Unconventional Gas Exploitation Research Articles

Combined Effect of In Situ Stress Level and Bedding Anisotropy on Hydraulic Fracture Vertical Growth in Deep Marine Shale Revealed via CT Scans and Acoustic Emission

The economic exploitation of unconventional gas and oil in deep shale relies closely on effective hydraulic fracturing stimulations. However, the fracturing operations of deep shale reservoirs face challenges of insufficient fracture growth and a rapid decline in productivity due to the increasing in situ stress level. In addition, the shale strata on the margin of the Sichuan Basin are frequently folded and faulted, and the change in bedding inclinations significantly complicates the process of hydraulic fracturing. The investigation of the combined effect of the in situ stress level and bedding anisotropy on the hydraulic fracture configuration is vital for fracturing engineering design. To analyze this, we conducted hydraulic fracturing tests on shale cores to simulate the hydraulic fracture initiation and growth from a horizontally positioned perforation. By using acoustic emission detection and CT scans, the influence of natural stress levels and the angle of the shale’s bedding on the process of hydraulic fracturing in shale and the resulting fracture geometry were analyzed. The results showed that the area of hydraulic fracture under a higher stress level (σ1 = 50 MPa, σ3 = 40 MPa) was about 13%~23% smaller than that created under the lower stress level (σ1 = 30 MPa, σ3 = 20 MPa) when the bedding angle was smaller than 60°. With the increase in bedding angle, the curves of the fracture area and fracture network index under two different stress levels presented similar decreasing trends. Also, the time from micro-crack generation to sample breakdown was significantly reduced when the bedding orientation changed from the horizontal to vertical position. The increasing stress level significantly increased the breakdown pressure. In particular, the fracturing of shale samples with bedding angles of 0° and 30° required a higher fluid pressure and released more energy than samples with larger bedding inclinations. Additionally, the measurement of the sample radial deformation indicated that the hydraulic fracture opening extent was reduced by about 46%~81% with the increasing stress level.

CH4 transport in micro–nano porous media associated with supercritical CO2 flooding

Injecting supercritical CO2 into tight gas reservoirs to displace CH4 is an extremely promising technology of unconventional gas exploitation. However, Darcy's law cannot describe the gas flow due to ultra-low permeability and micro–nano porosity of tight rock. The present work is an analytical approach to investigating the nonlinear seepage characteristics of CH4 displacement by supercritical CO2. Moreover, considering the steady and unsteady state conditions, mathematical models for planar linear flooding, planar radial flooding, and single well and one-well injection/one-well production types are presented, computed, and verified. Their equipotential and streamline charts are first determined by implementing the model. Additionally, by investigating variables such as formation pressure, producing pressure drop, permeability, temperature, well spacing, and mass flow, their contributions to gas production rate are determined. Finally, an approach for improving the gas recovery efficiency is obtained based on the obtained results.

Detonation of a nitromethane-based energetic mixture driven by electrical wire explosion

The combination of energetic material (EM) and an electrical wire explosion (EWE) is an important way to achieve effective release and conversion of electrical and chemical energy, e.g. by generating strong underwater shock waves (SWs) that can be used for dynamic reservoir fracturing in unconventional gas exploitation. This letter proposes a mud-like EM composed of nitromethane, aluminium and copper oxide powder, which can be detonated directly by a tungsten wire explosion. The detonation and successive deflagration result in notably enhanced SWs: with 2.8 g EM, the SW amplitude, impulse and energy are respectively increased by 1.7, 2.1, and 7.9 times compared to an optimal underwater EWE. A direct thermal initiation mechanism for the detonation process is proposed, with the exploding wire, the Joule heating along the current path in the EM and the Al/CuO thermite reaction all serving as heat sources. It is found that the Joule heating and chemical reactions reinforce each other, which is likely the key to the ‘easy’ detonation of nitromethane.

