Marcellus has been development for more than a decade with the application of multi-staged hydraulically fractured horizontal well technology. The technology requires pumping large amount of fracture-fluids and proppant into the target formation at high pressure. The fracture-fluid will then be recovered as aqueous phase during the flowback periods after well shut-in, which can be treated and reused. Sweet spot identification and efficient fracture-fluid flowback management are keys requirement for sustainable and economic development of Marcellus Shale, which can be benefited greatly by optimizing drilling and completion practices, including accurate fracture-fluids flowback prediction. In this work, a systematic study of the geology and engineering factors that influence fracture-fluids flowback, water production, and gas recovery was developed. The complex correlations between gas production and fracture-fluids flowback and produced water provide more understanding about flow mechanism in shale gas. The results suggest that the numbers of hydraulic fracturing stages and well lateral length have significant influence on gas production. The shut-in time and injected proppant volume have the most influence on fracture-fluids flowback. The correlations between gas and fracture-fluid flowback and produced water were different under certain geological conditions and time periods. These knowledges from previous results were used to develop economic analysis regional scale.This work not only will provide the new insights about shale gas well production and fracture-fluid flowback, but also provide a new idea for how to effectively analyze limited field recorded data and to identify the true story behind data.

Water that is produced from shale gas wells in three months after stimulation treatments and shut-in periods is called flowback water. Volume and salt concentrations of flowback water depend on geology, drilling and completions, stimulation and flowback operations. Recent studies include evaluations of geochemical origins based on the compostition concentrations, flowback sampling analysis and numerical studies. However, an in-depth understanding of chemical compositions as well as the changes of compositions is still needed. In this work, we will firstly review the literature related to flowback in shale gas wells to fully understand the chemistry, geochemistry, and physics governing a fracture treatment, shut-in, and flowback. We will then gather all public and in-house flowback data, termed 3-week or 3-month flowback in this work, to build a flowback compositional database. After data screening, we will then analyze this compositional database which would potentially affect the wasterwater treatment design by using four different methods: geographical, changes over time, linear regression, clustering and multi-variable analysis. New understandings such as the magnitude and prevailing trends of concentrations for target constituents as well as the correlations among flowback compositions, the differentiation between early and late time flowback water were obtained and explained on the basis of geochemistry and physics.

Hydraulic Fracturing in Unconventional Reservoirs: Theories, Operations, and Economic Analysis, Second Edition, presents the latest operations and applications in all facets of fracturing. Enhanced to include today's newest technologies, such as machine learning and the monitoring of field performance using pressure and rate transient analysis, this reference gives engineers the full spectrum of information needed to run unconventional field developments. Covering key aspects, including fracture clean-up, expanded material on refracturing, and a discussion on economic analysis in unconventional reservoirs, this book keeps today's petroleum engineers updated on the critical aspects of unconventional activity. - Helps readers understand drilling and production technology and operations in shale gas through real-field examples - Covers various topics on fractured wells and the exploitation of unconventional hydrocarbons in one complete reference - Presents the latest operations and applications in all facets of fracturing

Concern over natural gas extraction across the U.S. and particularly from the Marcellus Shale formation, which underlies approximately two-thirds of the state of Pennsylvania, has been growing in recent years as natural gas drilling activity has increased. Identifying sources of concern and risk from shale gas development, particularly form the hydraulic fracturing process, is an important step in better understanding sources of uncertainty within the industry. Hydraulic fracturing is a well stimulation technique used in the production of natural gas from shale. While hydraulic fracturing has been in use for decades as a method for oil and gas recovery, recent advances in horizontal drilling techniques and fracturing fluid production have made previously unattainable natural gas reservoirs accessible and economically recoverable. In the years after hydraulic fracturing came into widespread use in Pennsylvania, a large amount of data on flowback characteristics became available due to public and regulatory attention to the process. Chapter 3 examines and analyzes the constituents that make up flowback waters collected from drilling sites in the states of Pennsylvania, New York, and West Virginia. Flowback sampling data were collected from four different sources and compiled into one database with a total of 35,000 entries. Descriptive statistical analysis revealed high concentrations of chlorinated solvents, disinfectants, dissolved metals, organic compounds, radionuclides and TDS. Relative prioritization scores were developed for 58 constituents by dividing observed mean concentrations by the Maximum Contamination Level (MCL) guidelines for drinking water. The following constituents were found to have mean concentrations over 10 times greater than the MCL: Barium, Benzene, Benzo(a)pyrene, Chloride, Dibromochloromethane, Radium, and Thallium. Regulatory inspection and violation reports also provide insight into the impact of natural gas extraction on the surrounding environment, human health, and public safety. Inspection reports for natural gas wells in Pennsylvania were collected from the Pennsylvania DEP Compliance Report from 2000 to 2014. Logistic regression analysis of 215,444 inspection records for 70,043 conventional and unconventional wells was conducted in order to compare the odds of violations occurring under different circumstances. The results in Chapter 4 revealed that, when inspected, conventional wells had 40% higher odds of having a violation, but unconventional wells had higher odds for environmental violations related to waste discharge as well as cementing and casing failures. From there, a list of twelve failure scenarios of concern was developed focusing on specific events that may occur during the shale gas extraction process involving an operational failure or a violation of regulations to identify and prioritize potential failure scenarios for natural gas drilling operations through an elicitation of people who work in the industry. Illegal dumping of flowback water, while rated as the least frequently occurring scenario, was considered the scenario least protected by safety controls and the one of most concern to the general public. In terms of worker safety, the highest concern came from improper or inadequate use of personal protective equipment. While safety guidelines appear to be highly protective regarding PPE usage, inadequate PPE is the most directly witnessed failure scenario. Spills of flowback water due to equipment failure are of concern both in regards to the welfare of the general public and worker safety as they occur more frequently than any other scenario examined in this study. In Chapter 6 of this study, the flowback data collected and the violation and failure scenario analyses conducted are used to develop potential exposure scenarios to wastewater from shale gas development. A risk assessment of occupational and residential exposure pathways to flowback water as carried out. Constituents of concern in flowback water were identified from the previous prioritization. The occupational cancer risk estimate for median concentrations did not exceed the target lifetime cancer risk of 10-6 except for benzo(a)pyrene, which exceeds the target risk level even at the 2.5 percentile value. The upper limit of cancer risk form exposure to heptachlor also exceeds 10-6 in this model. Hazard quotient for barium in the same model exceeds 1 (1.7) and results in a total hazard index of 2. The residential risk assessment revealed that several carcinogenic compounds found in flowback water exceed target limits and significantly increase the risk of an individual developing cancer following chronic exposure. In general, exposure from the dermal pathway posed the greatest risk to human health. Considering non-carcinogenic effects, only barium and thallium exceed target limits, where the ingestion pathway seems to be of greater concern than dermal exposure. Exposure to radionuclides in flowback water, particularly through the inhalation pathway as they volatilize from the water to the air, poses a greater threat to human health than other contaminants examined in this assessment.

