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Appropriate selection of a bottom-hole assembly (BHA) is critical to the success of a drilling operation. In US Land drilling, these assemblies are often selected using local heuristics rather than rigorous analysis. These heuristics are frequently derived from the incentives of the directional contractor as opposed to incentives for the operator. Large motor bends enable more rotation though the curve and reduce the possibility of tripping for build rates. Unstabilized motors are believed to aid sliding and tool face control. Both of these practices lead to drilling a more tortuous wellbore and may cause problems later in the well’s life. This study quantifies the impact of these practices and proposes alternatives that can balance the needs of directional companies with the desire of operators for high-quality wellbores. Over 60 conventional motor assemblies used to drill curves in the Eagle Ford and Permian were analyzed for directional performance using commercial drillstring analysis software. The sliding and rotary tendencies were modelled through the curve across a range of potential drilling conditions. Expected build-rate models were validated by comparison to the maximum achieved doglegs in the directional surveys. When available, additional validation was performed using motor yields calculated from slide sheets. The validated models were compared to the dogleg severity requirements for each assembly’s respective well plan. Comparisons of slide ratios and slide/rotate tendencies of the BHAs were used to estimate the impact on wellbore quality using the tortuosity metric proposed by Jamieson (2019). Typical well plans for both basins had curves of 10 degrees/100ft with no well plan greater than 12 degrees/100ft. Typical bottom hole assemblies were capable of >15 degrees/100ft under normal sliding conditions, with some assemblies capable of >20 degrees/100ft of build. Predicted build rates were validated by slide sheets and observed dogleg severities. Common characteristics among assemblies with excess capacity were high bend angles (>=2 degrees) and minimal stabilization. These slick assemblies also had a strong drop tendency in rotation at low inclinations. The combination of high-build rate with rotary drop greatly increases tortuosity, particularly in the early stages of well. A minority of the assemblies used a lower motor bend angle (<2 degrees) combined with multiple stabilizers. These assemblies had a more consistent directional capability throughout the curve and held angle in rotation. The success of these assemblies confirms that a higher quality wellbore with an improved BHA design is technically achievable. As increasing attention is afforded to the topic of wellbore quality it is important to have methods available to technically achieve high-quality wellbores. In addition to the management of drilling practices, it is also important to have an appropriate BHA design that can enable those practices
Appropriate selection of a bottom-hole assembly (BHA) is critical to the success of a drilling operation. In US Land drilling, these assemblies are often selected using local heuristics rather than rigorous analysis. These heuristics are frequently derived from the incentives of the directional contractor as opposed to incentives for the operator. Large motor bends enable more rotation though the curve and reduce the possibility of tripping for build rates. Unstabilized motors are believed to aid sliding and tool face control. Both of these practices lead to drilling a more tortuous wellbore and may cause problems later in the well’s life. This study quantifies the impact of these practices and proposes alternatives that can balance the needs of directional companies with the desire of operators for high-quality wellbores. Over 60 conventional motor assemblies used to drill curves in the Eagle Ford and Permian were analyzed for directional performance using commercial drillstring analysis software. The sliding and rotary tendencies were modelled through the curve across a range of potential drilling conditions. Expected build-rate models were validated by comparison to the maximum achieved doglegs in the directional surveys. When available, additional validation was performed using motor yields calculated from slide sheets. The validated models were compared to the dogleg severity requirements for each assembly’s respective well plan. Comparisons of slide ratios and slide/rotate tendencies of the BHAs were used to estimate the impact on wellbore quality using the tortuosity metric proposed by Jamieson (2019). Typical well plans for both basins had curves of 10 degrees/100ft with no well plan greater than 12 degrees/100ft. Typical bottom hole assemblies were capable of >15 degrees/100ft under normal sliding conditions, with some assemblies capable of >20 degrees/100ft of build. Predicted build rates were validated by slide sheets and observed dogleg severities. Common characteristics among assemblies with excess capacity were high bend angles (>=2 degrees) and minimal stabilization. These slick assemblies also had a strong drop tendency in rotation at low inclinations. The combination of high-build rate with rotary drop greatly increases tortuosity, particularly in the early stages of well. A minority of the assemblies used a lower motor bend angle (<2 degrees) combined with multiple stabilizers. These assemblies had a more consistent directional capability throughout the curve and held angle in rotation. The success of these assemblies confirms that a higher quality wellbore with an improved BHA design is technically achievable. As increasing attention is afforded to the topic of wellbore quality it is important to have methods available to technically achieve high-quality wellbores. In addition to the management of drilling practices, it is also important to have an appropriate BHA design that can enable those practices
