Jinfang Gao

Lattice Boltzmann modeling and evaluation of fluid flow in heterogeneous porous media involving multiple matrix constituents

Geomaterials are typical heterogeneous porous media involving multiple types of matrix constituents which dominate the subsurface flow behavior. An improved lattice Boltzmann method (LBM) approach is developed for analyzing the detailed flow characteristics through multiple matrix constituents, investigating sample size effects on the permeability variation, and evaluating characteristic information at the representative elementary volume (REV) scale for the macroscale reference. Applications are conducted in both 2D and 3D to numerically investigate the impact of geometric topology and matrix property on the detailed velocity field, and effects of sample sizes on the permeability for evaluating effective REV scale fluid flow parameters. The simulation results demonstrate that the improved LBM approach is able to quantitatively describe and simulate complex fluid flow through multiple-matrix constructed heterogeneous porous media, which provides more realistic simulation results for up-scaled research and engineering. Quantitative modeling of detailed heterogeneous porous media flow involving multiple permeable minerals.Investigating sample size effects on the permeability variation and the flow flux.Evaluating characteristic information at the representative element volume (REV) scale for the macroscale reference.Providing meaningful REV scale parameters for relative up-scaling research.2D/3D applications in porous flows involving quartz, clay, feldspar and cavities.

Recent development in numerical simulation of enhanced geothermal reservoirs

This paper briefly introduces the current state in computer modelling of geothermal reservoir system and then focuses on our research efforts in high performance simulation of enhanced geothermal reservoir system. A novel supercomputer simulation tool has been developing towards simulating the highly non-linear coupled geomechanical-fluid flow-thermal systems involving heterogeneously fractured geomaterials at different spatial and temporal scales. It is applied here to simulate and visualise the enhanced geothermal system (EGS), such as (1) visualisation of the microseismic events to monitor and determine where/how the underground rupture proceeds during a hydraulic stimulation, to generate the mesh using the recorded data for determining the domain of the ruptured zone and to evaluate the material parameters (i.e., the permeability) for the further numerical analysis and evaluation of the enhanced geothermal reservoir; (2) converting the available fractured rock image/fracture data as well as the reservoir geological geometry to suitable meshes/grids and further simulating the fluid flow in the complicated fractures involving the detailed description of fracture dimension and geometry by the lattice Boltzmann method and/or finite element method; (3) interacting fault system simulation to determine the relevant complicated rupture process for evaluating the geological setting and the in-situ reservoir properties; (4) coupled thermo-fluid flow analysis of a geothermal reservoir system for an optimised geothermal reservoir design and management. A few of application examples are presented to show its usefulness in simulating the enhanced geothermal reservoir system.

Parallel Lattice Boltzmann Computing and Applications in Core Sample Feature Evaluation

Micro-CT scans with QEMSCAN mapping provide visualization of core samples to quantify heterogeneous physical properties important for subsurface flow including, as examples, pore size distribution and connectivity, mineral compositions, porosity and permeability, amongst many others. 3D high-resolution micro-CT scans can deliver a very high level of microstructures detail, which also implies enormous numerical data sets and associated computational processing load. It is, therefore, important to understand (1) the voxel resolution of micro-CT scans required to retain physical structure fidelity (e.g., mineral compositions, pore size and throats, and porosity and tortuosity), (2) the sensitivity of individual mineral property and voxel resolution on the directional permeability, and (3) the smallest sample size that provides reliable and representative transport calculations (e.g., directional permeability and connectivity). The lattice Boltzmann method is capable of simulating flow in both open pore spaces and porous media and is used here to allow for flow in multiple matrices (quartz aggregate and low-permeable clay matrix). As an application example, a permeability study of the Precipice Sandstone from the Chinchilla 4 well in the Surat Basin has been conducted. Regarding the Chinchilla sample, we established that (1) the composition ratio is relatively sensitive to voxel resolution: higher resolution imaging is required to retain narrow pore throats and excessively coarsened voxel resolutions result in severe loss of internal microstructures information; (2) both voxel resolutions and individual mineral properties affect flow dynamics, and the clay permeability slightly affects the whole permeability at

LBM simulation of fluid flow in fractured porous media with permeable matrix

\sim

High Performance Simulation of Complicated Fluid Flow in 3D Fractured Porous Media with Permeable Material Matrix Using LBM

∼nD scale; (3) it is not feasible to define the accurate ratio of lattice nodes versus pore apertures for meeting the grid independence due to the complex sample tortuosity; and (4) the directional permeability approaches a constant value as the sample size increases to its representative elementary volume scale size (10 mm in this case). Significantly smaller sample sizes cannot retain the representative physical structure fidelity even using higher resolution imaging.

