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2015_Fundamentals of Gas Shale Reservoirs(Reza Rezaee)

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Fundamentals oF Gas shale ReseRvoiRs Fundamentals oF Gas shale ReseRvoiRs edited by Reza Rezaee Department of Petroleum Engineering Curtin University Copyright © 2015 by John Wiley and CSIRO Division of Earth Science and Resource Engineering, Perth, WA, Australia Liu, Shaobo, Dr., PetroChina Research Institute of Petroleum Exploration and Development, Beijing, China Pervikhina, Marina, Dr., CSIRO Energy Flagship, Perth, WA, Australia Rasouli, Vamegh, Prof., Department of Petroleum Engineering, University of North Dakota, Grand Forks, ND, USA Rezaee, Reza, Prof., Department of Petroleum Engineering, Curtin University, Perth, WA, Australia Rothwell, Mark, HSEassist Pty Ltd, Perth, WA, Australia Sicking, Charles, Dr., Global Geophysical Services, Inc., Dallas, TX, USA Sigal, Richard F., Dr., Mewbourne School of Petroleum and Geological Engineering, The University of Oklahoma, Norman, OK, USA Slatt, Roger M., Prof., Institute of Reservoir Character­ ization, School of Geology and Geophysics, Sarkeys Energy Center, University of Oklahoma, Norman, OK, USA thorn, terence H., President, JKM 2E Consulting, Houston, TX, USA tian, Hua, Dr., PetroChina Research Institute of Petroleum Exploration and Development, Beijing, China tibi, Rigobert, Dr., Global Geophysical Services, Inc., Denver, CO, USA torcuk, Mehmet A., Dr., Colorado School of Mines, Golden, CO, USA trabucho‐Alexandre, João, Prof., Department of Earth Sciences, University of Durham, Durham, UK; and Institute of Earth Sciences Utrecht, Utrecht University, Utrecht, The Netherlands Xu, Mingxiang, Dr., School of Mining and Petroleum Engineering, University of Alberta, Edmonton, Alberta, Canada Zhang, Shuichang, Dr., PetroChina Research Institute of Petroleum Exploration and Development, Beijing, China The hydrocarbon source from conventional reservoirs is decreasing rapidly. At the same time, global energy con- sumption is growing so quickly that conventional reserves alone cannot solely satisfy the demand. Therefore, there is a pressing need for alternative sources of energy. As things currently stand from a technical viewpoint, the more expen- sive clean‐sustainable energy sources cannot compete with the relatively cheap nonrenewable fossil fuels. Thus, the obvious immediate alternative energy source would be found in non‐conventional oil and gas resources. These non‐ conventional resources come in many forms and include gas hydrate, tar sand, oil shale, shale oil, tight gas sand, coal bed methane, and of course, shale gas. Shale gas has for some time been the focus of gas exploration and production in the USA and in other countries. Based on a recent EIA report, there is an estimated 7299 trillion cubic feet (Tcf) of techni- cally recoverable shale gas resource to be found in some 137 basins located in 41 countries. Following notable successes in shale gas production in the USA, to the point where that country now produces more shale gas than gas from the conventional sources, other countries are pursuing the same course. Even so, in order to be success- ful in the exploration and the development of shale gas plays, a number of important factors have to be taken into account: • A vast knowledge of the different aspects of shales, such as organic geochemistry, mineralogy, petrophysical properties, shale geomechanics, reservoir engineering and so on, is required in order to properly evaluate and map shale gas sweet spots in each sedimentary basin. • Shale gas environmental issues together with chal- lenges such as the high water demands and possible contamination risks posed by hydraulic fracturing fluids and waste have to be addressed. The aim of this book is to provide some guidance on the major factors involved in evaluating shale gas plays. The book is structured as follows: Chapter 1 introduces shale gas from the point of view of its global significance, distribution and inherent challenges. Chapter 2 discusses the environments suitable for organic matter‐rich shale deposition. Chapter 3 assesses the organic geochemical properties of shale gas resource systems. Chapter 4 highlights important points about the sequence stratigraphy of shales. Chapter 5 discusses methods used for evaluating pore geometry in shales. Chapter 6 details the steps required for the petrophysical analysis of shale gas plays. Chapter 7 deals with pore pressure estimation of shales using conventional log data. Chapter 8 covers shale gas geomechanics. Chapter 9 discusses the rock physics of organic‐rich shales. Chapter 10 introduces passive seismic methods for non‐ conventional resource development. Chapter 11 discusses gas transport processes in shale. Chapter 12 reviews the critical issues surrounding the sim- ulation of transport and storage in shale reservoirs. Chapter 13 provides important information about the performance analysis of shale reservoirs. Chapter 14 presents methodologies to