In a recently drilled deviated well in an offshore field in UAE, severe cavings have been produced which led to difficulty in tripping out and stuck pipe events. A comprehensive study has been conducted to understand the chemical and mechanical behavior of the shales in the overburden. This paper focuses on how we approached optimization of drilling design and practices where well construction was concerned (namely casing design and mud formulation). This approach minimized mechanical and time-dependent chemical instabilities in the Fiqa, Laffan and Nahr-Umr shales. After the initial implementation of the optimized drilling practices, a complex multi-discipline study including time-dependent shale stability analysis provided recommendations for the problematic shales should they be kept open for long durations (to reach section TD, log and case). The time-dependent shale stability analysis included three major phases. The first phase was conducted based on the data for several selected existing wells. This phase resulted in obtaining so called field-based mud design criteria together with customized laboratory measurements. The second phase is to conduct a comprehensive geomechanical model to understand the mechanical behavior of the formations. In this study both 1D and 3D geomechanical models have been constructed honoring the anisotropic nature of the shales. The third phase was focused on selecting best mud system and optimizing the mud designs to prevent/minimize both mechanical and time-dependent chemical instabilities for shales layers with long exposure time. The problematic shales were penetrated at relatively high angles, requiring high mud weights and therefore leading to relatively high overbalance pressures which can cause high pore pressure increase in the shales with time. However, it is still feasible to select an optimum drilling fluid design for the desired mud system by optimizing salinity for the required high mud weights to avoid time-dependent instability. The Nahr-Umr shale, in general, was deemed to be more susceptible to mechanical and time-dependent chemical instabilities due to higher required mud weights and overbalance pressures. The Fiqa, Laffan and Nahr-Umr shale formations could be drilled using the recommended mud weights together with best mud formulations to avoid both mechanical and chemical time-dependent wellbore instability problems in the planned wells. The outcome of the study helps in keeping the shales open for longer period in highly deviated wells without any wellbore instability before casing runs. The workflow utilized for the shale stability analysis for Fiqa, Laffan and Nahr-Umr included an approach innovative for UAE to understand mechanical and chemical (osmosis-related) behavior of the problematic shales to develop recommendations for cases when the shales needed be kept open for long durations.
The long-term development of any mature field requires a fresh perspective of long MRC (Maximum reservoir contact) wells and increased well accessibility. To improve well accessibility the deployment of lower completion has been a mandate. Onshore UAE Field demands drilling Slim hole (6″ /6-1/8″ ) laterals and Slim Hole ERD (Extended reach drilling) wells with 4.5″ Uncemented Lower Completion. This paper highlights the innovative wellbore cleanout procedure prior installation of Lower Completions. Conventionally, using Water Based Mud (WBM) with high friction factors in 6″ Horizontal Hole (HH), two trips were required to reduce the friction factor prior running the Lower Completion. The optimized solution allowed wellbore clean-up and displacement of brine in one trip with drilling assembly (BHA). This innovative technique eliminated one dedicated trip for wellbore cleanout and thus saved millions in CAPEX and Business Plan days. The T&D data for 5 wells with dedicated cleanout trip were compared to clean-out with 6″ drilling BHA with viscous-lubricated brine. The 6″ BHA was optimized to fit with innovative dormant drilling scrapper and lubricated viscous brine was displaced in the Open Hole. A thorough hole cleaning procedure was formulated and was applied to all the wells. After analyzing over 5 wells, it was observed that in both runs, the one with 6″ BHA compared to dedicated cleanout-trip, the torque and drag values were similar and the effective reduction in friction factor was similar. This supported the elimination of planned dedicated cleanout trip and saved average 2 days/well and 27MM$ for year 2022. This optimized BHA design with enhanced hole cleaning procedure was a keystone in deploying slim 4-1/2″ lower completion in WBM system. This practice led to successful deployment of First Slim Hole ERD in UAE with 15000ft of 4-1/2″ lower completion with WBM system. This was a one-of-a-kind achievement in UAE.
High torque, friction factors, and pick up weights were major challenges encountered by a major operator in Abu Dhabi while planning to drill challenging extended reach development (ERD) wells with complex 3D profiles. Well torque and drag simulations showed that planned depths were not reachable with water-based muds. This paper describes the implementation of a mechanical lubricant, which resulted in significant decrease of the friction factors and turned an ERD well from not drillable to drillable with water-based mud. After analyzing several possibilities, the solutions were narrowed down to two: use either a new generation mechanical lubricant or a reservoir non-aqueous fluid (NAF). The complexity was amplified by the necessity to re-design a filter-cake breaker for NAF, were this option to be selected, due to the type of completion. This second option would also create a substantial cost increase for the operator for products and rig time; therefore, the decision was made to introduce a mechanical lubricant. A comprehensive study and lab tests were conducted to ensure compatibility and stability of the lubricant with a planned mud type at downhole conditions. The results of this study were promising enough for the operator to introduce this lubricant, aiming a substantial reduction in torque and drag to enable drilling of the longest horizontal section in the history of the project. Before addition of the mechanical lubricant, drilling continued with a conventional type of lubricant, noticing an increasing tendency of torque and drag tracking the predicted trends. At a certain stage, drillstring buckling was observed and drillpipe started to reach their limits. To mitigate these impediments, the mechanical lubricant was introduced into the drilling fluid. After reaching the optimum concentration, the mechanical lubricant eliminated buckling and provided significant reduction in torque, pick-up, and slack-off friction factors, respectively by 27%, 52%, and 42%. These parameter improvements facilitated continued drilling the well to final depth without reaching the drillpipe limits. Additionally, the well and bottomhole assembly (BHA) designs allowed for significant margins in case of a stuck pipe event, and based on the new friction factors, the well could be extended by 3,000 ft without reaching the drillpipe limits. The impact of this exercise in future ERD wells is considerable. It will simplify well and completion designs, improve logistics by reducing the amount of chemical movements, facilitate drilling fluids selection, and optimize the well cost. The paper covers the gaps related to drilling complex ERD wells with water-based drilling fluids. It provides detailed methods and procedures covering the suitable application of the mechanical lubricant and the extensive laboratory tests done during the planning stage, as well as the field application and results. The proposed solution can be used during the well planning process in any other area of the world.
