Low-permeability (tight) oil reservoirs have emerged as a significant source of oil supply in North America. Hydraulic fracturing techniques combined with horizontal well technology have enabled commercial production from oil and gas reservoirs with absolute permeability < 0.1 md, and recently in gas reservoirs with permeability in the nanodarcy range. Techniques for quantitative analysis of ultra-low permeability reservoirs completed with hydraulically-fractured horizontal wells are in their infancy; complications that have slowed development of these techniques include complex reservoir behavior, such as dual porosity effects, multi-layer behavior, multi-phase flow and non-static absolute permeability, and complex flow behavior associated simultaneous flow of multiple hydraulic fractures into horizontal wells. Although analytical models have been and currently are being developed to simulate well performance associated with these complexities, systematic methods for analyzing production for the purpose of quantifying reservoir and hydraulic fracture properties have not been discussed in detail in the literature for tight oil reservoirs.
This paper examines the use of classic rate-transient techniques (flow-regime analysis, type-curve methods and simulation) for analysis of tight oil reservoirs. Single-phase (oil) flow associated with undersaturated black oil reservoirs (above bubble point) is the focus of this work. Simulated cases of multi-fractured horizontal wells completed in single porosity reservoirs, as well as naturally-completed horizontal wells in transient dual porosity reservoirs are analyzed. In all cases, the proposed integrated rate-transient analysis approach provided reasonable estimates of (simulator input) hydraulic fracture and reservoir properties. A field case of a multi-fractured horizontal well completed in a low-permeability area of the Pembina Cardium Field, Western Canada, is also given. Finally, a simplified method for forecasting horizontal wells completed in single and dual porosity media, using inputs derived from flow-regime analysis, is introduced.