Drilling to the targeted depth of a well can be a challenge, considering the problems that may arise in the form of wellbore instability, mud losses, and/or differential sticking. The objective was to successfully drill a first-time implementation of an Oil-Based Mud (OBM) system with 60:40 Oil-Water Ratio (OWR). The OBM system was maintained within the specified parameters in terms of mud weight, viscosity, and fluid loss. The addition of primary and secondary emulsifiers in the system enhanced electric stability (ES). Moreover, solid control equipment will be monitored continuously for immediate action if necessary. Contingency plan and a surplus of chemicals will be provided to ensure a smooth drilling and a swift movement of operations. A fluid system was designed after extensive laboratory tests to analyze the optimal approach to drill using the first-time application of 60:40 OWR mud. It reduces the use of Diesel consumption by 26% in total OBM formulation, lowers the percentage of Low Gravity Solids (LGS) compared to the 80:20 OWR mud, and decreases the impact on the environment. Furthermore, the OBM was then reused in consequent wells with the addition of emulsifiers to reduce the cost. This paper presents successful first-time applications of the 60:40 OWR fluid till the targeted lower Burgan formation, interbedded sandstone and shale formation. A complete laboratory analysis comparison between previous wells drilled and the current application indicates no difficulties were faced.
Mature field necessitates drilling high angle and horizontal wells in order to improve wells productivity, reduce water coning and tapping multiple reservoirs. The operating company has endeavored to convert many of the Vertical wells in its mature fields into High angle and Horizontal wells by Side Tracking, primarily to reduce well cost and overcome restrictions in obtaining clear surface locations. Shale instability related problems were experienced in many Side Track wells in the buildup section. The whole deviation used to be ranging from 62 degrees on the top to 70 degrees on the bottom. The old wells used to be completed traditionally with a DLS of 5 – 5.5 leading to stuck pipe, hole collapse, multiple wiper trips, casing short landing etc. The operating company after extensive techno-economic evaluation has implemented a new and novel drilling technique to allow side tracking from an existing well, with inclination in the hole as low as possible, and land the well successfully with high dogleg severity. The new approach managed to reduce the deviation against the problematic formation to 50 degrees with a high dog leg severity up to 12 degrees / 100 feet. A high Build rate Rotary Steerable tool was used to reduce the measured depth and in some cases reduced inclination when drilling through unstable shale layers overlying the target formation. The High Build Rate tool also reduces the Vertical section thereby landing the well closer to its original hole reducing uncertainties in Landing. The Rotary Steerable was preferred due to its inherent advantage of continuous rotation that reduces differential sticking and enhances hole cleaning. Deep Kick Off increases deliverability of the depleted producer well by enabling placement of ESP Pumps at a deeper depth and overcome deferent formation with defiant pressure which improve mud weight management and overcome the stuck pipe problems in the shale zone by cutting through this shale with a low Inclination. It also enabled shorter measured depth, closer successfully landing and reduced open hole exposure time. Finally, the cost saving in this project can be summarized in reducing the buildup section by 45% which can be translated into a saving of more than 70 K USD per well.
While carrying out planned workover activities, production casing had to be tested to verify integrity. A shallow leak was observed across the production casing at about 1000 ft MD from surface. External and/or internal casing corrosion especially across relatively old wells, could lead to such inconsistency, moreover that major challenge to address and react such surprises online while operation meanwhile nothing to help as a pre-planning studies. Further production objectives require casing integrity as per ESP design to protect shallow aquifer sources. Numerous attempts to repair the casing leak by performing remedial squeeze operations utilizing conventional cement slurry designs proved unsuccessful. Other ideas were considered such as deploying a scab liner to cover the damaged casing section, however this was discounted as it would introduce undesirable borehole restrictions; as well as extra 6 days for running, cementing and clean-out. A novel engineered approach with Microfine cement slurry design squeezed into the damaged zone successfully regained casing and well integrity, while maintaining full borehole access through the production casing, thus saving rig time and tangible cost. Well drilling operations should be carefully designed and executed targeting the integrity assurance by providing the right casing metallurgy and good cementation for proper zonal isolation behind individual casing strings to mitigate external casing corrosion and act as the first line of defense against corrosion and any potential leakage or cross flow among different formations across the life span of the well. Well completions should be installed / tested considering the protection of inner production casing / liner from getting in prolonged contact with wellbore fluids, to avoid excessive internal corrosion and achieve reservoir fluid containment across the life of the well. A proactive approach been raised to acquire production casing / liners corrosion logs across workover activities especially regarding old wells to enable the mapping and interpretation of casing wall thickness / corrosion progress along the well life. That approach could aid in predicting the condition of production strings before commencing planned workover activity; and thus justify the availability of back-up repair plan to maintain rig operations and avoid any unscheduled operational surprises and possible strategic production rate defer.