Unconventional Gases Between the Environmental and Energy Crises

The sudden advancement in the technology of unconventional gas production, especially in the United States, has aroused the interest of those interested in energy affairs, as this technical progress allowed greater economic contact with the supply of conventional natural gas, especially with the achievement of large-scale production of unconventional gas pools. In spite of what the technological developments of that industry promise to advance its place in unconventional gas, and the economic effects that it can have, especially with the development of discoveries of its resources over time, on both energy producers and importers. However, opinions were divided between opponents and supporters of its exploitation, whether due to its economic effects. Especially since its exploitation will give many countries the opportunity to give up or reduce dependence on natural gas, especially the United States of America, China and the countries of the European Union; The matter will also negatively affect the countries producing natural gas due to the economic impacts resulting from the expansion of production of that alternative. Or because of its environmental impacts resulting from its use as a fossil fuel, or the technology used in its extraction and production and its harmful effects on water resources and land. This issue will be addressed by seeking to determine the effects resulting from the expansion of unconventional gas production, and whether the exploitation of unconventional gas gives satisfactory economic results that justify the cost that will be borne by society, and the question and what effects this type of energy can have. Through a research plan consisting of an introductory topic entitled What are non-conventional gases, the first topic titled Motives for Expansion in the Production of Non-Conventional Gases, the Second Study entitled the Importance of Non-Conventional Gases and the Controversy Around them, the Third Study entitled “Non-conventional Gas Production and the Strategy of Advanced Countries for Energy Security, Conclusion, Conclusions and recommendations.

التوسع فی انتاج الغازات غیر التقلیدیة حل لأزمة الطاقة أم تفاقم للمشکلة البیئیة

تعتبر الطاقة عنصرا رئيسيا في عملية التنمية الاقتصادية، ويؤدي العمل على خفض تکلفتها أو دعمها إلى التوسع في العملية الإنتاجية وازدهار النشاط الاقتصادي، ومع تقلبات أسعار مصادر الطاقة الاحفورية التي تواجه الدول المستوردة للطاقة کان هناک درس مهم يجب الاستفادة منه من وهو ضرورة تنويع مصادر الطاقة، والسعي نحو تحسين کفاءة الطاقة، و الاستعداد لاستيعاب درجة عالية من تقلب أسعارها، والتقليل من احتمال حدوث صدمات في المستقبل، إضافة إلى الحاجة لاستمرار التنمية الاقتصادية بزيادة المعروض من الطاقة الذي يقابل الطلب عليها بوصفها المحرک للعملية الاقتصادية. وقد اثار التقدم المفاجئ في تقانة انتاج الغاز غير التقليدي وخاصة في الولايات المتحدة اهتمام المهتمين بشئون الطاقة، حيث سمح ذلک التقدم التقني بتواصل اقتصادي أکبر مع امدادات الغاز الطبيعي التقليدي خاصة مع تحقيق إنتاج واسع النطاق لتجمعات الغاز غير التقليدي. وعلى الرغم من ما تبشر به التطورات التکنولوجية لتلک الصناعة بترقي مکانه الغاز غير التقليدي، والتاثيرات الاقتصادية التي يمکن أن يحدثها خاصة مع تطور اکتشافات موارده مع مرور الزمن على منتجي ومستوردي الطاقة على حدا سواء. الا أن الأراء انقسمت بين معارض ومساند لإستغلاله سواء لأثاره الاقتصادية؛ خاصة وأن استغلاله سيمنح الکثير من الدول فرصة التخلى أو التخفيض من الاعتماد على الغاز الطبيعي ، لاسيما الولايات المتحدة الامريکية والصين ودول الاتحاد الأوربي؛ کما سينعکس الأمر بشکل سلبي على الدول المنتجة للغاز الطبيعي بسبب التأثيرات الاقتصادية الناتجة عن التوسع في انتاج ذلک البديل. أو بسبب آثاره البيئية الناتجة عن استخدامه کوقود الأحفوري، أو تقنية المستخدمة في استخراجه وانتاجه و آثارها الضارة على الموارد المائية والأراضي . وسيتم تناول ذلک الموضوع من خلال السعى نحو تحديد الآثار الناتجة من التوسع في إنتاج الغاز غير التقليدي ، وعما إذا کان استغلال الغاز غير التقليدي يعطي نتائج اقتصادية مرضية تبرر التکلفة التي سيتحملها المجتمع، والتساؤل وما الاثار التي يمکن ان يخلفها هذا النوع من مصادر الطاقة. من خلال خطة بحثية تتکون من مبحث تمهيدي بعنوان ماهية الغازات غير التقليدية ، مبحث أول بعنوان دوافع التوسع في انتاج الغازات غير التقليدية، مبحث الثاني بعنوان أهمية الغازات غير التقليدية والجدل حولها، مبحث الثالث بعنوان انتاج الغازات غير التقليدية واستراتيجية الدول المتقدمة لأمن الطاقة، خاتمة، الاستنتاجات والتوصيات. Energy is a key element in the process of economic development, and work to reduce its cost or support it leads to an expansion of the productive process and the prosperity of economic activity, and with the fluctuations in prices of fossil energy sources facing energy importing countries, there was an important lesson that should be taken advantage of, which is the need to diversify energy sources, And the pursuit of improving energy efficiency, and willingness to absorb a high degree of price volatility, and reduce the possibility of future shocks, in addition to the need for continued economic development by increasing the supply of energy that meets the demand for it as the engine of the economic process. The sudden advancement in the technology of unconventional gas production, especially in the United States, has aroused the interest of those interested in energy affairs, as this technical progress allowed greater economic contact with the supply of conventional natural gas, especially with the achievement of large-scale production of unconventional gas pools. In spite of what the technological developments of that industry promise to advance its place in unconventional gas, and the economic effects that it can have, especially with the development of discoveries of its resources over time, on both energy producers and importers. However, opinions were divided between opponents and supporters of its exploitation, whether due to its economic effects. Especially since its exploitation will give many countries the opportunity to give up or reduce dependence on natural gas, especially the United States of America, China and the countries of the European Union; The matter will also negatively affect the countries producing natural gas due to the economic impacts resulting from the expansion of production of that alternative. Or because of its environmental impacts resulting from its use as a fossil fuel, or the technology used in its extraction and production and its harmful effects on water resources and land. This issue will be addressed by seeking to determine the effects resulting from the expansion of unconventional gas production, and whether the exploitation of unconventional gas gives satisfactory economic results that justify the cost that will be borne by society, and the question and what effects this type of energy can have. Through a research plan consisting of an introductory topic entitled What are non-conventional gases, the first topic titled Motives for Expansion in the Production of Non-Conventional Gases, the Second Study entitled the Importance of Non-Conventional Gases and the Controversy Around them, the Third Study entitled “Non-conventional Gas Production and the Strategy of Advanced Countries for Energy Security, Conclusion, Conclusions and recommendations.

