancing the multistage hydraulic fracturing stimulation design. In addition, an ultrasonic caliper was acquired while drilling the curve and lateral section, providing a full-coverage image of the borehole walls and cross-sectional borehole size. The unique BHA was designed to fulfill all the directional drilling, formation evaluation and geosteering requirements. A dynamic simulation was done to confirm the required number of stabilizers, and their respective locations within the BHA, to reduce shock and vibration, borehole tortuosity and drilling related issues, thereby improving over-all performance. Real-time drilling monitoring included torque and drag trending, back-reaming practices and buckling avoidance calculations, which were implemented to support geosteering, and for providing a smooth wellbore for subsequent wireline and completion operations run in this well. A new generation dual-image oil-based mud environment LWD tool was successfully deployed to show the multifaceted benefits of enhanced geo-steering/well placement, formation evaluation, and hydraulic fracturing design in an unconventional horizontal well. Complexities in the multifunctioning nature of the BHA were strategically optimized to support all requirements without introducing any significant risk in operation.
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