CPGE: Unconventional Resources

Tadeusz Patzek (patzek@mail.utexas.edu) is the Program Manager of the Unconventional Resources research program at CPGE.

Research Projects

Deformation Mechanisms in Shale - Hugh Daigle

Successful fracture stimulation is a challenge because some shales do not appear to behave brittlely, failing along discrete planes, but rather fail ductilely, exhibiting distributed deformation and dilation. I believe that much insight into this problem can be obtained by applying critical state soil mechanics to shales instead of treating them as linear-elastic media. As a first step, I plan to perform simple triaxial consolidation and shear tests under drained and undrained conditions to characterize the failure and yield behavior of several different shales. The results of this work can then be used for numerical simulation of well completion and fracture behavior, and represent a fundamental first step towards understanding shale mechanics.
Capillary Inhibition of Methane Hydrate Nucleation - Hugh Daigle

Recent work has shown that methane hydrate prefers to nucleate in the largest pores of the host sediment because this is where the most favorable thermodynamic conditions exist. This can explain the distribution of hydrate observed at many sites worldwide. The role of this capillary inhibition in dynamic systems such as sites with active fracturing and gas production scenarios has not been investigated thoroughly. This work will be conducted with numerical simulations that couple pore-scale processes with macroscale behavior.
Development of Fracture Fluid Additive That Will Enhance Flowback and Recovery From Gas Shales - David DiCarlo and Quoc P. Nguyen

One of the keys for enhancing recovery from gas shales is to maximize the flowback of the fracturing fluid. We propose to develop a surfactant as an additive that can be applied to either water based or CO2 foam fracturing fluids. This additive will act to lower the interfacial tension (IFT) between brine and the gas in place. This will decrease the capillary forces binding the water to the shale, and will increase the water flowback for enhanced gas and condensate recovery.
Novel Concepts of Vapor Oil Gravity Drainage in Fractured Viscous Oil Formation - Quoc P. Nguyen

Vapor oil gravity drainage (VOGD) is an important mechanism of viscous oil recovery in naturally fractured reservoirs where the displacement of matrix oil is challenging. The efficiency of VOGD process in heavy oil reservoirs can be improved by injecting steam to lower oil viscosity and promote thermal expansion of the hydrocarbon phase. The objective of this project is to evaluate experimentally and theoretically the use of unconventional low-cost solvents to improve the performance of the VOGD process at lowest solvent retention with steam injection in fractured viscous oil formations. Novel injection strategies will decrease emissions, allow operations at much lower temperatures than that in the conventional steam processes, and improve both reservoir and wellbore flow performance.
Numerical Simulation of Diagenetic Alteration and its Effect on Residual Gas in Tight Gas Sandstones - Masa Prodanovic and Steven Bryant

The geometry of intergranular pore space in tight gas sandstones (at the porosities less than 10%) differs from conventional reservoir sandstones in some fundamental aspects: the fluid pathways are significantly narrower so that pore body/pore throat aspect ratios are larger, and some percentage of the fluid pathways are closed and disconnect the pore space. This profoundly affects macroscale fluid properties and is the reason for failure of conventional porosity-permeability relationship models. We numerically investigate the influence of cementation of intergranular pore spaces.

For more on these topics, please see the Numerical Simulation of Diagenetic Alteration and its Effect on Residual Gas in Tight Gas Sandstones project summary page.
Fundamentals of Gas Transport in Tight Gas Sandstones and Shales - Steven Bryant in collaboration with Masa Prodanovic, Peter Eichhubl (BEG) and Peter Flemings (BEG)

Several unique characteristics of these rocks are the consequence of post depositional diagenetic processes including mechanical compaction, quartz and other mineral cementation, and mineral dissolution. These processes lead to permanent alteration of the initial pore structure causing an increase in the number of isolated and disconnected pores and thus in the tortuosity. The objective of this research is to develop a pore scale model of the geological processes that create tight gas sandstones and to carry out drainage simulations in these models. These models can be used to understand the flow connections between tight gas sandstone matrix and the hydraulic fractures needed for commercial production rates.