Super cycles in natural gas prices and their impact on Latin American energy and environmental policies

There was an upward trend in energy commodity prices since 2000, but with the surge in supply coming from unconventional oil and gas resources in North America, the trend in natural gas prices has become downward in recent years. However, the exploitation of these resources is generating public concerns due to the possible adverse environmental impacts of using hydraulic fracturing and other techniques on underground water. The purpose of this paper is to address the following questions: are there super cycles in natural gas prices? What are the environmental consequences in Latin America of the exploitation of unconventional gas given the cyclical behavior of gas prices? How are the governments in the region implementing energy and environmental policies to regulate unconventional shale gas production? With the last peak occurring in 2006, we identified three super cycles in natural gas prices, and it is predicted to observe a new super cycle in the 2020s. Our analysis indicates that the unstable political situation, the institutional weakness, the governmental intervention through asset nationalization, high capital expenditures to develop LNG export projects and to explore shale resources, as well as the pre-salt discoveries in Brazil make uncertain that the shale gas boom achieve a significant impact in Latin America during the coming gas-price super cycle.

Numerical Study of Simultaneous Multiple Fracture Propagation in Changning Shale Gas Field

Recently, the Changning shale gas field has been one of the most outstanding shale plays in China for unconventional gas exploitation. Based on the more practical experience of hydraulic fracturing, the economic gas production from this field can be optimized and gradually improved. However, further optimization of the fracture design requires a deeper understanding of the effects of engineering parameters on simultaneous multiple fracture propagation. It can increase the effective fracture number and the well performance. In this paper, based on the Changning field data, a complex fracture propagation model was established. A series of case studies were investigated to analyze the effects of engineering parameters on simultaneous multiple fracture propagation. The fracture spacing, perforating number, injection rate, fluid viscosity and number of fractures within one stage were considered. The simulation results show that smaller fracture spacing implies stronger stress shadow effects, which significantly reduces the perforating efficiency. The perforating number is a critical parameter that has a big impact on the cluster efficiency. In addition, one cluster with a smaller perforating number can more easily generate a uniform fracture geometry. A higher injection rate is better for promoting uniform fluid volume distribution, with each cluster growing more evenly. An increasing fluid viscosity increases the variation of fluid distribution between perforation clusters, resulting in the increasing gap between the interior fracture and outer fractures. An increasing number of fractures within the stage increases the stress shadow among fractures, resulting in a larger total fracture length and a smaller average fracture width. This work provides key guidelines for improving the effectiveness of hydraulic fracture treatments.

