Reservoir geochemistry — A reservoir engineering perspective

This paper reviews the applications of reservoir geochemistry from a reservoir engineering point of view. Some of the main tasks of reservoir engineering are discussed with an emphasis on the importance of appraising reservoirs in the pre-development stage. A brief review of the principal methods and applications of reservoir geochemistry are given, in the context of applications to reservoir engineering problems. The importance of compositional differences in fluid samples from different depths or spatial locations is discussed in connection with the identification of internal flow barriers. The importance of understanding the magnitude and origin of vertical compositional gradients is emphasised because of possible confusion with purely lateral changes. The geochemical origin and rate of dissipation of compositional differences over geological time is discussed.Geochemical techniques suitable for bulk petroleum fluid samples include GC fingerprinting, GCMS, isotopic and PVT measurements. Core sample petroleum extracts may also be studied by standard geochemical methods but with the added complication of possible contamination by drilling mud. Aqueous phase residual salt extracts can be studied by strontium isotope analysis from core samples. Petroleum fluid inclusions allow the possibility of establishing the composition of paleo-accumulations.The problems in predicting flow barriers from geochemical measurements are discussed in terms of “false positives” and “false negatives”. Suggestions are made for areas that need further development in order to encourage the wider acceptance and application of reservoir geochemistry by the reservoir engineering community. The importance of integrating all available data is emphasised.Reservoir geochemistry may be applied to a range of practical engineering problems including production allocation, reservoir compartmentalisation, and the prediction of gravitational gradients. In this review applications where reservoir geochemistry is being used successfully are contrasted with those where applications are less well established.