Porosity-permeability Evolution Research Articles

The role of salt dissolution on the evolution of petrophysical properties in saline-lacustrine carbonate reservoirs: Pore structure, porosity–permeability, and mechanics

The invasion of low-salinity fluids into saline-lacustrine reservoirs may induce salt dissolution, resulting in significant changes in petrophysical properties. Accurate characterization of these changes due to salt dissolution is critical for efficient drilling and development. Here, low-salinity core flooding experiments and several core analysis technologies were employed to investigate the changes in pore structure, porosity–permeability evolution, and mechanical properties. Ion compositions in outlet fluids analyzed in real-time to determine the dissolved salt mineral compositions, mainly include halite (1.66 %), anhydrite (7.32 %), and glauberite (0.98 %). Salt dissolution produces many dissolution pores, especially with sizes ranging from 0.01 to 10 μm, broadens the seepage channels, and enhances the connectivity between pores, which significantly improves rock porosity close to 1.80 times the initial one and permeability to 70 times initial one. During the salt dissolution process, the stability of clay minerals is weakened to induce dispersion, migration, and swelling behavior, leading to the reduction of porosity and permeability. A semi-empirical power law relating expressing porosity and permeability for saline-lacustrine reservoirs is proposed, allowing for salt dissolution and clay swelling during the invasion process of low-salinity fluids. Although salt dissolution could slightly relieve stress sensitivity damage by 56.54 %, it significantly weakens rock strength by reduction of elastic modulus (43.51 %) and compressive strength (61.54 %). The positive and negative effects of salt dissolution on petrophysical properties are critical to guide the development of formation damage control measures for saline-lacustrine reservoirs.

Pore-scale investigation on mineral dissolution and evolution in hydrological properties of complex porous media with binary minerals

A pore-scale numerical model for reactive transport process based on lattice Boltzmann method is adopted to simulate the mineral dissolution in complex porous media with binary minerals. The effect of binary mineral, solute concentration and dissolution rate on hydrological properties evolution of complex porous media is investigated. Simulation results show that binary minerals could inhibit the mineral dissolution and further alter the temporal evolution trend of related hydrological properties compared to monomineralic porous media. Changes in pore structure of complex porous media could be divided into three stages: slow increase, significant increase and slightly-stable increase stage in succession. A simple model is barely suitable for characterizing the porosity-permeability evolution of the complex porous media. Temporal evolution in reactive specific surface during mineral dissolution could be characterized by the fractal model. Although solute concentration could change the mineral dissolution process, it has no effect on the evolution relationship of hydrological properties between permeability, reactive specific surface and porosity. Mineral dissolution rate would alter the above-mentioned relationships by changing the reactive transport regime.

Numerical study of the porosity-permeability evolution due to chmically-active fluid injection

The paper presents a numerical algorithm for simulation of the reactive transport at the pore scale. The algorithm allows simulating pore space evolution, porosity, absolute permeability, and form factor changes due to core matrix dissolution or precipitation. We also, introduce the topological measure; the persistence diagrams of independent cycles in pore space to classify different dissolution scenarios. Using derived classification, we constructed the statistically reliable porosity-permeability relations for different dissolution scenarios.

Pore-merging methodology for reactive transport and mineral dissolution in pore-network models

This study proposes a pore-network modeling algorithm to simulate single-phase reactive transport and mineral dissolution in porous media. A novel pore-merging approach is introduced to guarantee the conservation of the most critical variables during the merging process by using correction factors and effective properties for throat conductances and surface areas. Our approach solves a coupled transport and reaction pore-network model that implements a kinetic model with a single heterogeneous chemical reaction describing the dissolution of calcite by acidic solutions. The network geometry is updated based on the dissolution process occurring at the mineral surface and the network topology is updated based on the pore-merging processes occurring throughout the network. The main results include the exploration of different dissolution regimes through porosity-permeability evolution curves, acid concentration profiles, and the use of statistical criteria. Importantly, this methodology simulates permeability increases larger than 100-fold during the formation of preferential pathways (i.e., wormholes).