Significant mud losses during drilling often compromises well integrity whenever sustainable annular pressure (SAP), is observed due to poor cement integrity around 9-5/8-in casing in wells requiring gas lift completion. Heavy Casing Design (HCD) is applied as a solution; whereby, two casing strings are used to isolate the aquifers and loss zones, thus ensuring improved cement integrity around the 9 5/8-in intermediate casing. Casing While Drilling (CWD) is a potential solution to mitigate mud losses and wellbore instability enabling an optimized alternative to HCD by ensuring well integrity is maintained while reducing well construction cost. This paper details the first 12 ¼-in × 9-5/8-in non-directional CWD trial accomplished in Abu Dhabi onshore The Non-Directional CWD Technology was tested in a vertical intermediate hole section of a modified heavy casing design (MHCD) aimed at reducing well construction cost over heavy casing design (HCD) as shown in the figure 1. A drillable alloy bit with an optimized polycrystalline diamond cutters (PDC) cutting structure was used to drill with casing through a multi-formation interval with varying hardness and mechanical properties. Drilling dynamics, hydraulics and casing centralization analysis were performed to evaluate the directional tendency of the drill string along with the optimum drilling parameters to address the losses scenario, hole cleaning, vibration, and maximum surface torque. The CWD operation was completed in a single run with zero quality, health, safety, and environment (HSE) events and minimum exposure of personal to manual handling of heavy tubulars. Exceptional cement bonding was observed around the 9 5/8 in casing indicative of good hole quality despite running a significant number of centralizers (with smaller diameter), compared with the conventional drilled wells (cement bond logging was done after the section). CWD implementation saved two days of rig operations time relative to the average of the offset wells with the same casing design. The rate of Penetration (ROP) was slightly lower than the conventional drilling ROP in this application. The cost savings are mainly attributed to the elimination of casing-running flat time and Non-Productive Time (NPT) associated with clearing tight spots, BHA pack-off, wiper trips. The application of CWD in the MHCD wells deliver an estimated saving of USD 0.8MM in well construction cost per well compared to the HCD well design. Additional performance optimization opportunities have been identified for implementation in future applications. The combination of the MHCD and CWD technology enhances cementing quality across heavy loss zones translating into improved well integrity. Implementing this technology on MHCD wells could potentially save up to USD 200MM (considering 250 wells drilled). This is the first application of the technology in Abu Dhabi and brings key learning for future enhancement of drilling efficiency. The CWD technology has potential to enhance the wellbore construction process, which are typically impacted by either circulation losses and wellbore instability issues or a combination of both, it can applied to most of the offshore and onshore fields in Abu Dhabi.
Loss of circulation while drilling the surface holes has become the main challenge in the Abu Dhabi Onshore developed fields. Typical consequences of losses are blind drilling and high instability of the wellbore that eventually led to hole collapse, drill string pack-offs and other associated well-integrity risks. Expensive operations including implementing aerated drilling technique, high water consumption and logistical constraints lead to difficulties reaching planned depth and running casing with added complexities of well integrity due to poor cement quality and bonding in the required isolation zones. Casing while drilling (CWD) is becoming a powerful method in mitigating both lost circulation as well as wellbore stability issues. This paper details the first 13 3/8″ × 16″ successful non-directional CWD trial accomplished in Abu Dhabi and the various advantages of the process. The Non-Directional CWD technology is used to drill vertical or tangent profiles with no directional drilling or logging (formation evaluation) requirements. The casing string is run with drillable body polycrystalline diamond cutters (PDC) bit and solid body centralizers are installed into the casing to achieve the required stand-off for cementing purpose. Some of the best practices applied to conventional drilling operations are not valid for CWD. The paper presents the methodology followed by the drilling engineers during the planning and preparation phases and presents a detailed description of the execution at the rig and the results of the evaluation including time savings, cement quality, rate of penetration, bottomhole assembly (BHA) directional tendency and losses comparison among others.The implementation of CWD saved the operator five days. The bit selection and fit-for-purpose bit design were critical factors for the success of the application. The interval was drilled (as planned) in one run through interbedded formations with a competitive rate of penetration (ROP). In this trial the interval consisted of 2,470ft with an average on-bottom ROP of 63.7 ft/hr, zero quality, health, safety and environmental (QHSE) incidents with enhanced safety for the rig crew.The technology eliminated the non-productive time (NPT) associated with tight spots, BHA pack-off, vibrations or stalls which it is an indication of good hole cleaning and optimum drilling parameters.Medium losses (10-15 BBL/hr) were cured due to the plastering and wellbore strengthening effect of CWD allowing drilling to resume with full returns.Well Verticality maintained with 0.3 degrees Inclination at section final depth.The drillable CWD bit was drilled out with a standard 12.25-in PDC bit in 1 hour as per the plan.
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