Summary Appropriate selection of a bottomhole assembly (BHA) is critical to the success of a drilling operation. In US land drilling, these assemblies are often selected using local heuristics rather than rigorous analysis. These heuristics are frequently derived from the incentives of the directional contractor as opposed to incentives for the operator. Large motor bends enable more rotation through the curve and reduce the possibility of tripping for build rates. Unstabilized motors are believed to aid sliding and tool face control. Both of these practices lead to drilling a more tortuous wellbore and may cause problems later in the well’s life. This study quantifies the impact of these practices and proposes alternatives that can balance the needs of directional companies with the desire of operators for high-quality wellbores. More than 60 conventional motor assemblies used to drill curves in the Eagle Ford and Permian basins were analyzed for directional performance using commercial drillstring analysis software. The sliding and rotary tendencies were modeled through the curve across a range of potential drilling conditions. Expected build-rate models were validated by comparison to the maximum achieved doglegs in the directional surveys. When available, additional validation was performed using motor yields calculated from slide sheets. The validated models were compared to the dogleg severity (DLS) requirements for each assembly’s respective well plan. Comparisons of slide ratios and slide/rotate tendencies of the BHAs were used to estimate the impact on wellbore quality using the tortuosity metric proposed by Jamieson (2019). Typical well plans for both basins had curves of 10° per 100 ft with no well plan greater than 12° per 100 ft. Typical BHAs were capable of >15° per 100 ft under normal sliding conditions, with some assemblies capable of >20° per 100 ft of build. Predicted build rates were validated by slide sheets and observed DLSs. Common characteristics among assemblies with excess capacity were high-bend angles (≥2°) and minimal stabilization. These understabilized assemblies exhibited unstable rotary tendencies across a range of drilling parameters. The combination of high-build rates with rotary drop masks the true level of tortuosity in a wellbore, leading to an underestimation of unwanted curvature. A minority of the assemblies used a lower motor bend angle (<2°) combined with multiple stabilizers. These assemblies had a more consistent directional capability throughout the curve and exhibited stable behavior in rotation. The success of these assemblies confirms that there is potential for tailoring BHA designs to improve wellbore quality without compromising the technical objectives of the well. As increasing attention is afforded to the topic of wellbore quality, it is important to have methods available to technically achieve high-quality wellbores. In addition to the management of drilling practices, it is also important to have an appropriate BHA design that can enable those practices.
With increasing numbers of unconventional horizontal wells on single pads and the desire to get deeper unconventional wells drilled to TD as economically as possible, higher well deviations and Dogleg Severities (DLSs) have posed challenges for Electrical Submersible Pump (ESP) conveyance. These challenges have led to situations where high bending stress during ESP conveyance has led to early ESP failure. To mitigate the potential for high bending stress during ESP conveyance, there has been: A renewed focus on drilling intermediate hole sections with low DLS, andWorkflow changes to obtain and analyze gyro surveys on wells following handover from Drilling before perf & frac operations. Summarized in the paper is a series of short run ESP failures in the Permian Basin that led to these new workflows for A/L selection and ESP conveyance planning. The study was initiated with a review of ESP teardown reports which revealed that most failures in the study area were not linked to high ESP bending stress during conveyance, but rather to Iron Sulfide (FeS) scaling within the ESPs. Nonetheless, Software was used to analyze and quantify ESP bending stress during conveyance for historical and future wells,A FeS scale inhibitor trial was initiated by adding chemical to the frac stages for some future ESP candidate wells, andApproximately 30 high resolution (1-ft) gyro surveys were collected in 5 ½" and 7" casing and processed at 1’, 15’, 25’ and 100’ intervals. Various metrics were calculated using the data, including wellbore DLS and Effective Rigid Pass-Through Diameter to highlight the advantage of gyros over traditional low resolution MWD surveys in wells where ESPs are planned.
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