Economic effects in the UK periphery from unconventional gas development: Evidence from Wales

The paper examines the potential regional economic benefits of the development of unconventional gas. Wales (UK) represents an interesting lens through which to examine the expected effects of unconventional gas developments. In spite of significant resource endowments the region has found it difficult to internalise the economic benefits from prior energy developments. We examine whether possible commercial exploitation of unconventional gas in Wales will be any different from recent rounds of resource and energy investment. We address the challenges for resource peripheries in embedding economic activity linked to unconventional gas and show that there are dangers in generalising economic impact evidence from other states.

Unconventionally contentious: Frack Free South Africa’s challenge to the oil and gas industry

Exploration applications that could lead to unconventional gas exploitation in large parts of South Africa have encountered sustained opposition by social movements. This article looks into Frack Free South Africa's (FFSA) challenges to the government-supported development strategy of shale gas as a supposed means to create jobs and ensure energy autonomy. Adding to discussions in social movement scholarship this article contributes by exploring political, spatial and organizational opportunities afforded by FFSA's activist campaign. The article concludes that in order to grow the movement needs to embrace more inclusive campaign strategies.

Activity concentrations of 238U and 226Ra in two European black shales and their experimentally-derived leachates

The production of gas from unconventional resources became an important position in the world energy economics. In 2012, the European Commission's Joint Research Centre estimate 16 trillion cubic meters (Tcm) of technically recoverable shale gas in Europe. Taking into account that the exploitation of unconventional gas can be accompanied by serious health risks due to the release of toxic chemical components and natural occurring radionuclides into the return flow water and their near-surface accumulation in secondary precipitates, we investigated the release of U, Th and Ra from black shales by interaction with drilling fluids containing additives that are commonly employed for shale gas exploitation.We performed leaching tests at elevated temperatures and pressures with an Alum black shale from Bornholm, Denmark and a Posidonia black shale from Lower Saxony, Germany. The Alum shale is a carbonate free black shale with pyrite and barite, containing 74.4 μg/g U. The Posidonia shales is a calcareous shale with pyrite but without detectable amounts of barite containing 3.6 μg/g U.Pyrite oxidized during the tests forming sulfuric acid which lowered the pH on values between 2 and 3 of the extraction fluid from the Alum shale favoring a release of U from the Alum shale to the fluid during the short-term and in the beginning of the long-term experiments. The activity concentration of 238U is as high as 23.9 mBq/ml in the fluid for those experiments. The release of U and Th into the fluid is almost independent of pressure. The amount of uranium in the European shales is similar to that of the Marcellus Shale in the United States but the daughter product of 238U, the 226Ra activity concentrations in the experimentally derived leachates from the European shales are quite low in comparison to that found in industrially derived flowback fluids from the Marcellus shale. This difference could mainly be due to missing Cl in the reaction fluid used in our experiments and a lower fluid to solid ratio in the industrial plays than in the experiments due to subsequent fracking and minute cracks from which Ra can easily be released.