The coal inter-particle stress and porosity-permeability evolution characteristics of the confined coal by the applied loading relief effects

The coal inter-particle stress and porosity-permeability evolution characteristics of the confined coal by the applied loading relief effects

Reservoir Scale Porosity-Permeability Evolution in Sandstone Due to CO2 Geological Storage

CO2 injection into geological reservoirs is considered as a promising technology to improve oil recovery from oil reservoirs and to reduce greenhouse gas emissions. However, due to the density difference between the injected CO2 and formation brine, the injected CO2 tends to move vertically towards the surface. The risk of this vertical CO2 movement can be prevented by four different trapping mechanisms (i.e. structural, residual, dissolution, and mineral trapping). From the dissolution of CO2 in the aquifer brine, carbonic acid will be formed. Then, this carbonic acid will be reacted with rock minerals and resulted in mineral dissolution and precipitation. However, the effect of these mineral interactions on the porosity-permeability evolution during the CO2 storage process in the sandstone reservoir has not been addressed effectively. Thus, here, we developed a 3D reservoir simulation model to investigate the effect of mineral interactions on the reservoir porosity and permeability during CO2 injection and storage processes in a sandstone reservoir. The multicomponent, chemically reactive, non-isothermal and multiphase flow numerical simulation program TOUGHREACT has been used. The model length was 1000 m, model width was 1000 m and the model thickness was 1000 m (ranging from top depth of 1000 m and bottom depth of 2000 m) with a regularly spaced grid of 15 × 15 × 48 grid (10800 gridblocks). The developed reservoir simulation model consists of two main regions which are reservoir rock region (sandstone) and cap rock region (shale). The simulated sandstone formation consists of quartz, kaolinite, chlorite, and illite. Our results show that CO2 injection leads to significant mineral reactionس (dissolution and precipitation) in the sandstone reservoir. Furthermore, the results indicate that these mineral reactions lead to increase in the sandstone porosity and permeability during the storage period. Thus, we conclude that the mineral reactions (dissolution and precipitation) due to CO2 injection in the sandstone reservoir affect the sandstone porosity and permeability, and hence, affect the CO2 geological storage capacity.

Changes in pore structures and porosity-permeability evolution of saline-lacustrine carbonate reservoir triggered by fresh water-rock reaction

Salt dissolution occurs frequently during the drilling, water-flooding development and other operations of saline-lacustrine carbonate reservoirs, greatly changing the petrophysical properties of rocks. To understand the salt dissolution behavior and its effect on the rock structures, core-flooding and crushed sample soaking experiments are conducted on saline-lacustrine carbonate samples. Results indicate that ion concentration from core flooding experiments increases first and then decreases fast with time proceeding, while it has a positive e-based logarithmic relation with soaking time from sample soaking experiments. According to ion analysis, the main dissolved salt minerals include halite, anhydrite and glauberite. With the size increase of crushed samples, the dissolved mass is decreased, having a positive logarithmic relation with sample specific surface, and sample specific surface is logarithmically increased with soaking time. Rock capillary pressure curves get lower, and pore throat size distributions become wider than those before dissolution of salt minerals. Salt dissolution mainly affects the pore microstructure with size ranging from 0.01 to 10 μm, while having little effect on nanopores <0.01 μm. Salt dissolution could make the clay swelling and fine migration, inhibiting the increment in porosity and permeability. In addition, rock permeability has a power relation with porosity during the dissolution, and a permeability-growth-controlling threshold porosity is observed, which indicates the transformation point of dissolution area from pore bodies to throats. Furthermore, a mathematical model for characterization of rock porosity and permeability evolution relationship is derived, which allows for rock microstructure, salt composition and dissolution, and clay composition and swelling behavior.

CO2 storage in the Paluxy formation at the Kemper County CO2 storage complex: Pore network properties and simulated reactive permeability evolution

The Paluxy formation is being considered as a prospective CO2 reservoir at the Kemper County CO2 Storage Complex. Here, the pore and pore-throat size distributions and connectivity of the Paluxy formation is evaluated through analysis of 3D X-ray Computed Tomography images. In spite of resolution limitations that constrain the pore-throat sizes detectable by imaging, the permeability contributing pore-throats are successfully characterized through 3D imaging analysis. Image-obtained pore and pore-throat size distributions and pore connectivity are then utilized to construct pore network models and simulate permeability. After CO2 is injected, it will dissolve into formation brine and create conditions favorable for dissolution of primary minerals and precipitation of secondary minerals. These reactions will alter the porosity and permeability of the system to varying degrees depending on the spatial location of reactions. Here, the possible porosity-permeability evolution is simulated using pore network models considering mineral reactions occurring uniformly and non-uniformly throughout the network. For a given change in porosity, there is a large range of possible permeability outcomes. Depending on the extent and spatial location of mineral reactions, permeability may decrease by more than one order of magnitude as minerals precipitate. During dissolution, simulated permeability increases as much as 500%.

