Quality Control with 4D Nav s QCView Software. Rig Move QA/QC Operations Using QCView. Case Study 1: Drillship Rig Move

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1 Quality Control with 4D Nav s QCView Software 4D Nav has introduced a software package designed to provide advanced QC capabilities for offshore operations. This paper describes some of the capabilities and provides case studies. Rig Move QA/QC Operations Using QCView Currently 4D Nav s QCView is used by multiple clients for rig move QA/QC operations. The software provides the client with the tools necessary to determine the quality of the rig s position in parallel but independently of the contractor. With traditional QC the client often has little raw data to base approval of the preliminary and final topside positions of a well on. With QCView, they are able to accept raw data from the contractor in real-time enabling them to verify critical components such as project geodesy, sensor offsets, rig offsets, DGPS data quality, heading data quality, as well overall movement of the rig. QCView operates as an independent navigation and QC suite under complete control of the client. The following highlights the key features that make this a valuable tool for reducing costs and identifying positioning issues and inefficiencies: 1. Project creation and planning. Enables the client to create their own database in the software before it is sent offshore, allowing internal checks for geodetics, DTM, project drawings, as well proposed coordinates. 2. EPSG Geodesy database. Simplifies checks of contractor s geodesy configuration. 3. Real-time data input. Input of raw position and heading data facilitates identifying dimensional and offset errors as well as enabling monitoring of vessel movement during operations. 4. Scene creation. Option to create a digital terrain model (DTM) from bathymetry data and populate it with seafloor assets such as wells, manifolds, PLETs, flowlines, etc. improves visualizing and comprehending the spatial relationship of working assets within the existing environment in real-time. 5. Real-time catenary modeling. Real-time catenary modeling of anchor lines, both simple and complex, during rig move operations. 6. Data logging. Comprehensive configurable data logging, including all sensors and processed vessel positions, to databases independent of contractor ensures all data required for analysis and playback is captured. 7. RINEX logging utility. Supports logging of raw GPS data to be collected for the DGPS antennas for further verification by client of positional integrity. 8. Remote monitoring. Using 4D Nav s network services, QCView can be monitored by a QCView client with network access. Case Study 1: Drillship Rig Move Figure 1 illustrates QCView features and displays used for a project to monitor operations from the offshore client office as well from the beach using QCView s remote monitoring capability. For this project the following were logged; raw position and heading sensor data; positions determined in QCView from the application of client-supplied offsets and; the survey contractor s final GGA position. These were then analyzed to determine if any issues in position quality, geodetics, offsets, or heading CO values existed. Upon analysis, the raw heading data logged showed a heading drift in the primary gyro

2 that was outside the specified tolerances and adjustments were made to use the backup-heading source to move the rig on to location. QCView s Average Positon Fix feature was used with the QCView determined position of the rig s topside well bore location and the results compared to the survey contractor s results. Little to no difference was noted between the two thus ensuring the quality of the topside well bore position. Figure 1 QCView Utilized for Position Monitoring as Rig is Moving into Position Case Study 2: Jack Up Rig Move into Platform A project for a client involving a jack-up rig with anchor moorings moving into an existing platform was conducted with QCView used to monitor operations. Precise determination of the rig s position was required due to minimal room for error on the approach and final position next to the platform. The use of QCView dramatically increased the confidence of the operators by introducing capabilities not provided by the survey contractor at the time. These included real-time catenary modeling of the anchor lines which enabled monitoring their spatial relationship to existing infrastructure and the 3D visualization of the rig during the its move into its final position. During this project, a position discrepancy was noted in the contractor s final GGA position after performing the geodesy checks and initial RINEX data verifications with QCView. The cause was determined to be due to the contractor having the ITRF output selected in their navigation suite instead of the correct geodetic output for the final position solution of the main rotary table, resulting in a position error. This was easily identified and corrected in a timely manner resulting in a successful completion of the rig move and final well positioning.

