The analysis of reservoir heterogeneity from Well Log DATA

All reservoirs are characterized by a sum of matrix and fluids properties. They are evaluated by a complex investigation consisting of core sampling analysis, geological, geophysical and hydrodynamic investigation and production data. These properties can be constant for the whole field when the reservoir is a homogenous one, or these properties can be variable and the reservoir is a heterogeneous one. But, what is the reservoir heterogeneity and how we can find its magnitude? According to Jensen et al (1997), “Heterogeneity is the property of the medium that causes the flood front, the boundary between the displacing and displaced fluids, to distort and spread as the displacement proceeds”. There are more statistics methods (static and dynamic) for determination of reservoir heterogeneity. The static methods are: The Coefficient of Variation, Dykstra-Parsons Coefficient, Lorenz Coefficient and Gelhar-Axness Coefficient. This work is focused on the static methods, more specifically on Lorenz coefficient, while the dynamic methods are not discussed. For calculation the Coefficient Lorenz is necessary to know porosity, permeability and thickness of the reservoir. The number of values has to be enough and have a uniform distribution on the field for a statistical calculus. The following aspects of this application are emphasizing: wide domain of values for permeability data, the number of permeability values is not always enough for statistical analysing methods; the parameters from well logs are more representative and easy to obtain for the whole reservoir. This paper presents a new mathematical model and a novel practical method to evaluate the reservoir heterogeneity with Lorenz Coefficient using properties of rocks determined from well logs. The mathematical model uses field parameters, such as reservoir porosity, porosity of shale, shale volume and thickness to evaluate the reservoir heterogeneity. The technical contribution of this paper consists not only in a novel practical method to evaluate reservoir heterogeneity, but new challenges are expected from a technological point of view. The application data are provided by the wells from the oil structure named Barbuncesti (Beca, C., Prodan, D., 1983). Barbucesti structure is situated in the southern part of the inner (folded) flank of the Eastern Carpathians foredeep, known as the Mio-Pliocene or Diapiric Folds Zone.