Mechanism and control factors of water blocking in tight sandstone gas reservoir

The tight sandstone gas reservoirs play an important part in unconventional gas exploitation and development. Nevertheless, the reservoir is very susceptible to water blocking damage in drilling, completion, stimulation and production because of its characteristics. Scholar’s researches pay more attention to the change of permeability before and after the water blocking damage, but the microscopic mechanism of water invasion is little studied. With deepening the cognition of water blocking mechanism, based on the low-permeability tight sandstone reservoir cores of Bashijiqike formation in Keshen J block, the water blocking damage process is evaluated with optimized experiment (spontaneous imbibitions and water flowback) considering the actual reservoir characteristics, MRI and NMR T2 spectra technique is creative used to analysis the water phase invasion process, and the control factors about residual water is discussed. Some conclusions have drawn from that analysis. First of all, the water phase invasion with different initial water saturation is characterized by NMR T2, the smaller pore is occupied by initial water saturation, water phase invasion usually occur in bigger pore with T 2>100 ms and saturated at S w =45%–60%. Moreover, the water phase invasion process among different permeability cores and fractured core is comparison analyzed. The spontaneous imbibitions rate in the core ( K K >0.1 mD). And the water saturates the fracture fast, diffuses from fracture to matrix next. Finally, the rock physical property, fracture, initial water saturation, production pressure, the salinity of intrusive fluid and clay minerals are important factors control the water blocking damage. This paper deepening the cognition of water blocking mechanism in tight sandstone , also perfected the control factors of water blocking damage, and it will be of great importance to the exploration and development of tight sandstone gas reservoirs.

Characterizing the variability in chemical composition of flowback water – results from laboratory studies

The large volumes and unknown composition of flowback and produced waters cause public concerns about the environmental and social compatibility of hydraulic fracturing and the exploitation of unconventional gas. Flowback and produced waters contain not only residues of fracking additives but also chemical species that are dissolved from the shales. Interactions of different shales with an artificial fracturing fluid were studied in lab experiments under ambient and elevated temperature and pressure conditions. Fluid-rock interactions change the chemical composition of the fracturing fluid and this indicates that geochemistry of the fractured shale needs to be considered to understand flowback water composition.

Quantitative Survey and Structural Classification of Hydraulic Fracturing Chemicals Reported in Unconventional Gas Production.

Much interest is directed at the chemical structure of hydraulic fracturing (HF) additives in unconventional gas exploitation. To bridge the gap between existing alphabetical disclosures by function/CAS number and emerging scientific contributions on fate and toxicity, we review the structural properties which motivate HF applications, and which determine environmental fate and toxicity. Our quantitative overview relied on voluntary U.S. disclosures evaluated from the FracFocus registry by different sources and on a House of Representatives ("Waxman") list. Out of over 1000 reported substances, classification by chemistry yielded succinct subsets able to illustrate the rationale of their use, and physicochemical properties relevant for environmental fate, toxicity and chemical analysis. While many substances were nontoxic, frequent disclosures also included notorious groundwater contaminants like petroleum hydrocarbons (solvents), precursors of endocrine disruptors like nonylphenols (nonemulsifiers), toxic propargyl alcohol (corrosion inhibitor), tetramethylammonium (clay stabilizer), biocides or strong oxidants. Application of highly oxidizing chemicals, together with occasional disclosures of putative delayed acids and complexing agents (i.e., compounds designed to react in the subsurface) suggests that relevant transformation products may be formed. To adequately investigate such reactions, available information is not sufficient, but instead a full disclosure of HF additives is necessary.

Shale productivity prediction and fracturing optimization based on compositional simulation

The reserves of unconventional gas, such as shale and tight gas, is enormous in China. The exploitation of unconventional gas is of significance to secure our nation’s energy future. Precise simulation and prediction of gas flowing behavior in such formations is the key to economic efficiency of exploitation. Different from conventional formations, in shale exist slip flow and gas adsorption. To accurately simulate gas flow in shale, we developed a compositional model based on the hybrid grid which is mainly composed by unstructured PEBI (Perpendicular Bisection) grids. Upon this model, the effects of gas composition, adsorption and slip flow on gas production are analyzed. Horizontal well fracturing in a shale gas reservoir is optimized with the help of this model. The results show that the production of shale gas increases rapidly with the number and effective half-length of fractures, and reaches a plateau when they get large or long enough. Therefore, in order to achieve the maximum economic efficiency, the fracture quantity and effective half-length should be reasonably designed.

