Infrasound induced by blasting in a limestone mine propagates to the houses in a neighboring village and vibrates their windows, doors, furniture and so on. This infrasound causing vibration becomes an apparent problem for the limestone mine near a village. The most effective way to reduce the vibration is to reduce the blasting scale, but this cannot be performed because of low efficiency for mining. Another effective way is to shift and reduce the dominant frequency of infrasound by changing the delay time of blasting caps so that it may not overlap the resonance frequencies of vibrated objects, but the necessary conditions to do so have not been shown.In this paper, in order to propose the necessary conditions for setting an optimal delay time of blasting caps to reduce the vibration, the infrasound of many patterns of blasting was measured in the face of Ube-Isa Limestone Mine and at a neighboring house of the mine. At the neighboring house, the windows vibration was also measured. From the analyses of these measured data, it was found that the longer delay time of blasting caps is necessary to reduce the lower frequency component causing a large vibration, and shorter one is necessary to shorten the duration of blasting and reduce the resonant vibration. Then, in order to satisfy these conflicting conditions, a varied delay time of blasting caps was proposed and tested. As a result, the windows vibration was reduced 60% in total energy and 24% in maximum displacement compare to the minimum vibration of usual blasting using a fixed delay time of blasting caps.

Demands for reutilizing existing slots on the offshore platform are expected to rise to maintain oil and gas productivity by drilling and completing the well to different targets, whereas most of the slots are occupied in mature fields. Slot recovery operations are one of the solutions to recover occupied slots. Different slot recovery techniques have been executed in the Offshore Abu Dhabi field, which include cut & pull, milling, Casing Pulling Tool, and Conductor Deflector Tool techniques which are time-consuming and require high overpull to release the casings. The hollow bit is a slot recovery technique that enables the user to recover casing by the standard fishing tool (i.e., casing spear and overshot) without excessive overpull which inherits a risk of surface equipment damage and safety issues on the rig floor. Moreover, overcoming the strong cement bonding between a 30" conductor and 13-3/8" casing is difficult and is dependent on the cement condition. The casing is cut into short intervals to be pulled out which results in a long operation duration. Hollow bit removes the annulus cement between 30" conductor pipe and 13-3/8" casing by washing over the cement. Casing cuts can be minimized since the removal of cement from the annulus overcomes the cement condition uncertainties which results in a shorter slot recovery duration. This paper presents the 3 hollow bit field trials conducted in 2021-2022 in Offshore Abu Dhabi. Lessons learned accumulated from each trial were implemented in subsequent wells to improve the performance. Performance was increased by 60% compared to other slot recovery methods by reducing the operation duration from 20.8 days to 12.5 days. Best practices that can be implemented to similar application by hollow bit are also presented.

107 new wells are planned to be drilled primarily from two new Artificial Islands during the period of one project from 2023 to 2029. The number of existing wells in the oil field has reached 1,068 Mother bores, 2,178 wellbores @16,453,666ft total well length as of December 2019. Trajectories, especially from existing Artificial Islands, are getting more complex so as to avoid collision issues, and it is becoming increasingly difficult to drill accordingly. It is of great importance to assure that it is possible to drill the planned wells without serious collision issues before the execution of the project. Trajectories for planned wells were drafted one-by-one utilizing "DecisionSpace Well Planning" based on the predetermined slot allocation with the planned drilling pad design. Geological models are incorporated into DecisionSpace Well Planning. Therefore, formation tops were taken into account in order to make the trajectories more realistic. After that, trajectories were exported to "COMPASS" and anti-collision scan was performed on well-by-well basis. Anti-collision scan was performed among planned wells as well as actual wells. In case that one well has such serious collision issues that the well cannot/should not be planned based on company policy as a result of Anti-collision scan, trajectory or Landing Point (LP)/Total Depth (TD) location were adjusted. Then, Anti-collision scan was carried out again. If it was confirmed that there is no serious Anti-collision issues, trajectory was considered as final. It has been found that all the wells during the period from 2023 to 2029 can be drilled without serious collision issues by slightly adjusting LP/TD while satisfying several practical drilling requirements. Through the Anti-collision study, following recommendations for the avoidance of collision were obtained:Multi Station Analysis (MSA)+In-Field Referencing (IFR)+SAG correction should be applied in all the Jack up operations as well as Island operationsApplication of real-time MSA should be considered on a case-by-case basisMWD survey for the past wells should be corrected with IFR+MSA to reduce EOU sizeRe-Gyro jobs for low-quality survey wells should be enhanced around the project's development areaKick off point (KOP) should be deeper in the center of the drilling pad and shallower in the edge of the drilling pad

