Preface 1. Basic tools 2. Elasticity and Hooke's law 3. Seismic wave propagation 4. Effective media 5. Granular media 6. Fluid effects on wave propagation 7. Empirical relations 8. Flow and diffusion 9. Electrical properties Appendices.

/pdf/the-rock-physics-handbook-tools-for-seismic-analysis-of-58lw74s1oi.pdf

The Rock Physics Handbook: Tools for Seismic Analysis of Porous Media

https://pangea.stanford.edu/departments/geophysics/dropbox/STRESS/publications/MDZ%20PDF's/2006/2006_Empirical_relations_between_rock_strenght.pdf

Empirical relations between rock strength and physical properties in sedimentary rocks

Extraction of natural gas from shale rock in the United States (US) is one of the landmark events in the 21st century. The combination of horizontal drilling and hydraulic fracturing can extract huge quantities of natural gas from impermeable shale formations, which were previously thought to be either impossible or uneconomic to produce. This review offers a comprehensive insight into US shale gas opportunities, appraising the evolution, evidence and the challenges of shale gas production in the US. The history of US shale gas in this article is divided into three periods and based on the change of oil price (i.e., the period before the 1970s oil crisis, the period from 1970s to 2000, and the period since 2000), the US has moved from being one of the world's biggest importers of gas to being self-sufficient in less than a decade, with the shale gas production increasing 12-fold (from 2000 to 2010). The US domestic natural gas price hit a 10-year low in 2012. The US domestic natural gas price in the first half of 2012 was about $2 per million British Thermal Unit (BTU), compared with Brent crude, the world benchmark price for oil, now about $ 80–100/barrel, or $14–17 per million BTU. Partly due to an increase in gas-fired power generation in response to low gas prices, US carbon emissions from fossil-fuel combustion fell by 430 million ton CO 2 – more than any other country – between 2006 and 2011. Shale gas also stimulated economic growth, creating 600,000 new jobs in the US by 2010. However, the US shale gas revolution would be curbed, if the environmental risks posed by hydraulic fracturing are not managed effectively. The hydraulic fracturing is water intensive, and can cause pollution in the marine environment, with implications for long-term environmental sustainability in several ways. Also, large amounts of methane, a powerful greenhouse gas, can be emitted during the shale gas exploration and production. Hydraulic fracturing also may induce earthquakes. These environmental risks need to be managed by good practices which is not being applied by all the producers in all the locations. Enforcing stronger regulations are necessary to minimize risk to the environment and on human health. Robust regulatory oversight can however increase the cost of extraction, but stringent regulations can foster an historic opportunity to provide cheaper and cleaner gas to meet the consumer demand, as well as to usher in the future growth of the industry.

Natural gas from shale formation – The evolution, evidences and challenges of shale gas revolution in United States

http://home.ustc.edu.cn/~ly2014/Advances_in_Geosciences/Reading%20materials%20for%20Week%202/Group6-Characterisation%20of%20the%20Basel%201%20enhanced%20geothermal%20system.pdf

Characterisation of the Basel 1 enhanced geothermal system

This paper provides a review of the geomechanics and modeling of geomechanics associated with geologic carbon storage (GCS), focusing on storage in deep sedimentary formations, in particular saline aquifers. The paper first introduces the concept of storage in deep sedimentary formations, the geomechanical processes and issues related with such an operation, and the relevant geomechanical modeling tools. This is followed by a more detailed review of geomechanical aspects, including reservoir stress-strain and microseismicity, well integrity, caprock sealing performance, and the potential for fault reactivation and notable (felt) seismic events. Geomechanical observations at current GCS field deployments, mainly at the In Salah CO2 storage project in Algeria, are also integrated into the review. The In Salah project, with its injection into a relatively thin, low-permeability sandstone is an excellent analogue to the saline aquifers that might be used for large scale GCS in parts of Northwest Europe, the U.S. Midwest, and China. Some of the lessons learned at In Salah related to geomechanics are discussed, including how monitoring of geomechanical responses is used for detecting subsurface geomechanical changes and tracking fluid movements, and how such monitoring and geomechanical analyses have led to preventative changes in the injection parameters. Recently, the importance of geomechanics has become more widely recognized among GCS stakeholders, especially with respect to the potential for triggering notable (felt) seismic events and how such events could impact the long-term integrity of a CO2 repository (as well as how it could impact the public perception of GCS). As described in the paper, to date, no notable seismic event has been reported from any of the current CO2 storage projects, although some unfelt microseismic activities have been detected by geophones. However, potential future commercial GCS operations from large power plants will require injection at a much larger scale. For such large-scale injections, a staged, learn-as-you-go approach is recommended, involving a gradual increase of injection rates combined with continuous monitoring of geomechanical changes, as well as siting beneath a multiple layered overburden for multiple flow barrier protection, should an unexpected deep fault reactivation occur.

