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Abstract
The reservoir engineer involved in the development of unconventional gas reservoirs (UGRs) is required to integrate a vast amount of data from disparate sources, and to be familiar with the data collection and assessment. There has been a rapid evolution of technology used to characterize UGR reservoir and hydraulic fracture properties, and there currently are few standardized procedures to be used as guidance. Therefore, more than ever, the reservoir engineer is required to question data sources and have an intimate knowledge of evaluation procedures.

We propose a workflow for the optimization of UGR field development to guide discussion of the reservoir engineer’s role in the process. Critical issues related to reservoir sample and log analysis, rate-transient and production data analysis, hydraulic and reservoir modeling and economic analysis are raised. Further, we have provided illustrations of each step of the workflow using tight gas examples. Our intent is to provide some guidance for best practices. In addition to reviewing
existing methods for reservoir characterization, we introduce new methods for measuring pore size distribution (small-angle neutron scattering), evaluating core-scale heterogeneity, log-core calibration, evaluating core/log data trends to assist with scale-up of core data, and modeling flow-back of reservoir fluids immediately after well stimulation. Our focus in this manuscript is on tight and shale gas reservoirs; reservoir characterization methods for coalbed methane reservoirs have recently been discussed.

Introduction
The primary functions of a reservoir engineer, according to Dake (1978) are "estimation of hydrocarbons in place, the calculation of a recovery factor and the attachment of a time scale to the recovery". For modern reservoir engineers, this process will include estimating fluids-in-place and forecasting fluid production for play and prospect analysis, asset valuation, resource and reserves estimation, and field development planning. For conventional reservoirs, there are "tried and true" methods for performing these duties that are an outcome of relatively well understood fluid storage and transport mechanisms for these reservoir types. Many techniques for quantifying key reservoir properties controlling storage and flow, calculating hydrocarbons in place, establishing recovery and forecasting production have a long history of development and refinement. The reality for unconventional gas reservoirs (UGRs), including low-permeability (tight gas), coalbed methane (CBM) and shale gas reservoirs, is that fluid storage and transport mechanisms are poorly understood, and we are at an early stage for some reservoir types (ex. shale gas) in the development of such methods. Further, it is not just necessary to characterize the reservoir in unconventional plays but also the induced hydraulic fracture(s) or fracture network, that have a large impact on well performance, yet methods for evaluating hydraulic fracture properties are also in their infancy. Indeed there are new methods for unconventional reservoir and hydraulic fracture analysis (ex. microseismic monitoring and analysis) that are considered critical to the evaluation process that have only routinely been used for oilfield applications in the past decade; it is the job of the UGR engineer to keep on top of new developments, understand the uncertainties and the consequent impact on their evaluations.