The objective is to increase the production/injection rate of the existing old sick vertical wells that are completed with 7" casing, by extending the reservoir exposure with converting those wells to horizontal producer/injector. In the initial Field Development stage, many wells were drilled and completed with 7" casing up to the surface. Several of those old wells are lying inactive in North Kuwait which has one of the largest oil reservoirs in the country. In addition, of the limited surface locations in the field combined with the growing anti-collision challenges, feasibility studies were carried out for reviving such sick wells which can't be delivered via limited hole sections; accordingly, an innovative idea introduced to complete those wells with 3 7/8" or 4 1/8" Open Hole Completion. To address the required challenges, 2-7/8" PAC HT DP had been used along with 3 1/8" Motor. Consequently, DP had to be spaced out every trip to maximize the WOB transfer and mitigate Buckling issues. This paper provides an overview of 3 7/8" slim horizontal hole by taking the challenge to the next level by drilling the longest 3 7/8" horizontal slim hole in the world with a total footage of 4,565 ft. Total 7-runs had been performed to achieve this lateral length due to the limitation of BHA/LWD Battery life. Thirteen such wells have already been drilled consisting of 7 Injectors and 6 Producers. The Slim Wells are completed as an Injector with 5" seal assembly along with 4 ½" Tubing, or as a Producer with 3 ½" tubing and ESP. All wells (both Injectors and Producers) have yielded results commensurate to the potential of any new conventional horizontal well. Consequently, Slim Hole Horizontal wells were successfully drilled in Kuwait Oil Company fields. As such, the campaign of reviving the sick wells helped KOC to achieve higher return on investment in mature assets through minimizing top hole construction cost and time. The success has opened up new avenues for KOC. Re-entry wells helped to achieve higher return on investment in mature assets through minimizing top hole construction cost and have been drilled at 1/3rd the cost of a new well. It also accelerates time to oil production from existing wells and has minimized the prevailing location constraints. KOC has launched an aggressive plan to complete more such sick wells.

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.

The execution of pinpointed multi-stage acid fracturing inside 4-1/8-in. slim horizontal open hole sections is discussed. For the first time in Kuwait, pinpoint stimulation of 16 frac stages across a total 4,666 ft open hole while commingling three reservoir sections in very low reservoir quality carbonate rock was performed. Pumping rates were optimized while managing differential sticking hazards in the implementation of this frac procedure. Electric submersible pump completion deployment and well testing enhanced production by more than 100% over the anticipated rate. Stimulation parameters were optimized with 2-7/8-in. tubing as the frac string for greater reservoir penetration and productivity enhancement. Differential sticking was addressed by removing drilling filter cake prior to the frac job. Possible risks were evaluated, and mitigation plans were implemented which resulted in the successful application of multi-stage acid fracturing across the open hole.

A mechanical earth model was constructed for an oilfield in Kuwait that has a history of borehole related problems and prone to significant non-productive time in the highly deviated wells, the typical sidetrack wells took more than 100% of the time compared to the low deviated wells. The field is geologically complex, tectonically stressed with faults, fractures, unstable shales and anomalous pore pressures. Wells drilled within the structure are highly deviated with trajectories that almost parallel reservoir bedding planes, and that are aligned with the direction of minimum geomechanical stress. A comprehensive study was conducted to better understand the stability issues and to investigate the feasibility of drilling numerous additional high deviation wells. Data from selected offset wells was collated, analyzed and combined with field and regional information to construct a geological model which could then be used to predict and mitigate drilling related problems. The equivalent mud weight is arguably the most critical drilling variable and an element of the new plan would take account of stress dynamics and formation strengths to develop a mud program for vertical and horizontal sections. A geological model was developed using data from offset wells combined with field and regional knowledge. Well logs, mud logs and operational reports were analyzed, while unstable zones and failure mechanisms identified and incorporated into the earth model. A well plan was developed which included a comprehensive mud program and operational contingency actions for unplanned events. The planned well was drilled and monitored in real time, with emphasis on mud weight and mud rheology through the unstable and reactive shales. Multiple failure mechanisms such as stress induced wellbore instability, invasion of drilling fluids into weak bedding / micro-fractures and osmotic sensitivity, were found to be the root cause of wellbore instability across reactive shale formations especially during drilling of highly deviated wells. Correct mud weight and type prediction was one key factor during the drilling stage to keep the wellbore stable and deliver good borehole geometry, including the water phase salinity and fluid properties. The key objectives of the study were to define a safe MW program for the vertical and deviated sections of the planned well by conducting a wellbore stability study and to determine a real-time strategy to mitigate or manage wellbore instability problems as they arise. The paper describes the process of optimizing drilling practices and the application of real-time geomechanical monitoring for successful drilling. This application promises to open the prospect of drilling additional complex trajectory well while mitigating against non-productive time.

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