Although hydrocarbon transport in organic-rich source rocks has not been understood well, it is believed that spatial connectivity of organic matter within organic-rich source rocks significantly affects production from these reservoirs. However, this parameter has been only qualitatively described based on nanoscale rock images. Previous publications suggest that kerogen can have conductive behavior in reservoir temperature. Consequently, the presence of kerogen in organic-rich source rocks affects their electrical resistivity. This paper quantifies the impact of spatial connectivity/distribution of kerogen network on electrical resistivity of organic-rich source rocks.
We use pore-scale numerical simulations to estimate electrical resistivity in the presence of kerogen in organic-rich source rocks. We also introduce a directional kerogen network connectivity factor along different directions based on Euler-Poincare Characteristic (EPC). We then calculate electrical resistivity of three-dimensional (3D) pore-scale synthetic examples of organic-rich source rocks with different levels of kerogen network connectivity.
The results obtained from numerical simulations in synthetic organic-rich source rocks confirmed that
the presence of conductive kerogen can significantly impact electrical resistivity of the rock and the corresponding assessment of fluid saturations based on electrical resistivity measurements and
spatial distribution and connectivity of kerogen network have measureable impact on electrical resistivity of the rock.
Neglecting the presence of conductive kerogen can lead to 25% overestimate in water saturation. We also observed up to 37% variation in electrical resistivity caused by variation in directional connectivity of kerogen network, ranging from dispersed to layered kerogen distribution.
Electrical resistivity logs are among the most important conventional well logs for petrophysical/fluid evaluation of conventional reservoirs. Resistivity-porosity-saturation models (e.g., Archie'S, Dual-Water and Waxman-Smits equations) have been conventionally used to correlate borehole electrical resistivity measurements to pore-scale petrophysical properties in conventional reservoirs. All the conventional resistivity-porosity-saturation models assume that saline water is the only conductive component of the rock-fluid system. In the case of organic-rich source rocks, however, highly mature conductive kerogen and typical abundance of conductive pyrite can affect measurement of borehole electrical resistivity.