"Reservoir Description: A Practical Synergistic Engineering and Geological Approach Based on Analysis of Core Data"

Abstract

SPE Member Abstract Description of reservoir rocks in terms of complex variations in hydraulic properties, heterogeneity and geometry requires a synergistic, multidisciplinary engineering and geological approach. This paper presents a practical systematic approach to integration of various core analysis data for reservoir description. Various petrophysical parameters are strongly correlated with pore space attributes using the mean hydraulic radius,. Additionally, empirical equations are presented for transforming lab-derived core properties to appropriate reservoir in-situ stress conditions. Introduction The performance of a hydrocarbon bearing reservoir is largely controlled by certain intrinsic properties of the porous medium. According to Haldorsen, reservoir description can be defined as "Combined efforts aimed at discretizing the reservoir into subunits, such as layers and grid blocks and assigning values of all pertinent physical properties to these blocks." Understanding the complex variations in hydraulic properties (porosity, permeability, capillary pressure, and relative permeability), reservoir heterogeneity and geometry (morphology and continuity) requires a multi-disciplinary synergistic approach that involves the efforts of engineers and geoscientists. Effective description of the reservoir is key to efficient reservoir management. Typically, data from various sources are utilized to describe the reservoir in terms of pore space, attributes, distribution and geological attributes. These sources include cores, logs, seismic tomography, well test and production history data. Harris et al. emphasized the importance of synergy in reservoir management and discussed the interplay of geological and engineering factors on reservoir description. Several other authors (Sneider and King, Hietala et al.; Neasham, Swanson) have discussed the integration of core and log data for formation evaluation. However, none of these authors documented how to appropriately zone the reservoir into hydraulic units or how to average macroscopic parameters for input into numerical simulators. Keelan earlier presented a treatise on the use of core analysis data as aid in reservoir description and reviewed the various analyses (routine, complementary and special) performed on core samples. He discussed the variety of measurement protocols, characterized certain rock properties (porosity, permeability, grain density and capillary pressure) and showed how these properties varied with the geological factors such as the environment of deposition. Core sample analysis provides the fundamental building block for reservoir description. Core specimens are the only representative elements of the reservoir rock that are physically available for examination and modeling of basic flow processes. As such, data from analysis of cores must be properly understood before application in numerical simulators. Whereas core samples provide basic information on the reservoir rock at both microscopic (pore level) and macroscopic (core plug) levels, wireline logs, wireline tests and well tests provide moving averages of reservoir properties on a megascopic level. These megascopic measurements, though representative of a larger volume of scale, must be calibrated with data from the physical model (core specimen) to validate the mathematical models and assumptions on which they are based. Furthermore, it is extremely important to understand the relative volumes of investigation and associated uncertainties of the various reservoir description measurements. This paper presents a practical systematic approach to integration of various core analysis data for reservoir description. Techniques are discussed for zonation of the reservoir into hydraulic units. The roles of geological processes-diagenesis and depositional facies on primary rock properties (texture, fabric, sedimentary structures) and their resultant effects on reservoir rock quality and performance are discussed. Various petrophysical parameters are correlated with pore space attributes (geometry and distribution). Techniques are presented for relating clay morphological properties (types, distribution, location, CEC) to macroscopic rock properties, electrical properties (F, m, n); mean hydraulic radius, capillary pressure, liquid permeability and relative permeability. Empirical equations are derived to relate certain rock properties (porosity, permeability, inertial resistance coefficient/turbulence factor p, and compressional/shear wave velocities) to reservoir stress values. These relationships then permit proper transformation of laboratory derived rock properties to appropriate in-situ stress conditions.

A Universal Formulation for the Prediction of Capillary Pressure

“…This aspect was further studied and reported by Amaefule et al (1988Amaefule et al ( , 1993 and others. While Eq.…”

“…Amaefule et al (1988Amaefule et al ( , 1993 defined new parametric groups: Re w servoir Quality Index (RQI), Porosity Group (PG) and Flow Zone Indicator (FZI), as follows: Amaefule et al (1988Amaefule et al ( , 1993 defined new parametric groups: Re w servoir Quality Index (RQI), Porosity Group (PG) and Flow Zone Indicator (FZI), as follows:…”

“…For further information, the reader is referred to publications by Amaefule et al (1988Amaefule et al ( , 1993. For further information, the reader is referred to publications by Amaefule et al (1988Amaefule et al ( , 1993.…”

Relative Permeability in Dual-Porosity Porous Media

“…8) where the Corey's exponent λ is found to be equal to 0.509 which corresponds to a wide range of pore size as indicated by Amaefule et al 15 and Tiab and Donaldson 17 . 7 and Eq.…”

Well Log Petrophysics of the Cretaceous Pay Zones in Zubair Field, Basrah, South Iraq

“…This requires the conjugated efforts of geoscientists and engineers in a multi-disciplinary synergistic approach to recognize the complex variations in reservoir heterogeneity and its associating hydraulic properties [1]. Such synergistic approach is discussed by Harris et al in [2] and emphasized the importance of geological and engineering approaches for reservoir characterization.…”