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High-fidelity trajectory estimation combined with dual-probe Measurement-While-Drilling (MWD) directional instrumentation provides a solution to minimum curvature’s known inefficiencies in modeling the true wellbore position and definition (Stockhausen & Lesso, 2003). While it may not be cost efficient to increase survey frequency from the industry standard of 30ft-200ft, it is possible using the techniques defined in this research to maintain current survey intervals and increase wellbore placement accuracy while reducing positional uncertainty by up to 45% over the most advanced commercially available magnetic survey correction algorithms. Taking advantage of modern MWD tool platforms enables the installation of an additional (30-inch) survey measurement probe in the existing tool string with a fixed and known offset to the primary survey probe. Directional surveys from both survey probes are telemetered to surface at traditional course length survey intervals in real-time. The two surveys along with the known steering and non-steering intervals are processed through a high-fidelity trajectory estimation algorithm to quantify the wellbore behavior between survey stations. The result is a highly accurate and dense survey listing with modeled trajectory waypoints between traditional surveys to reduce the course length between directional measurement datapoints and better capture the true well path. Through extensive lab modeling, it was determined that the use of the dual-probe MWD package in combination with the high-fidelity trajectory estimation algorithm could result in a reduction in the Ellipse of Uncertainty (EOU) by 20% in the horizontal (semi-major) plane and 45% in the vertical (semi-minor) plane when compared to Multi-Station Analysis (MSA) and BHA Sag survey correction techniques. In addition to proof-of-concept modeling, the system has been deployed and used in real-time application on three separate pads, totaling nine wells. The results were able to validate and exceed baseline goals by exhibiting, on average, a reduction of the EOU by 21% in the horizontal plane and 58% in the vertical plane. Further, True Vertical Depth (TVD) error at well Total Depth (TD) in excess of 10ft was observed on three out of nine wells (33%) in this limited real-time application study. This difference was relative to separate, concurrent processing of the surveys via Multi-Station Analysis (MSA) and BHA sag corrections. This level of increased TVD accuracy is significant in many applications, depending on zone thickness and difficulty of geological interpretation. Increased accuracy and reduced uncertainty result from a better understanding of the true well path between traditional course length surveys. The trajectory estimation algorithm quantifies the rotational build/drop and walk rates in real-time and is reinforced by the dual-probe directional survey measurements. These tendencies can be used to better project forward to the bit as the well is drilled. Improved projection to the bit allows for enhanced recognition of deviation from the well plan and better-informed steering decisions.
High-fidelity trajectory estimation combined with dual-probe Measurement-While-Drilling (MWD) directional instrumentation provides a solution to minimum curvature’s known inefficiencies in modeling the true wellbore position and definition (Stockhausen & Lesso, 2003). While it may not be cost efficient to increase survey frequency from the industry standard of 30ft-200ft, it is possible using the techniques defined in this research to maintain current survey intervals and increase wellbore placement accuracy while reducing positional uncertainty by up to 45% over the most advanced commercially available magnetic survey correction algorithms. Taking advantage of modern MWD tool platforms enables the installation of an additional (30-inch) survey measurement probe in the existing tool string with a fixed and known offset to the primary survey probe. Directional surveys from both survey probes are telemetered to surface at traditional course length survey intervals in real-time. The two surveys along with the known steering and non-steering intervals are processed through a high-fidelity trajectory estimation algorithm to quantify the wellbore behavior between survey stations. The result is a highly accurate and dense survey listing with modeled trajectory waypoints between traditional surveys to reduce the course length between directional measurement datapoints and better capture the true well path. Through extensive lab modeling, it was determined that the use of the dual-probe MWD package in combination with the high-fidelity trajectory estimation algorithm could result in a reduction in the Ellipse of Uncertainty (EOU) by 20% in the horizontal (semi-major) plane and 45% in the vertical (semi-minor) plane when compared to Multi-Station Analysis (MSA) and BHA Sag survey correction techniques. In addition to proof-of-concept modeling, the system has been deployed and used in real-time application on three separate pads, totaling nine wells. The results were able to validate and exceed baseline goals by exhibiting, on average, a reduction of the EOU by 21% in the horizontal plane and 58% in the vertical plane. Further, True Vertical Depth (TVD) error at well Total Depth (TD) in excess of 10ft was observed on three out of nine wells (33%) in this limited real-time application study. This difference was relative to separate, concurrent processing of the surveys via Multi-Station Analysis (MSA) and BHA sag corrections. This level of increased TVD accuracy is significant in many applications, depending on zone thickness and difficulty of geological interpretation. Increased accuracy and reduced uncertainty result from a better understanding of the true well path between traditional course length surveys. The trajectory estimation algorithm quantifies the rotational build/drop and walk rates in real-time and is reinforced by the dual-probe directional survey measurements. These tendencies can be used to better project forward to the bit as the well is drilled. Improved projection to the bit allows for enhanced recognition of deviation from the well plan and better-informed steering decisions.
It is known that the Stockhausen Effect, characterized as the accumulation of TVD error in directional wellbores resulting from the slide/rotate process employed with bent-housing mud motors, can have a significant impact on wellbore placement in the TVD plane. While much research has been conducted, and commercial solutions have been deployed to account for and correct these errors, all are focused on mud motor slide/rotate drilling. As contemporary drilling programs move to ever-increasing lateral lengths, utilization of Rotary Steerable Systems (RSS) is also trending upward. While potential advantages may exist in favor of RSS, like the elimination of slide drilling, it is important to consider that not all undesirable phenomena associated with slide drilling (well placement error, tortuosity, rugosity, high localized DLS, etc.) vanish from the wellbore. These characteristics are still present in the RSS wellbore and should be analyzed and quantified to ensure that wellbore quality metrics are consistent for all drilling methods. To investigate cumulative TVD error in RSS wells, we developed a system to utilize the real time downhole steering data from RSS to populate a steering sheet that can be processed through an algorithm designed to account for TVD errors resulting from the Stockhausen effect. By capturing the RSS toolface and steering proportion in real time, we can determine at what intervals the RSS is actively steering and during what intervals it is drilling in a neutral, non-biasing mode. The result of cycling between steering and non-steering cycles creates a pattern similar to a slide/rotate sequence experienced when using steerable mud motors. This information allows us to construct a more accurate representation of the true trajectory of the wellbore than is provided by minimum curvature between the standard 95’ survey course lengths. In addition to uncovering TVD error this method also provides a higher resolution picture of various tortuosity metrics like borehole curvature and torsion. We examined data from numerous wells across several basins to observe the TVD error generated by RSS steering mechanisms. It was concluded that these TVD errors should be considered for accurate wellbore positioning, and in addition revealed potential to enhance trajectory optimization capabilities of some Rotary Steerable Systems. In addition to uncovering TVD error, the high-resolution trajectory allows for a thorough examination of wellbore tortuosity, including localized DLS, and wellbore curvature and torsion to aid in identifying potential trouble zones in the lateral.
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