Time-Based to Depth-Based Data Conversion Engine

1. Reconciling Time-Series Telemetry with Subsurface Depth

Surface logging units and downhole MWD/LWD tools continuously record sensor parameters (e.g., Weight on Bit, Rotary Speed, Torque, Standpipe Pressure, Rate of Penetration, and Mud Gas) chronologically as a function of Time (UTC). In contrast, geoscientists, petrophysicists, and reservoir engineers evaluate rock formations strictly as a function of Depth along the wellbore trajectory.

Converting chronological sensor data into geological depth logs is a complex challenge. During drilling operations, the drill string spends substantial time off-bottom—such as during pipe connections, reaming, wiper trips, and circulation intervals—where sensors continue logging while depth remains constant. The WDA Time-to-Depth Conversion Engine (accessed directly from the Databases Explorer tree by right-clicking any Channelset and selecting Convert to Depth Data...) discriminates true on-bottom cutting footage from stationary or off-bottom operations, resampling telemetry into uniform depth-indexed log tables.

2. On-Bottom Drilling Discrimination & Resampling

To prevent stationary depth smearing and eliminate artificial data clustering, the conversion engine reconciles two fundamental wellbore depth coordinates:

• Hole Depth (DEPTMEAS): The maximum total drilled measured depth reached by the borehole to date.
• Bit Depth (DEPTBITM): The instantaneous positional coordinate of the drill bit cutting face along the borehole.

During active on-bottom penetration, Bit Depth progresses in lockstep with Hole Depth. WDA enforces an adjustable On-Bottom Tolerance Threshold:

Any sensor row where the bit is retracted off-bottom beyond the tolerance margin is automatically excluded from the depth-resampling grid. This ensures that only genuine rock-cutting parameters and newly exposed formation responses are mapped to the final petrophysical profile.

3. Mathematical Interpolation & Configuration Controls

Because physical sensor telemetry packets are logged at discrete time timestamps that rarely match exact round depth numbers, WDA applies continuous linear interpolation across bounding time samples:

• Uniform Depth Step (Increment):

  Define the target resolution of the generated depth series (typically 0.1 m or 0.5 ft). WDA projects continuous channels onto exact uniform depth increments, creating clean, regularly sampled logs ideal for automated petrophysical modeling and wireline overlay.

• Anti-Aliasing Linear Interpolation:

  For continuous physical variables (e.g. Gamma Ray, Resistivity, Sonic Transit Time, ROP), the algorithm calculates values at target depth $D_{\text{target}}$ by interpolating between consecutive bounding time records:
  Value(D_target) = V1 + ((D_target - D1) / (D2 - D1)) * (V2 - V1)

• Discrete Flag Handling:

  Categorical lithology codes, bit indicators, and operational flags utilize nearest-neighbor assignment to prevent fractional mathematical distortions.

• Overwrite Management:

  Easily toggle whether to replace previously converted depth records or append newly drilled intervals as operations proceed.

4. Step-by-Step Conversion Workflow

1. Open the Conversion Engine: In the Databases Explorer tree, right-click any time-indexed Channelset and select Convert to Depth Data....
2. Configure Parameters: Specify your target Depth Step (e.g., 0.1 m) and On-Bottom Tolerance (e.g., 0.2 m).
3. Launch Resampling: Click Start Conversion. WDA's multithreaded calculation engine processes hundreds of thousands of sensor rows in the background.
4. Monitor Execution: The live UI displays elapsed time, total generated depth rows inserted into the depth-indexed log table, and a progress bar.
5. Inspect Converted Logs: Right-click the channelset and select Analyze Depth Data to launch the Depth Analysis Console, or export the resulting curves via the Data Export Console.

5. Related WDA Engineering Modules

• WDA: WITSML Compatible Data Analyzer: Discover WDA's columnar architecture and high-performance charting.
• Time-Based Analysis Console: Analyze raw chronological telemetry and drilling dynamics prior to depth resampling.
• Depth-Based Log Analysis & Petrophysics: Display the converted depth data in standard inverted vertical tracks with lithology and porosity shading.