This project began when a 9-5/8" in 43.5 ppf production casing became inaccessible due to the existing cemented pipe inside, preventing further reservoir section exposure and necessitating a mechanical side-track meanwhile introducing the challenge of loosing one section and imposimg slim hole challenges. The size and weight of the double-casing made for challenging drilling, as did the eight very different formations, which were drilled. The side-track was accomplished in two steps, an 8½ in hole followed by a single long 6⅛ in section, rather than the three steps (16 in, 12¼ in, 8½ in) that are typically required. The optimal kick off point carfully located across the dual casing by running electromagnetic diagnostics, the casing collar locator, and the cement bond log. The double casing mill was carefully tailored to successfully accomplish the exit in one run. Moreover, an extra 26 ft. MD rathole was drilled, which helped to eliminate the mud motor elongation run. A rotary steerable system was utilized directly in a directional BHA to drill an 8½ in open hole building section from vertical to a 30⁰ inclination. A 7.0 in liner was then set to isolate weak zones at the equivalent depth of the outer casing (13-3/8"). Subsequently, a single 6⅛ in section was drilled to the well TD through the lower eight formations. Drilling a 6⅛ in section through eight formations came with a variety of challenges. These formations have different challenging behaviors relative to the wellbore pressure that typically leads to the drilling being done in two sections. Modeling the geo-mechanical characteristics of each formation allowed the determination of a mud weight range and rheology that would stabilize the wellbore through all eight formations. The slim, 6⅛ in, hole was stabilized with higher equivalent circulating density (ECD) values than is typically used in larger boreholes. Optimizing mud weight and drilling parameters, while managing differential sticking with close monitoring of real-time ECD, helped to stabilize the high-pressurized zones to deliver the well to the desired TD with a single borehole. This project represents the first time in Kuwait that double casings in such large sizes have been cut and sidetracked. It is also the first time these eight formations have been cut across such a smaller hole size, slim hole (6⅛ in) in a single shot. Geo-mechanical modeling allowed us to stabilize the pressurized formations and to control the ECD. The well also deployed the longest production liner in the field commingling multiple reservoirs with differnt pore pressure ramps, with excellent cement quality providing optimal zonal isolation.
This paper describes the application of a combined answer from Electromagnetic and Ultrasonic imaging measurements to assess the well integrity prior to well side track and Whip-Stock setting. This solution was applied in a very old well in Raudhatain field in Kuwait that was completed since 1959. To optimize the cut depth for the side track across the single string, it was essential to identify an accurate depth of the external casing shoe, in addition to evaluation of both internal and external casings integrity and the cement bond quality for zonal isolation assurance. Data was acquired in September 2015 where the Electromagnetic log along with Ultrasonic images have been utilized with the advantage to provide answer in sections completed with dual strings for well integrity assessment. The log results could detect the external casing shoe at the depth 7170-ft, presented good pipe integrity for the internal casing, and indicated good pipe condition with minor metal loss in the external casing across the double strings interval. The measured outer casing shoe was found 21-ft deeper than the theoretical from the old well sketch data, hence the depth of the well side track and Whip-Stock setting were optimized accordingly. Failing to confirm the actual depth of the external casing shoe could have unintentionally led into drilling the side track across the double casing section resulting in undesirable workover operations and rig cost. Drilling a side track in dual pipe completed interval would also result-in damaging the outer casing and high remedial cost that cannot be predicted. The operator "Kuwait Oil Company" has achieved their objective to side-track the well across single casing string without taking any risk and avoiding any implications through wireline technology and solutions.
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