Universal scaling of fluid permeability during volcanic welding and sediment diagenesis

In sedimentary basins and volcanic edifices, granular materials undergo densification that results in a decrease of porosity and permeability. Understanding the link between porosity and permeability is central to predicting fluid migration in the sedimentary crust and during volcanic outgassing. Sedimentary diagenesis and volcanic welding both involve the transition of an initially granular material to a non-granular (porous to dense) rock. Scaling laws for the prediction of fluid permeability during such granular densification remain contested. Here, based on collated literature data for a range of sedimentary and volcanic rocks for which the initial material state was granular, we test theoretical scaling laws. We provide a statistical tool for predicting the evolution of the internal surface area of a system of particles during isotropic diagenesis and welding, which in turn facilitates the universal scaling of the fluid permeability of these rocks. We find agreement across a large range of measured natural permeabilities. We propose that this result will prove useful for geologists involved in modeling porosity-permeability evolution in similar settings.

Effects of pore-scale precipitation on permeability and flow

The effects of calcite precipitation on porous media permeability and flow were evaluated with a combined experimental and modeling approach. X-ray microtomography images of two columns packed with glass beads and calcite (spar crystals) or aragonite (Bahamas ooids) injected with a supersaturated solution (log Ω = 1.42) were processed in order to calculate rates of calcite precipitation with a spatial resolution of 4.46 µm. Identification and localization of the newly precipitated crystals on the 3D images was performed and results used to calculate the crystal growth rates and velocities. The effects of carbonate precipitation were also evaluated in terms of the integrated precipitation rate over the length of the column, crystal shape, surface area and pore roughness changes. While growth was epitaxial on calcite spar, calcite rhombohedra formed on glass beads and clusters of polyhedrons formed on aragonite ooids. Near the column inlet, calcite precipitation occurred preferentially on carbonate grains compared to glass beads, with almost 100% of calcite spar surface area covered by new crystals versus 92% in the case of aragonite and 11% in the case of glass beads. Although the experimental chemistry and flow boundary conditions in the two columns were similar, their porosity-permeability evolution was different because the nucleation and subsequent crystal growth on the two substrates (i.e., calcite spar and aragonite ooids) was very different. The impact of mineral precipitation on pore-scale flow and permeability was evaluated using a pore-scale Stokes solver that accounted for the changes in pore geometry. For similar magnitude reductions in porosity, the decrease in permeability was highest within the sample that experienced the greatest increase in pore roughness. Various porous media models were generated to show the impact of different crystal growth patterns and pore roughness changes on flow and permeability-porosity relationship. Under constant flow rate boundary conditions, precipitation resulted in an increase in both the average and maximum velocities. Increases in pore roughness led to a more heterogeneous flow field, principally through the effects on the fastest and slowest velocities within the domain.

Diagenesis and porosity-permeability evolution of low permeability reservoirs: A case study of Jurassic Sangonghe Formation in Block 1, central Junggar Basin, NW China

Abstract Based on core observation, thin section examination, cathode luminescence analysis, scanning electron microscopy, fluid inclusions, carbon and oxygen isotope, mercury penetration, porosity-permeability test and other analytical methods, combined with the histories of burial evolution, organic matter thermal evolution and hydrocarbon charge, the diagenesis and porosity-permeability evolution are studied of low-permeability reservoirs of Jurassic Sangonghe Formation in Block 1 of central Junggar Basin. The matching relation between reservoir porosity-permeability evolution and hydrocarbon accumulation history is analyzed. The diagenetic environment evolution of the reservoir in the study area is early alkaline, interim acid and late alkaline, forming the diagenetic sequence of chlorite membrane precipitation, early calcite cementation, feldspar dissolution accompanied by quartz overgrowth and authigenic kaolinite precipitation, anhydrite cementation, late period ferrocalcite and ankerite cementation, a small amount of pyrite cementation. Generally, compaction occurs throughout the whole burial process. According to the matching relation between reservoir porosity-permeability evolution and hydrocarbon accumulation history, the Jurassic Sangonghe Formation has three genetic types of low permeability reservoirs: densification after hydrocarbon accumulation, with the best exploration potential; densification during the hydrocarbon accumulation, with medium exploration potential; densification before the hydrocarbon accumulation, with the poorest exploration potential.

