Carbide Lag Section

Daily Geology Report

The Carbide Lag section captures data on carbide inserted in the hole to determine hole gauge.

This section contains a Detail spreadsheet to record carbide data. For information on using spreadsheets, see the Using Spreadsheets and Tables topic.

Tritium

Tritium is a heavy isotope of hydrogen 3H that is typically used as a tracer to age date water samples (e.g., seawater, groundwater to detect circulation or admixing of fluid in a reservoir or aquifer). Record a Tritium profile over the drilled interval.

Carbide Lag and Details Areas

The Carbide Lag and Details areas are used to record carbide bomb dropped to determine average hole size of the current open hole section. Carbide bombs are dropped inside the drill pipe from the rig floor while making a connection. The carbide reacts with water-based drilling fluid to release acetylene gas which is pumped down the drill pipe and circulated back up the annulus to the return flow line. The gas peak is measured by the Total Gas Detector and enables the average diameter of the current open hole section to be determined using the pump strokes measured before the returned acetylene gas is measured at surface. Measured pump strokes is converted to pumped volume using the pump output. Using the pipe depth, inside diameter and outside diameter, the volume of the open hole section (using MD at connection) is converted into an average hole size. This average hole size can then be used by the mud loggers and/or wellsite geologist to lag drill cuttings more accurately, compared to just using the bit size. In practice, the mud loggers can just use the additional strokes required to circulate the acetylene gas compared to theoretical (calculated) strokes and add these when lagging cuttings samples back to surface.

Lag Time

Lag time is converted from total up and down pump strokes for when the carbide gas is measured at surface.

Carbide bomb is inserted into drillstring at surface and pumped down the string and back up the annulus.

You can use Strokes to calculate fluid volume using the pump output (volume/stroke). If the hole is in gauge, the carbide time (strokes) should equal the calculated or theoretical lag time (strokes). If the carbide time is greater than the theoretical lag time, then the hole is out of gauge (larger than bit). If the carbide time is less than the theoretical lag time, the average hole size is under-gauge (smaller than the bit). Actual Strokes - Calc Strokes = Extra Strokes (may be positive or negative) Extra Strokes * Vol/Stroke = Extra Volume. Extra Volume can be converted back to Hole Size using length of Open Hole (Carbide Depth - Casing Shoe depth)

Carbide Lag Strokes Actual

Enter the actual carbide lag strokes.

Carbide Lag Strokes Calc

Enter the calculated lag strokes assuming in gauge hole.