4) Circulation gas

Is the gas being liberated into the borehole when actual “hole making” is stopped and the mud is circulated with the bit on bottom. The purpose of this practice is to get an idea of the degree of underbalanced at that particular depth internal.

• Miscellaneous gases:

Kelly gas

Results from air trapped in the drill string during a connection. It can be easily identified by the time of its appearance relative to the time of connection and the pump rate to get this gas down the drill pipe up the annulus.

Carbide gas

Is caused by the mud logger putting a specified amount of carbide in a dissolvable package into the drill pipe at the time a connection is made. This carbide reacts with the mud and creates an acetylene that is a check for the time required to pump cuttings off bottom to the surface; lag check.

39. Gas detection and analysis monitoring equipment

• Gas Trap Assembly

Continuously operating explosion proof, electrically powered degasser for breaking-out entrapped gases from mud.

• Total Gas Detector

Computer interfaced flame ionization detector which analysis a continuous stream of gas and air drawn from the gas trap, for total hydrocarbon gases. Accuracy to 1 unit (0.03%).

• Gas chromatograph

Computer interfaced, programmable flame ionization baseline chromatorgaph with automatic sampling and calibration for detection of hydrocarbons gas components, C1, C2, C3,C4, iso & normal, and C5.

Samples are either taken from the gas trap or by manual injection from the steam still.

• steam still

It is an equipment used to measure the hydrocarbon gas dissolved in mud. A fresh mud sample is injected into a chamber and steam is used to elaborate the contained gas from mud. This is then sucked out using a special syringe and injected into the chromatograph for the analysis.

The gas systems are calibrated using minimix test gases containing C1 - C5 hydrocarbons and are checked regularly. The H2S sensors can also be checked using ampoules or low concentrations and any necessary adjustments is made.

Gas trap assembly

The Baroid mud gas trap is an electric motor driven device giving a combination function of agitator and fluid pump power is supplied to the motor from the logging unit through the 110V distribution system. The motor drives an impeller enclosed within the stainless trap chamber which is immersed in the flowline mud flow. The mud enters the trap body through a variable diameter opening in the base of the chamber where it is agitated into a vortex by the impeller. The vortex throws the mud upwards on the inside wall of the chamber and liberates any entrained gases through the action of the vortex, and the agitating effect of the impeller. The mud exits through an opening in the side of the trap chamber. The gas and air mixture is drawn-off through the top of the chamber at 6 CFH (Cubic Feet/Hour) and drawn through a series of moisture and dust filters prior to being distributed in the detector, the chromatograph and the CO₂ detector.