Quantitative assessment of areal geological complexity

Background. The article presents a new approach to assessing the geological complexity — quantitative assessment of areal complexity, as well as an alternative methodology for assessing complexity in 1D. Aim. Developing a numerical metric for assessing the geological complexity and creating an algorithm for complexity maps construction. Materials and methods. Generally, complexity describe the reservoir in one number, that often underestimates the real complexity of the deposit. Geological complexity, presented in the article consists of 5 groups: structuraltectonic, facies-lithological, permeability and porosity, secondary alteration and fluid properties, 13 characteristics describe the complexity space of these groups. Each of these characteristics could be presented not only in 1D but also in 2D. The proposed methodology was tested on the company’s assets. Results. The presented examples of complexity maps for several fields show the advantage of 2D complexity estimation in comparison with 1D. The analysis of decomposed complexity estimation (for individual groups) on the company’s assets showed that the key groups of complexity are structural-tectonic, facies-lithological characteristics. Therefore, characteristics that describe these groups should be taken into account during the decision-making process and assets ranking. Conclusion. A methodology of quantitative assessment of areal geological complexity has been developed. This areal assessment allows identify the most “problematic” areas, analyzing existing sources of uncertainty, and also ranking and screening company assets when making strategic decisions.

Classification of residual recoverable and non-recoverable oil reserves by the reservoir complexity index (RCI)

The paper considers a new engineering analytical tool for express oil reserves assessment. Proposed method is based on classifying oil reserves by complexity – reservoir complexity index (RCI). It allows to optimize the development system and form a well interventions program. The method is suggested to use three main parameters for development complexity estimation: reservoir permeability, start watercut (which contains the parameters of the curve of relative permeability, saturation and viscosity) and geological heterogeneity (pattern efficiency). An economic estimation of the well profitability is carried out by calculating PV UDC indicator (unit development cost, CAPEX / total oil production). The advantages of this indicator is that it allows to determine the economic attractiveness and does not require macro parameters and costs for the building well pads Due to the economic assessment and well ranking, it is possible to obtain profitable well pads and select candidates for sidetracking. The novelty of the work lies in the use of an updated methodology for the reservoir complexity index estimation for the remaining recoverable reserves classification. As a result, high-quality tool is created that integrates RCI and economic model. It is aimed for solving reservoir engineering problems and increasing the project cost The proposed method can be applied to other fields with minor modifications.