This book describes the application of modern information technology to reservoir modeling and well management in shale. While covering Shale Analytics, it focuses on reservoir modeling and production management of shale plays, since conventional reservoir and production modeling techniques do not perform well in this environment. Topics covered include tools for analysis, predictive modeling and optimization of production from shale in the presence of massive multi-cluster, multi-stage hydraulic fractures. Given the fact that the physics of storage and fluid flow in shale are not well-understood and well-defined, Shale Analytics avoids making simplifying assumptions and concentrates on facts (Hard Data - Field Measurements) to reach conclusions. Also discussed are important insights into understanding completion practices and re-frac candidate selection and design. The flexibility and power of the technique is demonstrated in numerous real-world situations.

Shale gas and/or oil play identification is subject to many screening processes for characteristics such as porosity, permeability, and brittleness. Evaluating shale gas and/or oil reservoirs and identifying potential sweet spots (portions of the reservoir rock that have high-quality kerogen content and brittle rock) requires taking into consideration multiple rock, reservoir, and geological parameters that govern production. The early determination of sweet spots for well site selection and fracturing in shale reservoirs is a challenge for many operators. With this limitation in mind, Optimization of Hydraulic Fracture Stages and Sequencing in Unconventional Formations develops an approach to improve the industry’s ability to evaluate shale gas and oil plays and is structured to lead the reader from general shale oil and gas characteristics to detailed sweet-spot classifications. The approach uses a new candidate selection and evaluation algorithm and screening criteria based on key geomechanical, petrophysical, and geochemical parameters and indices to obtain results consistent with existing shale plays and gain insights on the best development strategies going forward. The work introduces new criteria that accurately guide the development process in unconventional reservoirs in addition to reducing uncertainty and cost.

Shale gas reservoirs with multistage hydraulic fractures are commonly characterized by analyzing long-term gas production data, but water flowback data is usually not included in the analysis. However, this work shows there can be benefits to including post-frac water flowback and long-term water production data in well analysis. In addition, field data indicate that only 10-40% of the frac water is recovered after the flowback. This work addresses two main question: Where is the rest of the injected frac fluid that is not recovered and what is the mechanism that is trapping it? And how can the water flowback data be used in estimating effective fracture volume using production data analysis tools? A number of simulation cases were run for single and two phase (gas/water) for modeling flowback and long-term production periods. Various physical assumptions were investigated for the saturations and properties that exist in the fracture/matrix system after hydraulic fracturing. The results of these simulations were compared with analytical solutions and data from actual wells using diagnostic and specialized plots. The results of these comparisons led to certain conclusions and procedures describing possible reservoir conditions after hydraulic fracturing and during production. Past publications have suggested that the lost frac water is trapped in the natural fracture or imbibed into the rock matrix near the fracture face. Natural fracture spacing could be a possible explanation of the lost frac water. These concepts are tested and the challenge of simulating a natural fracture with trapped water without imbibition is solved using a new hybrid relative permeability jail. This concept was tested for the period of flowback, shut-in and production. This work presents the benefits of a new method for combining water flowback and long-term water production data in shale gas analysis. Water production analysis can provide effective fracture volume which was confirmed by the cumulative produced water. This will help when evaluating fracture-stimulation jobs. It also shows the benefits of combining flowback and long-term water production data in the analysis of shale gas wells. In some cases, the time shift on diagnostic plots changes the apparent flow regime identification of early gas production data. This leads to different models of the fracture/matrix system. The presented work shows the importance of collecting and including water flowback data in long-term production data. The electronic version of this dissertation is accessible from http://hdl.handle.net/1969.1/152548