Topics of current interest include:
- Mechanisms of Porosity Reduction
- Physics of Flow in Shales
- Structure of Nanopores in Shales
- Influence of Water on Gas Production
For more on these topics, please see the Fundamentals of Gas Transport in Tight Gas Sandstones and Shales project summary page.
Mechanisms for Forming Methane Hydrates in Petroleum Systems - Steven Bryant in collaboration with Ruben Juanes (MIT)

In the long term, methane hydrates are an interesting potential resource. In the Arctic, hydrate accumulations with large saturations (more than 70% of pore space) are well documented, making the energy density (MCF per unit volume of rock) an order of magnitude greater than in tight gas sandstone or shale gas reservoirs. Similar accumulations exist in sands below sufficiently deep water. We have developed a sedimentological model of a process by which such accumulations may have formed below the permafrost in Arctic regions. Crucially, the model explains why good reservoir sands are often only partially filled with large saturations of hydrate, and why layers containing mostly water often occur between layers of containing hydrate.

For a more complete description, please see the Mechanisms for Forming Methane Hydrates in Petroleum Systems project summary page.
The Barnett Shale in Texas - Tadeusz Patzek

Introduction: By 2011, the unconventional resource plays in the U.S. have become a 300 billion dollar bet about the future of energy supply for our great country. Historically, the Barnett shale in Texas has been the oldest and the largest shale field project in the U.S. and the world. Up to now there have been about 15,000 Barnett shale wells producing gas, condensate and water. Over the years there has been major progress in well and hydrofracture design. All wells drilled since 2004 have been horizontal, with almost one mile long horizontal sections, and 10 or more hydrofracture stages.

Objective: Our role is to provide the scientific and engineering analysis of the long-term feasibility of the unconventional resource bet and propose technological solutions to increase the odds in our favor. In Stage 1 of this Sloan Foundation project, we explore production and geological data from the Barnett shale, and identify best practices in well drilling, completion, and operation. In particular, we examine historical production data and perform a novel more accurate statistical analysis of these data.

For more info, please see the Barnett Shale, Texas page.
Volumetric Rock Damage - Tadeusz Patzek

Introduction: Rock damage is the process of breakage of grain bonds and the initiation and growth of discontinuous microcracks that may coalesce into a fracture. There are a great number of damage models, plasticity models and methods for modeling rock fractures. The available models of fracture growth do not account for microstructural effects in damage accumulation. We are looking at fracture and change of rock properties from microstructural level and using methods of homogenization of heterogeneous materials, we go from local damage model to non-local damage. We also investigate the effect of microstructural length scale of rock in the pattern of damage. This will let us see how fracture grows in reservoir rock as a function of stress state, current damage, temperature, chemical effects and microstructural properties of rock.

Objective: The main objective of this work is the enhancement of hydrocarbon production from tight formations with zero to very low production rates by changing the rock flow properties as the hydrocarbon is produced. Generation of fractures changes the permeability distribution in the rock. In order to calculate the flow rate accurately we need to solve the damage diffusion equation that updates the rock permeability with the progress of damage in time and space.

For more info, please see the Volumetric Rock Damage page.

Questions and Problems

Nanoscale/microscale: How to characterize the rock microstructure and the filaments of organic matter, so that the fluid hydrocarbon storage and rock permeability of mudrocks are correctly captured?
Microscale/mesoscale: What is the connectivity of flow channels of any kind on the scale of centimeters/meters?
Affecting rock microstructure: How to locally manipulate state of stress to increase the rock permeability? How to cause local stress unloading, break rock bonds, and generate/link microcracks and/or microfractures?
Well construction: Given the improved knowledge of rock structure at micro and mesoscale, how can one connect a block of rock to a well, and how can one influence the state of stress in this block from a well?
Drilling and completing wells in mudrock systems: What are the best fluids to use, and what are their benefits and shortcomings?
Well monitoring: How does one monitor in the dynamic state of rock around a wellbore with evolving the well state and controlling it in mind?
Development planning, economics, and risk management: How best to handle uncertainty in all stages of the decision-making process so as to manage risks and optimize production rate and ultimate recovery from unconventional resources?
Rock imaging: How can one image the effects of changes of rock state on hydrocarbon production?
Water management: How to design improved, reliable, and energy-conserving reverse osmosis and membrane processes of produced water purification?
The mechanisms controlling the fracture propagation rates of multiple fracture tips in complex hydraulic fracturing need to be identified. Hydraulic fracturing processes lie in the poorly studied area between critical/dynamic fracture growth and subcritical growth, and as such are probably likely to be highly sensitive to changing chemical and geomechanical in situ environments.
As most unconventional reservoirs contain an abundance of natural discontinuities, fundamental experimental and numerical work are required to enhance the predictability of hydraulic fracture propagation. No currently available commercial model is capable of the realistic simulation of multistranded, non-planar fracture propagation.
Fluid production must be optimized over the life of the well, especially concerning the efficient lift liquids from highly deviated wells through appropriate pump choice and placement.