System for analysing gas from strata being drilled under high mud flows

摘要

A gas analysis system for determining the gas content of subterranean strata. A boring operation is commenced to form a borehole into or through a subterranean formation, such as a coal or shale formation to determine the gas content thereof. The drill fluid, cuttings and any desorbed gas is carried from the downhole location to surface analysing equipment in a closed system, so that the desorbed gases are not exposed to the air. The drill stem is capped or sealed at the surface, as well as the wellbore annulus to effectively seal the drill liquid, cuttings and desorbed gasses. The drill fluid, cuttings and desorbed gasses from the formation are coupled from the wellhead apparatus to the gas processing equipment via a closed system so that the constituents and volume of the gas can be determined.

主权项

1. A method of determining a gas volume per unit volume of subterranean borehole strata drilled by a drill pipe, and a non-coring drill bit of a known size connected at the bottom of the drill pipe, comprising:
drilling the borehole in a subterranean strata so that subterranean strata fluids do not flow into the borehole; monitoring drilling parameters with respect to time so that a position of the drill bit within the subterranean strata is known; monitoring a rate of a drilling liquid pumped down the drill pipe with respect to time, including periods of zero flow; capturing all of the drilling liquid, released gas and cuttings at a well head without air contamination and transferring the drilling liquid, released gas and cuttings to a separator; separating the gas and a mixture of drilling liquid and cuttings in the separator without air contamination; measuring a volume of the separated gas released from the separator with respect to time using a gas flow metering system, and measuring the volume of gas released from the separator without requiring interruption of drilling the borehole; returning the drilling liquid to a drilling fluid system for reuse by pumping down the drill pipe; carrying out a calculation based upon drill bit position, borehole size, drill pipe size and mud flow rate history to determine a location within the borehole from which the cuttings and the gas emanating therefrom are derived; and carrying out a calculation to determine a gas volume released per unit volume of borehole drilled at various borehole depts.