Valoración socioeconómica de la extracción de gas mediante fracturación hidráulica en la Región de Murcia

La extracción de gas no convencional mediante fracturación hidráulica (fracking) es una técnica controvertida, ya que a sus beneficios sociales y económicos se contraponen sus potenciales riesgos ambientales y sobre la salud humana. En el norte de la Región de Murcia, al igual que en otras zonas de España, se han concedido recientemente permisos de investigación y prospección para la posible explotación de yacimientos gas mediante fracking, lo que ha originado la aparición de movimientos ciudadanos que abogan por su prohibición. El objetivo central de este trabajo es estudiar el conocimiento, la percepción y la aceptabilidad que tienen los ciudadanos de la Región de Murcia sobre la explotación de esta fuente de energía. Con este fin se realiza una encuesta en la que se implementa el método de la Valoración Contingente. Los resultados informan, entre otros, que algo más de dos tercios de la población estarían a favor de su implementación, condicionado a que salud y el medioambiente sean salvaguardados. A su vez cada familia murciana se muestra dispuesta a contribuir, en media, con 15 €/año como sobrecoste en el recibo eléctrico para evitar o retrasar la explotación

Combined Finite-Discrete Element Method for Simulation of Hydraulic Fracturing

Hydraulic fracturing is widely used in the exploitation of unconventional gas (such as shale gas).Thus, the study of hydraulic fracturing is of particular importance for petroleum industry. The combined finite-discrete element method (FDEM) proposed by Munjiza is an innovative numerical technique to capture progressive damage and failure processes in rock. However, it cannot model the fracturing process of rock driven by hydraulic pressure. In this study, we present a coupled hydro-mechanical model based on FDEM for the simulation of hydraulic fracturing in complex fracture geometries, where an algorithm for updating hydraulic fracture network is proposed. The algorithm can carry out connectivity searches for arbitrarily complex fracture networks. Then, we develop a new combined finite-discrete element method numerical code (Y-flow) for the simulation of hydraulic fracturing. Finally, several verification examples are given, and the simulation results agree well with the analytical or experimental results, indicating that the newly developed numerical code can capture hydraulic fracturing process correctly and effectively.

Feasibility Analysis of Groundwater Abstraction for Gas Shale Fracturing in the Lublin Basin (Eastern Poland) / Ocena Możliwości Poboru Wód Podziemnych Do Szczelinowania Łupków Gazonośnych W Basenie Lubelskim (Wschodnia Polska)

Abstract Natural gas extraction from shale rock necessitates hydraulic fracturing of rocks, which involves large amounts of fracture fluids made of 90.5% of water. The authors focus on feasibility of groundwater abstraction for the purpose of applying fracture fluids in wells of the Lublin Basin - area of perspective unconventional gas exploitation from the Ordovician and the Silurian shales. These data refer to the expected specific capacity of wells abstracting groundwater from main useful aquifers. Specific capacity of a well (q) belongs to high-certainty empirical parameters, characterizing water-bearing capacity of rocks at a regional scale. The spatial evaluation of q was based on respective data coming from 7 sheets of the Hydrogeological Map of Poland (scale 1:200,000) covering research area. Specific capacity q was calculated for wells abstracting water from the Upper Cretaceous, Tertiary and Quaternary aquifers in areas presented on particular sheets of the map. Authors determined the variability distribution and the cumulative probability plots of q values, indicating a range which corresponded to a sum of standard deviation (SD) above and below median (X̄), i.e. X̄ ± 1SD. On the total the interval included 68.2% of data. The results reveal that 0.6 ≤ q ≤ 40 m3h-1 per 1 meter of drawdown for the Upper Cretaceous rocks in the eastern part of the area, and 1.1 ≤ q ≤ 110 m3h-1 per 1 meter in the western part, being a result of more intense fracturing and fissuring. Owing to the scarcity of data, q values of wells screened at the Tertiary and Quaternary aquifers are given jointly for the whole area: 0.8 ≤ q ≤ 20 and 1.0 ≤ q ≤ 10 m3h-1 per 1 meter, respectively. The obtained specific capacities are high. When the wells are properly designed, their discharges may reach about ca. 100 m3h-1.

