Evaluation of reservoir heterogeneity using well log curves

Abstract

Each productive horizon, the subject of geo-logical and geophysical research, formed under unique conditions. Different types of rock facies can typically be grouped based on sediment accumulation environments (continental, deltaic or coastal-marine), the diagnostic features of these types and paleohydrodynamic sedimentation conditions. These groups share certain common geological and geophysical characteristics. However, these characteristics are generalised and de-scribe the reservoir as a whole without focusing on the details of its geological structure. Specifically, heterogeneities such as the presence of highly permeable layers within the formation, variability in filtration properties along the productive interval penetrated by the well, uneven distribution of fracturing or caverns and the nature of the cementing material are often overlooked. During the development of oil and gas fields, the geological features of reservoirs have a decisive impact on the efficiency of hydrocarbon recovery, often leading to premature water breakthrough or the formation of water coning. In the modern era, oil and gas field development projects are implemented using digital geological models as standard. These models are highly accurate due to the high level of detail of the reservoirs. This is achieved through a comprehensive set of geological, geophysical and production data, including core laboratory studies, well logging and trial and pilot pro-duction results, as well as modern mathematical and statistical processing methods. However, due to objective reasons, such datasets often lack either sufficient core material or data from the initial stages of reservoir development. Consequently, well logging curves remain the most readily available source of information. In our opinion, these curves offer extensive possibilities for assessing reservoir heterogeneities, many of which re-main unexplored by researchers. In this study, the authors propose a modified approach to using the Dakhnov–Archie formula, expressing it through the structur-al coefficient and utilising well logging data obtained through point-by-point interpretation for calculations. These calculated structural coefficients enable detailed assessment of the heterogeneity of the productive interval penetrated by the well, as well as prediction of fluid flow dynamics in different parts of the reservoir.