Abstract
Some of the world best hydrocarbon reservoirs (carbonates and siliciclastics) are also believed to be valuable for subsurface storage of CO2 and other fluids. Yet, these reservoirs are heterogeneous in terms of their mineralogy and flow properties, at varying spatial-temporal scales. Therefore, predicting the porosity and permeability (flow properties) evolution of carbonates and sandstones remains a tedious task. Diagenesis refers to the alteration of sedimentary rocks through geologic time, mainly due to rock-fluid interactions. It affects primarily the flow properties (porosity and permeability) of already heterogeneous reservoir rocks. In this project a new approach is proposed to calculate/quantify the influence of diagenetic phases (e.g. dissolution, cement plugging) on flow properties of typical sandstone reservoir rocks (Early Jurassic Luxembourg Formation). A series of laboratory experiments are performed in which diagenetic phases (e.g. pore blocking calcite cement in sandstone) are selectively leached from pre-studied samples, with the quantification of the petrophysical characteristics with and without cement to especially infer permeability evolution. Poorly and heavily calcite-cemented sandstone samples, as well as some intermediate cemented samples were used. The results show a distinctive dissolution pattern for different cementation grades and varying Representative Elementary Volumes (REVs). These conclusions have important consequences for upscaling diagenesis effects on reservoirs, and the interpretation of geochemical modelling results of diagenetic processes. The same approach can be applied on other type of cements and host-rocks, and could be improved by integrating other petrophysical analyses (e.g. petroacoustic, NMR).
Highlights
Heterogeneity is an inherent characteristic of reservoir rocks, which is determined by their geological evolution, e.g. sedimentary origin, diagenetic processes and burial history (Nader, 2016, and references therein)
Computer Tomography (CT) coupled with a flow apparatus and numerical solutions proved to be a successful approach for achieving this objective
The visualization of the connectivity of the pore network and the detection of additional phases result in a detailed characterization of the geological samples
Summary
Heterogeneity is an inherent characteristic of reservoir rocks, which is determined by their geological evolution, e.g. sedimentary origin, diagenetic processes and burial history (Nader, 2016, and references therein). The accurate characterization of reservoir rocks requires a quantitative geometric description of the complex microstructure of the rocks and the use of exact or approximate solutions of the equations of motion that govern For this contribution, carbonate cementation is taken as a case study of diagenetic influence on reservoir rocks. A profound knowledge on the origin, distribution and geometry of carbonate cementation is of prime importance in reservoir characterization, since extensively cemented zones may act as a barrier for fluid flow. They can even lead to reservoir compartmentalisation (Gibbons et al, 1993; Prosser et al, 1993). As stated above this will have great influence on the petrophysical characterization of the potential reservoir
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