Reservoir Engineering for Unconventional Gas Reservoirs: What Do We Have to Consider?

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. 0

Unconventional gas reservoir evaluation: What do we have to consider?

“…31). Hydraulic fracture modeling (discussed in Clarkson et al, 2011a), yielded a fracture half-length that is consistent with type-curve and linear flow analysis ("RTA-type-curve" and "RTA-straight-line", respectively, in Fig. 31).…”

“…1) for UGRs and address some of the primary reservoir engineering considerations. The reservoir and hydraulic fracture modeling, economic analysis and development planning steps were discussed in Clarkson et al (2011a). In some cases, we will also discuss new techniques that may prove useful for future UGR evaluation.…”

Experimental investigation of the pore structure characteristics of the Garau gas shale formation in the Lurestan Basin, Iran

“…The mineralogy of shales greatly affects the petrophysical and flow characteristics such as porosity, compressibility, fluid saturation and permeability. Mechanical properties, especially brittleness of shales are also functions of mineralogy (Clarkson et al, 2011;Bai et al, 2013) and the proportion of quartzcarbonates-clays could lead to very different mechanical properties. Therefore, the rock mineralogy of shale plays is essential for drilling and completion operations (Bai et al, 2013).…”

Spontaneous imbibition in asymmetric branch-like throat structures in unconventional reservoirs

“…Controlled by capillary force, the fracturing fluid penetrates the matrix through tortuous, complex pore spaces. Rose (2001) and Clarkson et al (2011) claimed that this phenomenon involves a complex interaction among viscosity, surface tension, contact angle, capillary force, gravity, wettability, porosity, and pore structure. Numerical simulation should be performed to identify the key factors and mechanism that influence SI.…”