Evaluation of reservoir heterogeneity using well log curves

Abstract

Each individual productive horizon, which is the subject of geological and geophysical research, has formed under unique conditions. Typically, different types of rock facies can be grouped based on sediment accumulation environments (continental, deltaic, or coastal-marine), diagnostic features of these types, paleohydrodynamic sedimentation conditions, and other factors. Such groups share certain common geological and geophysical characteristics. However, these remain generalized characteristics that describe the reservoir as a whole, without focusing on the details of its geological structure. Specifically, such heterogeneities as the presence of highly permeable layers within the formation, variability of filtration properties along the productive interval penetrated by the well, uneven distribution of fracturing or caverns, and the nature of the cementing material, among others, are often overlooked. During the development of oil and gas fields, such geological features of reservoirs have a decisive impact on hydrocarbon recovery efficiency, often leading to premature water breakthrough or the formation of water coning. At the modern stage, oil and gas field development projects are implemented with the mandatory use of digital geological models. The high accuracy of these models is ensured by a high degree of reservoir detail. This is achieved through a comprehensive set of geological, geophysical, and production data, including core laboratory studies, well logging, results from trial and pilot production, and modern mathematical and statistical processing methods. However, due to objective reasons, such datasets often lack either a sufficient amount of core material or data from the initial stages of reservoir development. As a result, 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 remain unexplored by researchers. In this study, the authors propose a modified approach to using the Archie-Dakhnov formula by expressing it through the structural coefficient and utilizing well logging data obtained through point-by-point interpretation for calculations. The calculated point-wise structural coefficients enable a detailed assessment of the heterogeneity of the productive interval penetrated by the well and allow for predicting fluid flow dynamics in different parts of the reservoir.