This paper will detail the coordination between multiple teams and across technical discipline groups to successfully drill a ϩ28000 feet (ft.) measured depth (MD) horizontal appraisal well in a high temperature, high hydrogen sulfide and carbon dioxide (H 2 S/CO 2 ) environment and acquire high quality measurement and logging while drilling (MWD/LWD) data.Strategic tripping practices were used to reduce the risk of temperature related MWD/LWD tool failures. Extensive fluid engineering work was conducted, to design a fit-for-purpose mud system to meet Al Hosn Gas's handling requirements. Effective surface gas removal techniques were used to preserve high quality drilling mud and insure communication with the MWD/LWD tools. Hole cleaning efficiency was determined and maintained by monitoring drilling trends against calibrated models. In addition, the bottom hole assembly (BHA) drive system was designed to maximize power at the bit.Specific drilling parameters allowed for a high rate of penetration (ROP) that effectively reduced exposure time of the down-hole tools to very high temperatures minimizing tool failures. Carefully planned fluid engineering provided constant stable mud properties, which allowed the removal of H 2 S/CO 2 , and insured adequate borehole cleaning and lubricity to alleviate torque and drag. This resulted in high quality borehole images. Lubricants to reduce torque to manageable levels were selected after exhaustive in-house testing. Similar fluid engineering practices were used to select H 2 S scavenger. An extension of the horizontal section beyond the directional plan was accomplished within operational limits set by Al Hosn Gas after all drilling risks were fully assessed.Acquisition of required high quality LWD data was successfully accomplished. LWD borehole images were available only in memory mode, however, azimuthal resistivity curves helped in making geosteering decisions in the absence of the real-time borehole image data. Despite the well being drilled in the pay zone for its entirety, a measurement after drilling (MAD) open-hole log was employed to acquire missing density data that was required after a tool failure. A full petrophysical analysis was completed using the recorded memory data. It was included in the reservoir geo-cellular model and helped to define reservoir properties with a high degree of confidence.Close collaboration and trust between all partners to continually challenge and redefine perceived technical and operational boundaries led to the successful drilling of Al Hosn Gas's longest well. All teams and personnel were aware of the challenges and developed solutions to acquire excellent MWD/ LWD data in one of Al Hosn Gas's most ambitious wells, to date.
Two optimized polymer/borate/salt (PBS) fluid loss systems were recently implemented in two different ADNOC Sole Risk (ASR) wells while drilling different troublesome formations in the Arabian Gulf which are prone to losses. The first well (Well A) was drilled through the fractured Upper Khuff Formation, and the second well (Well B) through porous Arabs and fractured Diyab/Jubaila groups. The application of the PBS systems enabled the rigs to regain circulation and successfully drill to the total planned depth with less non-productive time attributed to curing losses. The wells involved several different key objectives; however, zonal isolation and logging were critical to both. In addition, the ability to control losses, even at an acceptable rate for one of the wells, allowed the team to proceed with the critical logging program. If not mitigated, losses could have resulted in a well-control situation. Controlling the losses on Well A allowed the first unimpeded logging suite, including high quality imaging, pressure sampling and avoidance of a liner run. After logging the section, drilling was resumed to the planned section total depth, and the liner was run and cemented successfully. The application of the PBS system in Well B allowed multiple troublesome formations (Arabs/Diyab/Jubaila/Gulailah/Sudair) to be drilled as one interval and successful isolation of these zones. The losses were completely cured after applying this system in the correct zone. The total planned depth was attained and the casing landed and cemented. The solution for these loss-circulation challenges when drilling was the development of a faster, as well as flexible, setting and crosslinking PBS system that could effectively bridge and/or adhere to the formation rock. The optimization also included extending thermal stability of the set plug to maintain a workable loss rate at the anticipated elevated temperatures and simulations to ensure the system would agglomerate and adhere to the limestone/dolomite rocks. Pre-planning started nine months prior to drilling these wells. The predicted challenges ranged from managing losses to developing contingencies for total loss of circulation through the above-mentioned formations. Contingency systems were devised using a decision tree and rig instructions were prepared for every wellbore/scenario. The planning process included determination of a pumpable volume that would facilitate spotting this fluid loss system only once. This paper outlines the successes achieved in curing loss circulation in the 8⅜-inch section of Well A within the Khuff formation and the 12¼-inch section of Well B within the Diyab group formation. These were drilled in ASR Arabian Gulf region as shown in Fig. 1. Figure 1Location of the ASR wells in the Arabian Gulf.
A review of lost circulation plans, contingencies, recaps, and methods used to primarily prevent losses in the upper-hole sections drilled in the offshore region of the Arabian Gulf was compiled in an effort to ascertain which lost circulation treatments and/or combinations were historically effective or ineffective for regaining circulation especially after total losses, whereby total planned depth was achieved with little to nil non-productive time (NPT) as related to drilling fluids. This evaluation highlighted numerous inconsistencies and excessive time committed to combating losses whereby the critical path was marginalized. While these wells comprised sole objectives, their upper-hole sections were drilled through known troublesome formations often with the same result. It was surmised that the type of lost circulation material (LCM), combinations of LCM, and frequency of use contributed little to no benefit in particular circumstances. Subsequently, this review was undertaken to ascertain if time could be saved with more prudent utilization and/or tactics when utilizing LCM to combat losses. A well-known application of LCM is its usage as background solids to mitigate fluid loss in troublesome wellbore sections primarily due to the relatively inexpensive cost, availability, ease of use, and compatibility with the drilling fluid. LCM are supplied in a myriad of sizes, types, textures, and applied in varying concentrations and combinations. This review details numerous LCM types and combinations in addition to various pills. While attempts were successful in stopping losses in the upper-hole sections, success was sometimes temporary as subsequent drilling operations would, in some cases, realize losses greater than the established trigger rate. The ensuing discussion includes a synopsis of challenging vugular and/or fractured carbonate formations in the UAE and Copper Ridge Formation in the US, a review of common and some uncommon LCM, the field results, and finally, lessons learned and strategies are propositioned. The selected LCM are contrasted with their application in formations of the upper-hole sections versus various loss scenarios and results.
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