4 research outputs found
Impact of Diagenetic Alterations on the Petrophysical and Multiphase Flow Properties of Carbonate Rocks Using a Reactive Pore Network Modeling Approach
Sedimentary reservoir rocks generally have complex and heterogeneous pore networks that
are related to the original depositional rock texture and subsequent diagenetic
alterations. Such alterations are in part controlled by the original mineralogy and
sedimentological facies, the compaction history, the involved fluids (and rock/fluid
interactions), the flow history and the related physico-chemical conditions. During the
diagenetic evolution (paragenesis), cycles of alternating dissolution (porosity
enhancement) and precipitation (porosity destruction) caused by changes in chemical and
thermodynamic conditions may lead to heterogeneous rock structure at both local and
reservoir scale.
In the absence of cored plugs to measure the petrophysical properties (i.e. porosity,
permeability and formation factor) and multiphase flow properties (i.e. capillary
pressure, relative permeability and resistivity index), a numerical tool that calculates
these properties from pore structure data by predicting its evolution during the
diagenetic cycle is of great interest for the petroleum industry and reservoir
characterization studies.
A Pore Network Model (PNM) provides opportunities to study transport phenomena in
fundamental ways because detailed information is available at the pore scale. It has been
used over the last decades to understand basic phenomena such as capillarity, multiphase
flow or coupled phenomena. In particular, this modeling approach is appropriate to study
the rock/fluid interactions since the mass exchange at surfaces can be modeled explicitly.
It can provide quantitative information both on the effective transport property
modifications due to the reactions and on the structure evolution resulting from
dissolution/precipitation mechanisms. In the present paper, this approach is used to study
the effect of the diagenetic cycle on the petrophysical properties of carbonate rocks. It
involves three discrete steps. The first step consists of replacing the original complex
pore structure of real porous media by a conceptual network. The second step consists of
resolving the governing equations of the precipitation and dissolution phenomena (i.e.
reactive convection diffusion equation) in the conceptual 3D pore network and deducing the
local reactive fluxes and the motion of the fluid-solid interface. The third step consists
of updating the new pore structure and calculating the new petrophysical properties of the
modified porous media. Those steps are repeated in order to mimic a given diagenetic
scenario. Finally, the multiphase flow properties of the current porous media are
calculated.
The impact of one diagenetic cycle of dissolution and precipitation on the pore networks’
heterogeneity and consequently on the petrophysical properties (i.e. porosity and
permeability) and multiphase flow properties (i.e. relative permeability and capillary
pressure) have been investigated. The permeability and porosity evolution during a given
diagenetic cycle are calculated and analyzed as a function of the relevant dimensionless
numbers (Peclet and Damköhler numbers) that characterize the flow and reaction regime. The
correlation between these numbers and the dissolved/precipitated layer thickness
distribution is investigated.
This work contributes to improve the understanding of the impact of dissolution and
precipitation on permeability and porosity modification. Using the PNM approach,
multiphase flow properties and permeability-porosity relationship have been determined for
different reactive flow regimes. These relationships are relevant input data to improve
the quality of reservoir simulation predictions