Modeling of Permeability and Strain Evolution in Chemical Creep Compaction Experiments with Fractured and Unfractured Chalk Cores Conducted at Reservoir Conditions

Abstract

Summary Understanding the effect of typical water-related improved oil recovery techniques is fundamental to the development of chalk reservoirs on the Norwegian Continental Shelf (NCS). We investigate the contribution and interplay of key parameters influencing the reservoir's flow and storativity properties, such as effective stresses, injecting fluid chemistry, and geomechanical deformation. This is done by developing a mathematical model that is applied to systematically interpret experimental data. The gained understanding is useful for improved prediction of permeability development during field life. The model we present is for a fractured chalk core whereby fluids can flow through the matrix and fracture domains in parallel. The core is subject to a constant effective stress above the yield, resulting in time-dependent compaction (creep) of the matrix, while the fracture does not compact. Reactive brine injection causes enhanced compaction but also permeability alteration. This again causes a redistribution of injected flow between the two domains. A previous version of the model parameterizing the relation between chemistry and compaction is here extended to quantify the effect on permeability and see the effect of flow in a fracture-matrix geometry. A vast set of experimental data were used to quantify the relations in the model and demonstrate its usefulness to interpret experimental data. Two outcrop chalk types (Aalborg and Liège) being tested at 130°C and various concentrations of Ca-Mg-Na-Cl brines are considered. However, assumptions were required, especially regarding the fracture behavior because directly representative data were not available. The tests with inert injecting brine were used to quantify the effect of matrix and fracture mechanical compaction on permeability trends. To be able to explain the tests with reactive brine, an important finding is that permeability not only decreased because of enhanced porosity reduction but also because of a quantifiable chemistry-related process (dissolution/precipitation). Sensitivity analyses were performed regarding varying fracture width, injection rate, and chemistry concentration to evaluate the effect on chemical creep compaction and permeability evolution in fractured cores. The model can be used to highlight parameters with great influence on the experimental results. An accurate quantification of such parameters will contribute to refining laboratory experiments and will provide valuable data for upscaling and field application.

An Analytical TOOLBOX for the Characterization of Chalks and Other Fine-Grained Rock Types within Enhanced Oil Recovery Research and Its Application—A Guideline

“…The routine part of the toolbox comprises: All noted methods are positively tested, and detailed methodology recipes exist for chalk [5,6,10,32], ready for application within analytical routines for applied research within the hydrocarbon industry and here focussed on EOR research. The toolbox is designed to enable selecting the quickest and most economic tools to yield necessary datasets for decision making and modelling in this field of HC research and industrial applications (e.g., [5,42]). This concept stresses the need of valuable mineralogical input for simulators to be able to upscale from pore-to core-and field-scale.…”

Reaction Kinetics Determined from Coreflooding and Steady-State Principles for Stevns Klint and Kansas Chalk Injected with MgCl2 Brine at Reservoir Temperature

“…Andersen and Berawala (2019) interpreted a vast set of experimental data to both determine reaction kinetics and the associated impact on creep compaction for Aalborg (Denmark) and Liege (Belgium) chalks. Kallesten et al (2020) extended this methodology to account for flow in compacting fractured chalk with permeability alterations in the matrix and fracture.…”

Permeability Evolution of Shear Failing Chalk Cores under Thermochemical Influence

“…23 In the above review, most of the research has been conducted on whole cores to study the effect of systematically changing effective stress, temperature, and brine composition and see the resulting impact in terms of rock−fluid interactions, compaction, porosity, and permeability. Kallesten et al 29 modeled chemical creep compaction in a fractured core subject to hydrostatic stresses but concluded that more experimental data were needed to characterize the fracture. A limited number of studies have considered fractured cores, deviatoric stress, or doing repeated stress cycles.…”