Interpretation of petrophysical well logs plays a major role in the analysis of geothermal and hydrocarbon reservoirs. The interpretation encompasses determination of lithology, porosity, permeability and hydrocarbon saturation of the drilled section.
Detailed lithological information and precise determination of reservoir properties are obtained from cuttings, cores and side-wall cores. However, the number and length of cored intervals are generally restricted and reservoir properties cannot be obtained from cuttings. Thus, determination of lithology and reservoir properties in the vast majority of wells rely on interpreting the data stored in a wide range of petrophysical well logs.
Lithology is primarily determined from the gamma-ray (GR) log combined with neutron (NPHI) and density (RHOB) logs. The GR, NPHI and RHOB logs form the basis of interpreting the effective porosity (PHIE) of sandstone and limestone layers. If hydrocarbons are present, the oil and/or gas saturation can be interpreted by adding data from the deep resistivity (ILD/LLD) log.
Prediction of reservoir quality may be optimised by combining log interpretation with core analysis, petrography and diagenesis data of reservoir sections. A synthetic permeability log may be derived from the combination of PHIE and core analysis data (porosity and permeability) providing a robust model of reservoir performance. In geothermal research, the transmissivity of reservoir sections can be estimated.
GEUS has several years of experience in interpreting well logs from both hydrocarbon and geothermal reservoirs. The log interpretation results may be integrated into modelling work and multidisciplinary studies. Our customers include oil companies, state institutions, local energy companies, etc. and we participate in comprehensive research projects with national as well as international educational and research institutions.