In order to more accurately characterize reservoir and hydraulic fracture properties from well performance, a workflow has been developed that effectively integrates variable quality data from a variety of sources. This workflow applies analytical techniques designed specifically for shale gas wells followed by as-needed numerical modeling. The analytical techniques can be applied to multiple wells through time to: a) identify groupings of like-performing wells, b) detect wells with anomalous behaviors, c) develop hypotheses about production mechanisms, and d) choose specific wells for more detailed analysis and numerical modeling. Numerical modeling provides the functionality needed for complex mechanism forensics, performance forecasting, and completion optimization studies. Conventional numerical models typically use finite-difference grids, but these are neither sufficiently complex nor sufficiently flexible for shale gas reservoirs. For this reason, a finite-element modeling technology has been applied that places a large number of closely-spaced nodes near hydraulic fractures, "where all the action takes place" in the early life of a well. The finite-element technique also allows complex fracture geometries to be modeled. This workflow, incorporating analytical and numerical solutions, has been applied to multiple shale gas projects, including industry consortia in the Haynesville (US) and Montney (Canada) shales and individual operator projects in the Woodford (US), Horn River (Canada), and Marcellus (US) shales. Through the application of these techniques, fracture and reservoir properties have been characterized and uncertainty associated with forecasted well performance has been reduced. This work has profound implications for quantifying gas reserves, understanding those factors responsible for variations in well performance, and for optimizing well spacing, lateral lengths, and completion techniques.

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The use of multi-stage fractured horizontal wells has made production from shale gas plays feasible. The production history from these wells is characterized by long transient linear transient flow. The key reservoir (nature) and completion (nurture) properties that impact flow behavior of the well are permeability, Original Hydrocarbon in Place (OHIP), number of hydraulic fractures, fracture area and fracture spacing. Understanding the interrelationship between these parameters is critical for optimal development of shale gas resource plays. The proposed shale gas workflow uses a hybrid analytical model. An analytics based diagnostic process analyzes well performance history and a numerical model validates the feasible history match models for representative forecasts. The model results allow the user to capture the range of uncertainty in estimating individual reservoir or completion properties, such as permeability, fracture area, fracture spacing, etc. The diagnostic process provides the relationship between key factors dictating well performance such as OHIP, effective fracture area, effective reservoir permeability, effective fracture spacing and well spacing. In this paper, wells from the Marcellus play, in Pennsylvania, USA are evaluated using the proposed shale gas workflow. Surveillance is an integral part of this workflow. The paper shows how surveillance can be used for resource management and exception management. Along with data mining, the workflow accelerates the learning curve to evaluate the effectiveness of current field practices. The results help with understanding the effectiveness of proppant pumped, the potential number of contributing clusters and production issues. Continued surveillance reduces the uncertainty surrounding all parameters. This knowledge base can then be used to optimize the asset development strategy, maximizing the return on investment (ROI).

Transient linear flow diagnostic plots in shale gas wells often exhibit a positive y-intercept and may mask the early transient linear flow regimes because of non-reservoir pressure drops. Increased completion resistance reduces the peak production rate early in the life of a well impacting NPV. The shale gas industry is very early in the research required to distinguish the individual contributions of completion resistance, e.g. poor fracture conductivity, near-perforation damage or choke skin, and fracture face damage skin. Many of these phenomena can be diagnosed in production wells using unique shape(s) from various diagnostic plots allowing for analysis of completion effectiveness.Mechanistic reservoir simulations were used to generate diagnostic plot signatures for low conductivity fractures, choke skin, and near fracture face damage. Subsequently, the corresponding signatures were compared with a large database of shale gas wells in numerous plays across North America to aid in the fingerprinting of these non-reservoir pressure losses. Only low fracture conductivity, not choke skin, can have a quarter slope. Near fracture face damage results in two distinguishable linear trends, one of the damaged region and the other for the matrix.Completion skin diagnosis is a way of evaluating fracture efficiency by identifying the root causes of the non-reservoir pressure losses so as to mitigate them in the future. The following presents a catalogue of signatures that enables greater diagnostic capabilities to classify non-reservoir pressure losses. The study is the first comprehensive cause-by-cause look at completion damages with an emphasis on identification and diagnosis in shale gas wells.

Underground coal gasification (UCG), in the recent years, have gathered a significant amount of interest from the researchers because of its advantages over conventional mining and utilization techniques. It is one of the most promising and innovative technology where coal is gasified in-situ by injection of a suitable oxidant for the production of synthetic gas. The simultaneous occurrence of several phenomena such as complex flow patterns, chemical reactions, water influx, thermo-mechanical failure of the coal seam etc. make the mathematical modeling of the entire UCG process very abstruse and computationally challenging. The reaction between the oxidant and the coal in the deep underground seams leads to the formation of combustible gas and subsequently results in a cavity. As the gasification proceeds the cavity grows three dimensionally in a non-linear fashion. The cavity size strongly depends on several parameters like position and orientation of the inlet nozzle, coal properties etc. A comprehensive three-dimensional numerical study is conducted to understand the hydrodynamics within a given cavity size which would give us a relatively quick but reliable insights into the process. Five different cavity sizes are considered inside which the complete turbulent transport is simulated. Apart from the usual vertical and horizontal injection, the effect of inclined injection on the hydrodynamics is also reported here for the first time.