--> Well Placement Matters: Improving Survey Accuracy by Using Continuous Directional Data and Drilling Parameter Settings

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Well Placement Matters: Improving Survey Accuracy by Using Continuous Directional Data and Drilling Parameter Settings

Abstract

Traditional directional surveys used in the determining wellbore position are based on a minimum-curvature calculation method. This method assumes that a constant smooth curve exists between each of the stationary directional survey points, and is the current standard industry-wide. However, it is outdated since it totally ignores modern continuous survey measurements and/or any directional drilling parameters changes made between the stationary survey points. Previously published papers, have discussed the value of the continuous survey data to identify instances that occur while drilling in which the minimum curvature assumption is invalid and results in gross positional errors. Further, it was shown how these can lead to the accumulation of significant TVD and positional error. However, these papers fall short in providing a methodology for combining this data into a final industry accepted definitive positional survey. The authors propose a new method, the Continuous Directional Enhancement Method (CDEM), which combines the available continuous directional survey measurements and steering parameter setting changes with the stationary survey data to create a new hybrid and more accurate survey. When CDEM is used in real-time by geologists and geosteerers, it can result in optimally landed wells in the correct lobe and/or relative to fluid or gas contacts. The method also greatly aids in the proactive steering of the lateral section of horizontal wells within the target zone. As part of the methodology, the continuous survey data streams are collected and filtered in real-time to remove noise and to determine directional tendencies. This may include both near-bit and continuous MWD inclination and sometimes azimuth data. By adding the directional steering parameters, such as gravity tool-face and steering force (when running Rotary Steerable Systems), it is possible to predict the inclination and azimuth at the bit and on an ongoing bases provide a real-time trajectory to the bit. Additionally, the CDEM method provides for a constant monitoring of directional drilling tendencies and is used to identify changes in tendencies that result from directional parameter setting changes and/or from changes in lithology. In several instances, severe deflections where identified early, which exceeded the recommended maximum doglegs severity for rotating the MWD/LWD tool through and drilling was stop in order to evaluate the potential risk to cause a tool failure. In several cases, it was decided to back up and sidetrack rather than drill ahead. Overall, the CDEM adds value and understanding across disciplines, providing for better communication between drilling and geology. Also it enables accurate well placement, more accurate dip calculations, a better understanding of borehole tortuosity and torque and drag - all leading to significant increase in NPV. In this paper, we will fully describe the CDEM methodology and workflow, presenting several case history examples of the successful application in the placement of multiple horizontal wells.