Abstract

The Digital Rock Physics (DRP) technology is based on a rigorous numerical simulation of physical experiments in a realistic pore space, at the pore-scale level. The output is usually a macroscopic property conventionally measured in the lab. For example, single-phase viscous fluid flow simulation through a digitized pore space provides absolute permeability. A simulation of electrical current provides conductivity, and a simulation of the stress field provides the elastic moduli and strength. DRP complements lab measurements and, at the same time, enormously enhances the geoscientist's capabilities because digital experiments can be conducted in real time and on small fragments of rock, such as drill cuttings.

In this paper, results of a feasibility study on DRP technology is reported using for the first time the drill cutting samples in obtaining petrophysical properties including permeability and porosity of formations. This real-time technology may become very beneficial to the industry once it is established that the results are reliable.

The 3D digital pore space needed for numerical simulation has been recreated from 2D images by means of statistical simulation. An example is also presented where the 3D digital pore space was obtained by direct CT scanning of drill cutting. The resulting macroscopic rock properties have been compared to independently obtained core data from laboratory measurements and log data from the same interval where cuttings are obtained.

Introduction: Background and Techniques

Porosity and permeability are key petrophysical properties in petroleum industry and environmental applications. Currently, detailed special distribution of permeability cannot be directly obtained in-situ. Decades of analysis of numerous laboratory data points failed to produce universal and robust transforms between permeability and other rock properties such as porosity, lithology, and texture due to extreme variability of the pore space topology in rocks. This variability is caused by two principal factors:

  1. variations in deposition and

  2. variations in diagenesis.

The most reliable, and, essentially, the only way of measuring permeability is in the laboratory on physical core plugs.

In this study, we adopted the concept of virtual (or numerical) experimentation. Specifically, we simulated viscous fluid flow through a realistic pore space numerically represented by zeros (pores) and ones (mineral phase). One advantage of virtual experimentation over physical experimentation is that the former is non-destructive, i.e., a 3D pore space structure that is reconstructed from very small rock drill cuttings can be reused many times in a number of numerical experiments. Also, a 3D pore space can be reconstructed from sidewall plugs that often cannot be used for physical permeability measurements because of the damage during plug recovery. Finally, once a 3D numerical representation of a pore space is constructed, it can be numerically altered to reflect variations in diagenesis and sorting. The virtual experimentalist can tremendously expand the database without using additional cores/cuttings when the DRP technique is implemented.

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