A new pyrolysis instrument, developed by the Institut Francais du Petrole, and called "Rock-Eval" (see Espitalie, etal., OTC Paper 2935, 1977), has been successfully operated on the BenOceanLancer drill ship. As an integral part of a computer assisted mud logging unit, the device was used to rapidly identify and evaluate petroleum source beds during offshore drilling operations. The data allowed determination of the petroleum generating potential and the degree of maturation of the source rocks at the well site. It also provided a useful stratigraphic correlation tool. Advantages of applying this technique on the well site are:
better and more representative samples, leading to more accurate geochemical profiling,
instant access of the data to the well site geologist and exploration management, and
integration of geochemical data with conventional mud logging data during drilling operations.
This report describes the well site implementation and evaluation of the pyrolysis device. Because this instrument was designed for laboratory research, several significant problems had to be solved prior to use at the well site. Among these were: electrical problems specific to this device, weighing small samples (100 mg) at sea, and partial automation of the system to improve efficiency and precision. Extensive intercalibration checks with a land-based instrument were also conducted. Examples of data and applications to offshore exploration are given. The economics of operating the device offshore are favorable.
Organic geochemistry has become increasingly important to offshore oil exploration. As previously pointed out by Dow1, "Attention must be focused not only on traps and reservoirs, but on whether there is a reasonable expectation that they contain oil and gas before committing to expensive ventures in the largely unknown realm of continental slopes and rises." Source beds must be identified and an estimate made of their oil and gas potential and degree of maturation. When integrated with geophysical and geological data, this organic geochemical information can lead to identification of those segments of sedimentary basins where oil and/or gas have been generated in the subsurface.
Conventional geochemical profiling of wells requires carefully selected samples from drill cutings, sidewall cores, and conventional cores which are shipped to land-based laboratories for detailed analysis. Final delivery of data to users commonly follows weeks, if not months, later.
This report describes a joint project by Chevron Oil Field Research Company, Chevron Overseas Petroleum, Inc., and Exploration Logging, Inc., to evaluate the use of a new analytical device to rapidly screen large numbers of samples for geochemical data at the well site. Valuable information regarding the presence of source beds, the stratigraphy of organic matter, and the significance of hydrocarbon shows was made available at the same time as mud logs and electric logs.