determine original gas in place (OGIP), technically recoverable resources (TRR) and the recovery factor (RF) for shale reservoirs. Preface xviii PREFACE Chapter 15 discusses molecular simulation of gas adsorption. Chapter 16 deals with the wettability of gas shale reservoirs. Chapter 17 summarises gas shale challenges expected to occur over the life cycle of the asset. Chapter 18 presents gas shale environmental issues and challenges. The study of shale gas plays is advancing rapidly in many countries, and I hope this book will provide some useful fundamental information on the topic. Professor Reza Rezaee August 7, 2014 Curtin University, Department of Petroleum Engineering Fundamentals of Gas Shale Reservoirs, First Edition. Edited by Reza Rezaee. © 2015 John Wiley although for various reasons many countries face major challenges before the same success in shale gas can be enjoyed as in the United States (Stevens, 2012). As outlined by Ridley (2011), the significance and future of shale gas will also be influenced by the interplay of a wide variety of other issues, including the following: • Potentially falling gas prices, due to increased production • Reduced production costs due to technological developments, and the associated competitiveness of gas produced from shale in comparison to other sources • Increased demand for gas due to increased adoption of natural gas to produce energy and in new markets (i.e., natural gas‐fuelled vehicles) • The regulatory environment for shale gas development in each country 1.4 GLOBAL SHALE GAS RESOURCES This section collates shale gas resource data from a variety of sources. It is structured as follows: • Sources of information • Resource estimation methodologies • TRR data As noted previously, shale gas is widespread within the world’s sedimentary basins. For example, Figure 1.3 (from EIA, 2011b) illustrates that shale gas plays occur in all of the regions assessed within the study of concern. However, it is also known that Russia and the Middle East also have con­ siderable shale gas resources, but are unlikely to develop them in the next decade due to the abundance of conven­ tional gas resources. 1.4.1 Sources of Information For assessing the global resources, this chapter has extracted data from EIA (2011a, b). This source was the primary source of data. However, it does not include data for the Russia or the Middle East. The other source is obtained from Rogner (1997). This source was used to provide resource estimates for Russia and the Middle East. In addition to the above sources, two regional maps pub­ lished by the Society of Petroleum Engineers were referenced, as they both include “shale resource” values. However, the values are identical to those presented by the EIA. These sources provided data for the most significant developed nations globally. It is certain that many other nations will have shale gas resources, but they are currently lacking demand for local production and also lack infra­ structure for distribution and export, and would therefore have difficulty attracting investment. 1.4.2 Resource Estimation Methodologies The different sources of data quote a slightly different category of resource. The resource category framework presented by Dong is used as a baseline for comparing the differing resource estimation techniques associated with various sources. The primary objective was to identify a TRR for each region, including a play‐specific breakdown where avail­ able. This was relatively straightforward for the EIA sources since they quote something very similar to TRR. However, some assumptions were required to convert the values presented by Rogner (1997). It should be noted that TRR includes both economic and uneconomic resources. As such, despite the large TRR values sometimes quoted, it may be uneconomic to produce gas from these resources. 35 History US dry natural gas production trillion cubic feet 2011 Projections 30 25 20 15 10 5 0 1990 1995 2000 2005 2010 2015 Nonassociated onshore Associated with oil Coal bed methane Tight gas Shale gas Nonassociated offshore Alaska 2020 2025 2030 2035 2040 FIGURE 1.2 Historical and projected sources of natural gas in the United States (EIA, 2013). 6 GAS SHALE: GLOBAL SIGNIFICANCE, DISTRIBUTION, AND CHALLENGES 1.4.2.1 EIA Global Resource Estimation Methodology The resource estimates presented by the EIA in the global shale gas review were calculated using a basin‐by‐basin approach, using the following methodology: 1. Conducting preliminary geological and reservoir char­ acterization of shale basins and formation(s) 2. Establishing the areal extent of the major gas shale formations (i.e., specific to certain shale formations within a basin) 3. Defining the prospective area for each gas shale formation 4. Estimating the total gas in‐place (GIP) 5. Estimating the risked shale GIP, accounting for the following: • Play success probability factor • Prospective area success risk factor 6. Calculating the TRR of shale gas in terms of Tcf. On a “by region” average, this value was generally between 24 and 29% of GIP. Naturally, the accuracy of the estimate is a function of the availability and quality of data, but this is generally reflected in the calculation of “risked GIP” and the subsequent calculation of TRR. The TRR values presented by the EIA effectively correlate with the TRR zone defined by Dong et al. (2013). 