Numerical investigations on the impact of fracture characteristics on elastic anisotropy in coal seam gas reservoirs

Abstract Injection of CO 2 subsurface may lead to chemical reactivity of rock where CO 2 is dissolved in groundwater. This process can modify pore networks to increase or decrease porosity through mineral dissolution and precipitation. A lattice Boltzmann (LB) based computational model study on the pore scale reactive transport in three dimensional heterogeneous porous media (sandstone consisting of both reactive and non-reactive minerals) is described. This study examines how fluid transport in porous materials subject to reactive conditions is affected by unsteady state local reactions and unstable dissolution fronts. The reaction of a calcite cemented core sub-plug from the Hutton Sandstone of the Surat Basin, Australia, is used as a study case. In particular, the work studies the interaction of acidic fluid (an aqueous solution with an elevated concentration of carbonic acid) with reactive (e.g. calcite) and assumed non-reactive (e.g. quartz) mineral surfaces, mineral dissolution and mass transfer, and resultant porosity change. The proposed model is implemented in our custom LBM code and suitable for studies of multiple mineral reactions with disparate reaction rates. A model for carbonic acid reaction with calcite cemented sandstone in the CO 2 -water-rock system is verified through laboratory experimental data including micro-CT characterization before and after core reaction at reservoir conditions. The experimentally validated model shows: (1) the dissolution of calcite cement forms conductive channels at the pore scale, and enables the generation of pore throats and connectivity; (2) the model is able to simulate the reaction process until the reaction equilibrium status is achieved (around 1440 days); (3) calcite constituting a volume of around 9.6% of the whole core volume is dissolved and porosity is consequently increased from 1.1% to 10.7% on reaching equilibrium; (4) more than a third of the calcite (constituting 7.4% of the total core volume) is unaffected, which suggests that this calcite is not connected with open pores (at the resolution of the model) that the acidic fluid can access. The model enables exploration of the porosity change in systems as they react, which has applications for analysis of the induced permeability change at the macroscale.

A coupled lattice Boltzmann model for simulating reactive transport in CO2 injection

To analyze and depict complicated fluid behaviors in fractured porous media with variably permeable matrix, an integrated discrete computational algorithm is proposed based on lattice Boltzmann method (LBM). This paper combines with the external force model and statistical material physics to effectively describe the feature changes while the fluid passes through the fractures within the permeable matrix. As an application example, a two dimensional rock sample is reconstructed using the digital image and characterized with different feature values at each LBM grid to distinguish pores, impermeable and permeable matrix by stating its local physical property. Compared with the conventional LBM, the results demonstrate the advantages of proposed algorithm in modeling fluid flow phenomenon in fractured porous media with variably permeable matrix.

Towards an Integrated Simulator for Enhanced Geothermal Reservoirs

Micro-CT scans provide visualization of core samples that can be used to quantify physical properties important for subsurface flow including, as examples, porosity and pore size distribution, pore connectivity and permeability, amongst many others. 3D scans can deliver a very high level of detail, but at a cost of many hours of scan time. This also implies enormous numerical datasets and associated computational processing load. It is therefore important to understand (1) the voxel resolution that is required to retain physical structure fidelity (e.g., pore size and tortuosity) and (2) the smallest sample size that provides reliable and representative transport calculations (e.g., directional permeability and connectivity). As an application example, we analyze a 3D sandstone sample from the Chinchilla area of the Surat Basin comprising a cuboid of 6.6 mm × 6.6 mm × 12.276 mm. The CT image at 6.6 urn voxel resolution generates 1.86 billion grid elements. The work then examines the effect on physical properties and flow simulation of coarsening the voxel resolution, and reducing the physical size of the sample. For each of the different cases relating to voxel size, the major physical properties are evaluated. For different sample sizes at constant (small) voxel size, the fluid flow is modeled using a lattice Boltzmann method (LBM) on multicore supercomputers. The LBM is efficient and convenient for application in parallel computing, which is required to meet the computational resources needs of 3D simulations with large datasets. Comparison of the results obtained at different resolution scales reveals the minimum representative elementary volume (REV) for voxels to characterize the physical features of porous media, and for sample sizes that effectively eliminate boundary effects, capturing and describing the transport phenomena that underpin reservoir analysis.