Pore network modelling to determine the transport properties in presence of a reactive fluid: From pore to reservoir scale

The study of CO2 sequestration evolution during a reservoir storage project depends on the accurate determination of three macroscopic parameters governing the solute displacement, namely the solute velocity, the dispersion and the mean reaction rate. These parameters are computed for a surface reaction by a pore network modelling technique. A pore network, extracted from micro tomography images is used in order to calculate the macroscopic transport parameters and porosity–permeability evolution during reactive transport as functions of the dimensionless numbers characterizing the reaction and flow rate regimes. Finally, the influence of these macroscopic parameters on CO2 plume evolution is studied for a synthetic reservoir field.

Quantification and Prediction of the 3D Pore Network Evolution in Carbonate Reservoir Rocks

This study presents an integrated approach that allows the reconstruction and prediction of 3D pore structure modifications and porosity/permeability development throughout carbonate diagenesis. Reactive Pore Network Models (PNM-R) can predict changes in the transport properties of porous media, resulting from dissolution/cementation phenomena. The validity and predictability of these models however depend on the representativeness of the equivalent pore networks used and on the equations and parameters used to model the diagenetic events. The developed approach is applied to a real case of a dolostone rock of the Middle East Arab Formation. Standard 2D microscopy shows that the main process affecting the reservoir quality is dolomitisation, followed by porosity enhancement due to dolomite dissolution and secondary porosity destruction by cementation of late diagenetic anhydrite. X-ray μ -CT allows quantifying the 3D volume and distribution of the different sample constituents. Results are compared with lab measurements. Equivalent pore networks before dolomite dissolution and prior to late anhydrite precipitation are reconstructed and used to simulate the porosity, permeability characteristics at these diagenetic steps. Using these 3D pore structures, PNM-R can trace plausible porosity-permeability evolution paths between these steps. The flow conditions and reaction rates obtained by geochemical reaction path modeling can be used as reference to define PNM-R model parameters. The approach can be used in dynamic rock typing and the upscaling of petrophysical properties, necessary for reservoir modeling.

Porosity–permeability relationships in Miocene carbonate platforms and slopes seaward of the Great Barrier Reef, Australia (ODP Leg 194, Marion Plateau)

AbstractThis paper reports a series of 700 porosity–permeability analyses and supporting petrographic and sedimentologic descriptions from Early to Late Miocene carbonate strata cored on the Marion Plateau, offshore from north‐eastern Australia, during Ocean Drilling Program (ODP) Leg 194. The samples analysed are not only mainly coarse bioclastic limestones and dolomitized equivalents from platform‐top facies, but also include 79 plugs from deeper‐water slope to hemipelagic drift facies. Outstanding characteristics of this data set are the wide ranges of porosity and permeability in both limestones and dolostones, the large degree of short‐range heterogeneity typical of these strata, and the better porosity–permeability correlation of dolostones than limestones. The platforms have experienced widely varying calcite cementation, dolomitization and dissolution but show little clear evidence of meteoric diagenesis, suggesting that subaerial exposure may have played little role in porosity–permeability evolution. Permeability‐for‐given‐porosity is controlled by grain size and calcite cement content in grainstones and by occurrence of larger shelter pores and vugs in mud‐rich samples. Dolomitization tends to reduce the variation of permeability‐for‐given‐porosity by recrystallizing mud matrix to form intercrystalline macroporosity that connects vugs and moulds to become integrated with the effective pore system. As a result, there are no differences in permeability–porosity trends for different dolostone textures, whether dominated by intercrystalline, vuggy, or preserved intergranular pore types. Two platform‐top sites separated by only 5 km display a major lateral variation in dolostone porosity–permeability characteristics within the youngest dolostone units. This difference is interpreted as reflecting a relatively ‘windward’ (current‐facing) setting of the site with the overall higher permeability‐for‐given‐porosity (Site 1199) that led to less muddy depositional facies, greater cementation, and lesser grain dissolution. Pore‐geometry parameters measured by petrographic image analysis confirm that the ‘windward’ dolostones have pores that are both larger and less intricate than dolostones comprising the more current‐protected location.