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: 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: A method for the estimation of pore pressure within a subterranean formation containing fluid during the drilling of a bore hole. The bore hole is drilled using a drill string consisting of a drill bit fitted to its lower end, and using drilling mud pumped from the surface through the drill string and finally evacuated.

Abstract: The invention relates to a procedure for measuring the rate of penetration V.sub.F of a drill bit fixed to the lower end of a drill string lowered into a well. During an initial period, the well is drilled keeping, on average, the value of weight F of the drill string measured at the surface relatively constant, and the instantaneous values of the drill string rate of penetration V.sub.S and the weight F are measured at the surface at different successive moments. The value of the drill string average rate of penetration V.sub.SM at the surface is determined from the values of V.sub.S measured and the successive values of dF/dt of the first derivative with respect to time. The coefficient of apparent rigidity of the drill string during the initial period is then determined from the values of V.sub.SM, V.sub.S and dF/dt. Finally, the rate V.sub.F is calculated.

Abstract: In a method and apparatus for obtaining a recording of facies of geological formations, logging instruments are moved in a borehole to produce log measurements at successive levels of the borehole. With each level is associated a reference sample whose coordinates are constituted by the respective measurements in a multidimensional space defined by the different logs. The scatter of samples thus obtained is analyzed to distinguish modes characteristic of clusters in which the concentration of samples is the highest. The samples may then be associated with selected modes to form classes each characteristic of a respective facie, and the facies then displayed as a function of the depth of the respective associated sample.