Piroska Lorinczi

Direct and Inverse Methods for Determining Gas Flow Properties of Shale

Gas flow in shale is a poorly understood and potentially complex phenomenon. It is currently being investigated using a variety of techniques including the analysis of transient experiments conducted on full core and crushed shale using a range of gases. A range of gas flow mechanisms may operate including continuum flow, slippage, transitional flow and Knudsen diffusion. These processes as well as gas sorption need to be taken into account when interpreting experimental data and extrapolating the results to the subsurface. A finite volume method is developed in this paper to mathematically model gas flow in shale. The finite volume method combines the efficiency/simplicity of finite difference methods with the geometric flexibility of the finite element approach. The model is applicable to non-linear diffusion problems, in which the permeability and fluid density both depend on the scalar variable, pressure. The governing equation incorporates the Knudsen number, allowing different flow mechanisms to be addressed, as well as the gas adsorption isotherm. The method is validated for unsteady-state problems for which analytical or numerical solutions are available. The method is then applied for solving a pressure-pulse decay test and a comparison with an alternative finite-difference numerical solution is made. An inverse numerical formulation is generated, using a minimisation iterative algorithm, to estimate different number of unknown parameters. Both numerically simulated noisy and experimental data are input into the formulation of the inverse problem. Error analysis is undertaken to investigate the accuracy of results. A good agreement between inverted and exact parameter values is obtained. Results for inversions done for practical laboratory pressure-pulse decay tests of samples with very low permeability are also presented.

Stratigraphic correlation and paleoenvironmental analysis of the hydrocarbon-bearing Early Miocene Euphrates and Jeribe formations in the Zagros folded-thrust belt

The Lower Miocene Euphrates and Jeribe formations are considered as the main targets of the Tertiary petroleum system in the western part of the Zagros Basin. The formations consist of carbonates with some evaporate intercalations of the Dhiban Formation. This study utilized data from a field investigation including newly described outcrop sections and newly discovered productive oil fields within the Kirkuk embayment zone of the Zagros fold and thrust belt such as Sarqala and Kurdamir wells. This work is the first to show a stratigraphic correlation and paleoenvironmental interpretation by investigating both well data and new outcrop data. Three depositional environments were identified, (1) an inner and outer ramp belts environment, (2) shoal environment, and (3) restricted lagoon environment. Within these 3 environments, 12 microfacies were identified, based on the distribution of fauna mainly benthonic foraminifera, rock textures, and sedimentary structures. The inferred shallow water depths and variable salinities in both the Euphrates Formation and Jeribe Formation carbonates are consistent with deposition on the inner ramp (restricted lagoon and shoal) environments. Those found in the Euphrates Formation constrained the depositional environment to the restricted lagoon and shoal environment, while the microfacies in the Jeribe Formation provided evidence for an inner ramp and middle to outer ramp belt environments. This study represents the first detailed research that focuses on the stratigraphic correlation and changes in carbonate facies with the main aim to provide a wider understanding of stratigraphy of these carbonate reservoirs throughout the northern part of Iraq.

Finite Volume Method for Modelling Gas Flow in Shale

Gas flow in shale is a complex phenomenon and is currently being investigated using a variety of modelling and experimental approaches. A range of flow mechanisms need to be taken into account when describing gas flow in shale including continuum, slip, transitional flow and Knudsen diffusion. A finite volume method (FVM) is presented to mathematically model these flow mechanisms. The approach incorporates the Knudsen number as well as the gas adsorption isotherm, allowing different flow mechanisms to be taken into account as well as methane sorption on organic matter. The approach is applicable to non-linear diffusion problems, in which the permeability and fluid density both depend on the scalar variable, the pressure. The FVM is fully conservative, as it obeys exact conservation laws in a discrete sense integrated over finite volumes. The method is validated first on unsteady-state problems for which analytical or numerical solutions are available. The approach is then applied for solving pressure-pulse decay tests and a comparison with an alternative finite element numerical solution is made. Results for practical laboratory pressure-pulse decay tests of samples with very low permeability are also presented.

Investigating the Link between Surface Deformation and Microseismicity Using Coupled Flow-geomechanical Simulation

In this paper, we investigate the relationship between surface deformation and microseismicity using coupled fluid-flow and geomechanical simulation. Since both microseismic and InSAR monitoring integrated with coupled fluid-flow/geomechanical modelling represent cost effective approaches in monitoring the containment of injected CO2, it is worthwhile exploring any potential link between microseismicity and surface deformation. Specifically, we simulate and examine the temporal and spatial evolution of microseismicity (see Angus et al., 2010) and surface uplift due to injection of CO2 for a faulted graben style sandstone reservoir model. We attempt to address whether there is a significant link between surface uplift and microseismicity, and if so, can we draw some relationship between rates of surface uplift and seismicity?

Laboratory Analysis of Shale Permeability

Until recently very few data were available on the permeability of shale samples. Those available were mainly obtained by those interested in top seal capacity, overpressure retention or radioactive waste disposal. The shale gas revolution, which has taken place in the USA over the last decade, has meant that the amount of data available on shale permeability has increased by several orders of magnitude; although it is important to note that “shale” gas reservoirs tend to have far less clay than shale seals to petroleum reservoirs and overpressured compartments. The experimental methods used by those involved in the shale gas industry differ significantly from those involved in seal analysis.