/pdf/the-geomechanics-of-co2-storage-in-deep-sedimentary-3k6vmdsuf7.pdf

The geomechanics of CO2 storage in deep sedimentary formations

Elasticity . Linear elasticity. Non-linear elasticity. Poroelasticity. Time-dependent effects. Failure mechanics. Basic concepts. The failure surface. Shear failure - Mohr's hypothesis. Failure criteria which depend on the intermediate stress. Representation of experimental data. Extension tests. Post-failure behaviour. The theory of plasticity. Soil mechanics. Failure mechanics of saturated rocks. Anisotropy and rock mechanical failure. Some geological aspects of rock mechanics. Underground stresses. Pore pressure. Rock mechanical properties. Stresses around boreholes, and borehole failure criteria. Stresses around boreholes. Borehole failure criteria. Beyond failure initiation. Acoustic wave propagation in rocks. The wave equation. P- and S-waves. Sound velocities in rocks. Acoustic attenuation in rocks. Biot's theory of acoustic wave propagation. Acoustic anisotropy. Rock mechanics and rock acoustics. Micromechanical models. Grain pack models. Effective medium theories of rocks containing cracks. Fractured rocks. Mechanical properties from laboratory analysis. Core samples for rock mechanical laboratory analysis. Laboratory equipment. Rock mechanical test procedures. Index Tests. Acoustic measurements. Mechanical properties from field data. Estimation of elastic parameters. Estimation of in situ stresses. Estimation of strength parameters. Stability during drilling. Unstable boreholes - reasons and consequences. The principle of a stability analysis. Calculation of minimum mudweight required to prevent borehole collapse. Calculation of maximum mudweight before fracturing. Example calculation. Evaluation of the method and the results. Other aspects of practical importance. Sand prediction. What is sand production? How can sand production be controlled? Mechanisms for sand production. What is sand prediction? Examples of problems to be considered. Modelling for sand prediction. Fracturing. Conditions for tensile failure. Orientation and confinement of fractures. Fracturing pressures. Formation break-down pressures. Determination of fracturing pressures from minifrac tests. Pressures during frac jobs. Fracture gradients in drilling. Reservoir compaction. Subsidence and well problems. Elastic modelling of compaction and subsidence. Consolidation theory. A Consolidation type subsidence model. Laboratory testing for compaction predictions. Numerical modelling of compaction and subsidence. Well Problems associated with compaction. Appendix A. Appendix B. Symbols. Index.

Petroleum Related Rock Mechanics

Publisher Summary The purpose of this chapter is to give an introduction to geological aspects, which are of particular importance in petroleum related rock mechanics. The present state of a rock and its present mechanical properties are of interest. A sedimentary basin may be exposed to sedimentary subsidence, sea-level changes and tectonic forces creating repeated cycles of elevation and depression, in addition to erosion, changes in sedimentary environment, changes in sedimentation rate, solution and precipitation of cementing material etc. All these effects will complicate the geological description of the sedimentary basin. These geological activities and events will affect not only current rock mechanical properties, but also current boundary conditions in terms of in situ stresses and pore pressure. Therefore, knowledge of geological processes is valuable in rock engineering. Although on a totally different time scale and length scale, geological processes are often comparable with events in rock mechanics laboratory testing, which means that such tests may be used to enhance our understanding of geological phenomena.

Chapter 3 Geological aspects of petroleum related rock mechanics

Publisher Summary This chapter discusses basic processes related to hydraulic fracturing. Hydraulic fracturing in rocks takes place when the fluid pressure within the rock exceeds the smallest principal stress plus the tensile strength of the rock. This results in tensile failure or splitting of the rock. A hydraulic fracture may be initiated by natural, geological processes in the earth whereby the fluid pressure increases and/or the smallest principal stress decreases. Artificial or man-made hydraulic fractures in petroleum activities are normally initiated by increasing the fluid pressure in the borehole to the point where the smallest principal stress at the borehole becomes tensile. Hydraulic fracturing has been used commercially as a stimulation technique in the petroleum industry since the early fifties. Finally, this chapter concludes by exploring that, such fracturing jobs are designed to stimulate production from reservoirs with low permeability.

Chapter 11 Mechanics of hydraulic fracturing

Publisher Summary When a well is drilled into a formation, stressed solid material is removed. The borehole wall is then supported only by the fluid pressure in the hole. As this fluid pressure generally does not match the in situ formation stresses, there is stress redistribution around the well. This may lead to deviatoric stresses greater than the formation can support, and failure may result. Knowledge of the stresses around a well is therefore essential for the discussions of well problems. This chapter illustrates that, to examine the stresses in the rock surrounding a borehole, one need to express the stresses and strains in cylindrical coordinates. The hollow cylinder model is a simple example of a borehole in a stressed formation. The model is important in itself, as laboratory tests concerning well stability often are carried out on such samples. Finally, the hollow cylinder model also provides a model for vertical wells through formations where the horizontal stresses are equal.

Chapter 4 Stresses around boreholes. Borehole failure criteria

Effects of currently and previously applied stresses on P- and S-wave velocities in sedimentary rocks (sandstones, chalks, shales) have been studied. Acoustic velocities have been measured on core samples in two orthogonal directions simultaneously under varying (isotropic, anisotropie) conditions of applied stress. Also, a series of model experiments has been performed, where synthetic sandstones were formed under stressed conditions, and where acoustic velocities were measured during and after unloading. The experiments show that the sensitivity to stress generally is largest at low stress levels, in particular below the maximum stress experienced previously. The symmetry of the stress field is to a large extent reflected in the wave propagation. Anisotropic unloading leads to an acoustic anisotropy which remains after the unloading is completed. The results underline that laboratory acoustic measurements should be performed under proper stress conditions. The unloading effect may help to quantify thein situstress field.

A.M. Raaen

Papers

Petroleum Related Rock Mechanics

Chapter 3 Geological aspects of petroleum related rock mechanics

Chapter 11 Mechanics of hydraulic fracturing

Chapter 4 Stresses around boreholes. Borehole failure criteria

Influence of Stress State and Stress History on Acoustic Wave Propagation in Sedimentary Rocks