Shale formations have become an attractive target due to their massive estimated hydrocarbon reserve in North America. Due to their ultra-low permeability and their yet to be discovered complexity they are categorized as " unconventional" reservoirs which implies additional considerations and methodology to successfully develop a shale reservoir. Using horizontal drilling and implementing the massive hydraulic fracturing to provide the secondary permeability is the most common practice in shale reservoirs.
The scope of this paper is to illustrate the workflow and methodology to rigorously analyze a horizontal shale gas well with multiple transverse hydraulic fractures. The study well is drilled in Marcellus Shale. Four distinctive scenarios are considered. First scenario considers the well in internal linear transient flow with a larger stimulated reservoir volume (SRV) and drainage area requirement and the implications that arise with this assumption. In the other three scenarios the well is considered to have a transition from internal linear transient flow to internal depletion flow sometime during the well history. Pinning down and identifying the transition time accurately is a key factor in analyzing a shale gas well which affects the reservoir assessment and future well development decisions. In general early transition time implies higher reservoir permeability and smaller effective fracture area compared with a scenario with late transition time. Also due to higher estimated reservoir permeability the flow contribution from outside SRV will be more significant.
Each scenario has been analyzed in detail to demonstrate an easy step by step approach to understand the implication of multiple interpretations on the overall well performance. This approach will help us understand a common problem that is mostly overlooked which is the reservoir contribution outside the SRV - external reservoir volume (XRV). Choosing the correct scenario and identifying the transition time from internal linear transient flow to internal depletion flow is very critical. The effect of key parameters such as: current well flow regime, the time that well has gone to depletion, available drainage area, XRV and SRV size on well performance analysis, reservoir assessment and field development is analyzed in-depth and presented in this paper.