3 Figure 2 QCView Showing Catenaries Real Time with Mid-Line Bouncy Over Existing Infrastructure Array Planning/Validation Using QCView 4D Nav s QCView for array planning and validation of array data has been part of the standard operating procedures for many operators and end clients throughout the industry for several years now. The processing and QC of array data is crucial for accurate positioning of assets. Many factors play a role in determining the quality of an array and too often these are misunderstood or overlooked resulting in positioning errors, which are not always detected until the post mission review. QCView provides the tools to review and analyze arrays starting from the conception of a project and proceeding through execution to the final product minimizing the potential for issues to go undetected. QCView allows the client to plan an array accounting for seabed bathymetry and shadowing from existing infrastructure. This can also be used to evaluate a contractor s proposed array design. The program provides 2D and 3D visualizations showing the bathymetry, structures and any other pertinent features with the acoustic signal paths given the transponder locations and heights above the seafloor enabling the determination potential for blocked paths and multipath. Once the project is in the execution phase, the user can import the raw time-of-flight and turn-around data (e.g. Fusion s.mdb files) and sound velocity profiles and perform an independent array adjustment. QCView supports 2D and 3D network adjustments and provides complete statistics with the results. Comparing the QCView results with those of the contractor assists identifying any issues that may exist and determining the reliability and accuracy of the array. Figure 3 shows the visualization of an array, DTM and existing infrastructure used to determine the reliability of coverage at a drill center. In this instance, it is used to help determine any acoustic shadowing from existing infrastructure when tracking an ROV with LBL amongst the assets.

4 Figure 3 QCView Array Planning for Determining Possible Structure Shadowing Importing range data exported from the contractor s system enables review of the sound velocity used for the individual ranges during the contractor s data collection, repeatability of ranges and comparison of forward and reverse observations, among other items. Figure 4 shows a summary of a set of ranges imported into QCView presented in table format and a histogram color-coded for forward and reverse observations. This supports review of the data as used by the contractor as well as editing of the data for processing with QCView. It is important to note that the data can also be manually entered. Figure 4 Range Data Import Showing Range Statistical Data

5 One of the largest sources of error for any array is the sound velocity. Is the sound velocity used correct? Is the sensor measuring the sound velocity profile faulty? Is there an environmental change causing a fluctuation in sound velocity? Too often incorrect sound velocities have caused a poor array adjustment and subsequently, incorrect positioning of assets with the array and the data and the sound velocity data itself isn t captured effectively to allow for further data analysis. QCView enables multiple options for evaluating and validating sound velocity data. The user can import multiple sound velocity profiles as well as accept real-time sound velocity data. The sound velocity profile to be used for a data set can be selected or a specific sound velocity for an individual or group of ranges can be entered. This is useful when using current range data with legacy range data to determine the validity of an array over time. Figure 5 Sound Velocity QC Checks for Overall SVP as well SV Used at Depth The user can run mutiple scenarios for the of analysis of an array, using the raw data input to QCView for quality checks to determine the overall integrity of the array with estimated positioning error. Stations can be set to fixed, floating or contrained to help determine areas of uncertaintly. In addition, bearing constraints can be applied to prevent the array from rotating the overall soultion.

6 Figure 6 Array Data Interpretation and Validation

7 Comprehensive presentations of the data, as shown I Figures 6 and 7, allow the user to see the range data in relation to assets. In addition, ranges can be selected directly from the 2D navigation display for review. The navigation display will show which ranges are used, not used, the adjusted positions of station, as well the overall status of an array. Case Study 3: Combining Arrays A project 4D Nav assisted a client with involved combining two exisitng arrays, both of which had previously been calibrated at different times. One of the arrays showd little movement from the original data, validating the array to be within specified tolerances. The second array s original data indicated a poor overall solution, the cause of which needed to be identified. QCView enabled the addition of new range data to the original data to assist in determining possible sources of the error. It was determined that an incorect sound velocity was used for the original array adjustment. An incorrect ITRF transformation had also been applied the original array. Utilizing QCView s data archive and rigorous adjustment process the client was able to correct for the sound velocity and transformation errors resulting in a valid solution for the combined array. Figure 7 Array Overview in Navigation Screen