Abstract: A method analyzes the hydrocarbon composition of geological strata. The method includes an analysis of gaseous hydrocarbon concentrations contained in drilling muds. According to the method, for a given depth range, gaseous hydrocarbon concentration ratios are established in pairs at essentially-identical depths. Subsequently, a sub-set of the ratios is selected in order to form a signature that is representative of the gaseous hydrocarbon composition of the depth range. The aforementioned signature is defined by the at least one straight line representing the concentration of a first gaseous hydrocarbon in relation to the concentration of a second hydrocarbon. The signature is then compared to reference signatures in order to determine the hydrocarbon concentration of the geological stratum corresponding to the depth range.

Abstract: A method includes the phases of measuring the quantity of a given gas in the gases extracted from a calibration sample of a calibration mud, in at least two stages for extraction under predetermined conditions. A family of curves representing the extraction, under the predetermined conditions, of the given gas from the drilling mud, is established on the basis of the measurements carried out. The method also includes the phases of measuring the quantity of given gas in the gases extracted from an analysis sample of the drilling mud in an extraction stage, under the predetermined conditions; and computing the given gas content of the drilling mud on the basis of the measured quantity of given gas and of a curve of the family.

Abstract: The invention relates to a method of analysing the hydrocarbon composition of geological strata, comprising an analysis of the gaseous hydrocarbon concentrations contained in the drilling muds.According to the invention, for a given depth range, gaseous hydrocarbon concentration ratios are established in pairs at essentially-identical depths. Subsequently, a sub-set of said ratios is selected in order to form a signature that is representative of the gaseous hydrocarbon composition of the depth range. The aforementioned signature is defined by at least one straight line representing the concentration of a first gaseous hydrocarbon in relation to the concentration of a second hydrocarbon. Said signature is then compared to reference signatures in order to determine the hydrocarbon concentration of the geological stratum corresponding to the depth range.

Abstract: The method includes the phases of measuring the quantity (q1, q2) of given gas in the gases extracted from a calibration sample of a calibration mud, in at least two stages for extraction under predetermined conditions; and establishing a family (310) of curves (303, 305, 309) representing the extraction, under the predetermined conditions, of the given gas from the drilling mud, on the basis of the measurements carried out. It also includes the phases of measuring the quantity (qd1) of given gas in the gases extracted from an analysis sample of the drilling mud in an extraction stage, under the predetermined conditions; and computing the given gas content of the drilling mud on the basis of the measured quantity (qd1) of given gas and of a curve (309) of said family (310).