Good cementing practices are required to achieve effective zonal isolation and provide long-term well integrity for uninterrupted safe production and subsequent abandonment. Zonal isolation can be attained by paying close attention to optimizing the drilling parameters, hole cleaning, fluid design, cement placement, and monitoring. In challenging extended reach wells in the UAE, different methods were employed to deliver progressive improvement in zonal isolation. Cementing the intermediate and production sections in the UAE field is challenging because of the highly deviated, long, open holes; use of nonaqueous fluids (NAFs); and the persistent problem of lost circulation. Compounding the problem are the multiple potential reservoirs; the pressure testing of the casing at high pressures after cement is set; and the change in downhole pressures and temperatures during production phases, which results in additional stresses. Hence, the mechanical properties for cement systems must be customized to withstand the downhole stresses. The requirement of spacer fluids with nonaqueous compatible properties adds complexity. Lessons learned from prior operations were applied sequentially to produce fit-for-purpose solutions in the UAE field. Standard cement practices were taken as a starting point, and subsequent changes were introduced to overcome specific challenges. These challenges included deeper 12 ¼-in. sections, which made it difficult to manage equivalent circulating densities (ECDs), and a stricter requirement of zonal isolation across sublayers in addition to required top of cement at surface. To satisfy these requirements, several measures were taken gradually: applying engineered trimodal blend systems to remain under ECD limits; pumping a lower-viscosity fluid ahead of the spacer; using NAF-compatible spacers for effective mud removal; employing flexible cement systems to withstand downhole stresses; and modeling the cement job with an advanced cement placement software to simulate displacement rates, bottomhole circulating temperatures, centralizer placement, mud removal and comply with a zero discharge policy that restricts the extra slurry volume to reach surface. To enhance conventional chemistry-based mud cleaning, an engineered scrubbing additive was included in the spacers with a microemulsion-based surfactant. The results of cement jobs were analyzed by playback in advanced evaluation software to verify the efficiency of the applied solutions. This continuous improvement response to changes in well design has resulted in a significant positive change in cement bond logs; a flexural attenuation measurement tool has been used to evaluate the lightweight slurry quality behind the casing, which has helped in enhancing the confidence level in well integrity in these challenging wells. The results highlight the benefit of developing engineering solutions that can be adapted to respond to radical changes in conditions or requirements.

Reservoir sections in MRC (Maximum Reservoir Contact) & ERD (Extended Reach Drilling) wells are mainly designed to drill 8 ½" hole, because of drilling limitations with smaller hole size. However, slim hole sizes offer opportunities to revitalize existing wells using re-entry drilling techniques in association with MRC and ERD designs. This paper discusses the best practices to be implemented in order to mitigate risk, reduce complexity and ensure improved drilling performance. Re-Entry wells in the field have a risk of well integrity issues such as corroded 9 5/8" casing. In order to mitigate this risk, the corroded 9 5/8" casing should be covered by 7" liner & tied-back to surface before drilling reservoir section. In this situation up to 18,000 ft of 4" DP is used in the wells to drill 6" hole and run 4 ½" lower completion. Offset well analysis, whip stock selection criteria, BHA design, drilling fluid selection, drilling and tripping practices based on torque & drag and hydraulics calculations are most important to achieve the well objective. The Slim hole MRC well was completed without any issues and achieved good drilling performance. It was observed that the actual drilling parameters such as torque, drag and stand pipe pressure were less than simulated parameters. NAF was selected in the section to reduce the friction factor, while motorized RSS and a reamer stabilizer were used in the BHA to reduce torque, drag and ensure a smooth well profile. A back reaming practice was implemented in hole section to reduce dog leg severity and the open hole was eventually displaced to viscosified brine to minimize the friction factor for running the 4 ½' lower completion. 8500 ft of 6" hole section was drilled and TD was reached at +/- 19,000ft within 50 days including recovering the existing completion, drilling 8 ½" & 6" hole and running completion. This paper aims to contribute to the oilfield industry by sharing the successfully implemented engineering design and operation execution methodology to overcome the complexities present in Re Entry Wells MRC/ERD wells required to be drilled with slim hole conditions under an optimal cost, time effectiveness and low risk.