A Semianalytical Forecasting Method for Unconventional Gas and Light Oil Wells: A Hybrid Approach for Addressing the Limitations of Existing Empirical and Analytical Methods

Summary The rapid pace of exploitation of unconventional gas and light oil plays in North America has necessitated the development of new production-forecasting methodologies to aid in reserves assessment, capital planning, and field optimization. The generation of defendable forecasts is challenged not only by reservoir complexities but also by the use of multifractured horizontal wells (MFHWs) for development. In this work, a semianalytical method (SAM) is developed to provide a solid theoretical basis for forecasting. The technique is analytical in that it uses the methods of Agarwal (2010) to calculate contacted oil in place and contacted gas in place (COIP/CGIP) from production rates, flowing pressures, and fluid properties. The rate-normalized pressure (RNP) derivative (RNP′) is a key component of the calculation; pseudopressure is used for gas cases. The technique is also empirical in that an empirical function is fitted to the resulting COIP/CGIP curve vs. time. Although the method is flexible enough that any equation can be used to represent the COIP/CGIP curve, and hence, the sequence of flow regimes exhibited by MFHWs, the equation must be capable of being integrated to allow the extraction of RNP. The stabilized COIP/CGIP during boundary-dominated flow (BDF) must be specified for forecasting—thereafter, the method uses a material-balance simulator to model BDF. Hence, if the well is still in transient flow, a range in forecasts may be generated, depending on the assumed stabilized COIP/CGIP. The new SAM addresses some of the current limitations of empirical and fully analytical (modeling) approaches. Empirical methods, which have been adapted to account for long transient and transitional flow periods associated with ultralow-permeability reservoirs, lack a theoretical basis, and therefore input parameters may be difficult to constrain. However, empirical methods are simple to apply and require a minimum amount of data for forecasting. Analytical models, while representing the physics better, nonetheless require additional reservoir and hydraulic-fracture data that may not be available on every well in the field. The SAM proposed herein is intended to bridge the gap between empirical and modeling-based approaches—it is more rigorous than purely empirical methods, while requiring a lesser amount of data than fully analytical techniques. The new method is tested against simulated and field cases (tight oil and shale gas). Although a simple power-law function is used in the current work to represent the COIP/OGIP curve, which appears adequate for the cases studied, one should note that wells exhibiting long transitional flow periods (e.g., elliptical/radial) will likely require a different functional form.

Shale and tight gas in Poland—legal and environmental issues

Exploitation of unconventional gas is limited by a number of economic, legal, environmental and social factors. When it comes to Poland, legal and environmental factors are of special importance, as they might significantly impact the exploitation of both tight gas and shale gas.Exploitation of unconventional gas deposits, because of the technology needed for opening of these deposits, has relatively great impact on the balance sheet and the quality of water. Polish water resources are limited and depend on time and local circumstances. Therefore, obtaining adequate amounts of water needed to hydraulic fracturing of unconventional gas reservoirs may cause some problems. Another problem is return water management. Injection of contaminated water into the rockmass on a large scale seems to be impossible in Poland. Water discharge to surface waters, which seems to be the most probable solution, would result in deterioration of the purity of Polish rivers.Around 32% of Poland is covered by different forms of protection, which might include limitations in exploitation of hydrocarbon deposits (depending on the type of area).Exploration, documentation and exploitation of unconventional gas in Poland is regulated mainly by the laws and regulations regulating geological and mining activities, environmental protection and waste management.

Environmental and Economic Significance and Feasibility Analysis of Tight Sand Gas Reservoir in China

Currently, with a sharp increase in demand for natural gas and a strict energy supply circumstances, the development of tight sand gas becomes a pressing need for the rapid development of Chinas society and economy. At the end of 2010, the reserves and annual production of tight sand gas in China accounted for 39.2 percent and 24.6 percent of national natural gas, respectively, and the proportions are expected to increase. Compared with other unconventional gas such as shale gas and coal bed methane, the techniques of tight sand gas are relatively mature and development costs of it are relatively low. So tight sand gas should be considered in priority in the exploration and exploitation of unconventional gas in China. The total reserves of tight sand gas in China are 12 trillion cubic meters. Tight sand gas in China possesses the rich reserves and enormous potential to develop, which can ease the current shortage of energy. Besides, China has mastered a series of key techniques such as the well drilling and completion protection supporting technique; well completion and staged fracturing technique of horizontal well, which guarantees the technical feasibility of the development of tight sand gas reservoirs. From the perspective of market, social and environmental meaning, reserves, technique and economic feasibility, this paper presents a systematical analysis about the importance of developing tight sand gas in China.