1.4.2.2 EIA USA Resource Estimation Methodology The resource estimates provided by the EIA for individual US shale gas plays were assessed using a comparable method to that adopted for the global resources assessment. However, the main difference is that production data (i.e., well recovery data) was used to support the estimate. This reflects the fact that many US shale gas plays are in a production phase, with approximately 25,000 producing wells in 2007, (Vidas and Hugman, 2008), whilst the rest of the world is still largely in the exploration phase. The resource estimates quoted represent a TRR for each shale gas play, although they do reduce the gas already pro­ duced. The TRR for this source effectively correlates with the TRR zone defined by Dong et al. (2013). 1.4.2.3 Rogner Resource Estimation Methodology The Rogner study (1997) provides shale gas resource data for Russia and the Middle East. Rogner states that the estimates presented are very speculative as a result of the lack of data. Assessed basins with resource estimate Assessed basins without resource estimate Countries within scope of report Countries outside scope of report Legend FIGURE 1.3 Map of 48 major shale basins in 32 countries (from EIA, 2011b). GLOBAL RESOURCE DATA 7 The estimation methodology involved applying knowledge about US gas shales to other shales in different regions. In simple terms, this involved assuming that all prospective shales contain 17.7 Tcf of gas for every Gt (gigatonne) of shale in‐place. The value presented by Rogner is a GIP estimate, which does not conform to the definition of TRR used by the EIA and defined by Dong et al. (2013). The Rogner GIP estimates were converted to TRR values by averaging the GIP:TRR ratios for global shale gas plays from other sources, then applying this average ratio to the Rogner GIP values. It was also necessary to adjust Rogner Middle East values to account for overlap with EIA sources. 1.5 GLOBAL RESOURCE DATA The shale gas resource data is presented in Appendix A.1. The information is presented as a hierarchy in terms of region, country, basin, and shale play. A summary of each prospective country, and in some cases region, is presented further. This chapter is limited to the general geological reservoir characteristics and a brief summary of the status of exploration or production. All quantitative reservoir properties and characteristics (i.e., TOC, depth, and thickness) are indicative nonweighted averages only, will vary greatly across any one play, and are not representative of the likelihood of commercial shale gas production. However, they do give an indication of the potential resource quality. All information has been sourced from the EIA documen­ tation (2011a, b, c), except where stated otherwise. 1.5.1 China China has two major prospective basins, the Sichuan Basin and the Tarim Basin, with a combined estimated TRR of 1275 Tcf. This is the largest TRR of any single nation within this review and supports the opinion that China is widely regarded as having excellent potential for shale gas development. The four target shales within both basins were deposited on a passive margin in a marine environment from Cambrian to Silurian times. They are thick (200–400 ft), dry gas mature (Ro of 2.0–2.5), and have moderate clay content. However, the shales are situated relatively deep at depths of 10,000– 14,000 ft, and have only moderate organic content (2–3%). Geological complexity is high in certain parts of both basins, which is the reason why large parts of the basin have currently been disregarded in preparing TRR estimates (EIA, 2011b). There is considerable exploration activity in China due to the potential significance in terms of domestic energy supply, less reliance on the Middle East, and high domestic demand for energy. Although there is currently no shale gas production, the Sichuan Basin has a well‐developed network of natural gas pipelines, in addition to proximity to large cities with considerable energy demand. That said, the pro­ spective areas do suffer from remoteness and often a lack of water (UPI, 2013). 1.5.2 The United States The United States has numerous producing shale gas basins, many of which are very well understood due to pro­ duction‐related data. It also has the second largest TRR within this study. A total of 16 basins comprising 20 shale gas plays are noted within the source study, with a cumulative TRR of 751 Tcf. All the prospective shales are of marine origin, with the majority associated with foreland basins (e.g., Appalachian Basin) and Devonian deposition. The majority are of favorable depth, with some as sha
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