Appraising Unconventional Resource Plays: Separating Reservoir Quality from Completion Effectiveness

Abstract

Appraisal wells in unconventional, very low permeability, resource plays require large hydraulic fracture treatments to assess economic viability. In many cases, drainage area and hydrocarbon recovery are defined by the areal extent and effectiveness of the hydraulic fracture treatment. To increase the drainage area and recovery per well, multiple hydraulic fracture treatments in horizontal and vertical wells are now common, resulting in more complex and expensive completions. Therefore, appraising the completion and hydraulic fracture treatment are just as important as appraising the reservoir. Unlike conventional reservoirs, the complexity and heterogeneity of unconventional resources can make reliable reservoir characterization difficult, which can result in significant uncertainty when evaluating appraisal well performance. Therefore, applying the appropriate technologies for unconventional reservoirs and a holistic approach are essential to properly separate reservoir quality from completion effectiveness. This paper details technologies and workflows that are essential to the reliable appraisal of unconventional resources, with an emphasis on appraising resources outside of North America. Due to the high cost of appraisal wells in most environments outside North America, operators must assess the viability of unconventional resources using as few wells as possible. The North American model of assessing unconventional reservoirs by drilling and completing a large number of wells may not be economically feasible in areas with insufficient hydraulic fracturing, drilling, and completion infrastructure.Due to the variability of both hydraulic fracture growth and reservoir characteristics in unconventional reservoirs, properly assessing new plays and subsequently optimizing fracture treatments and completions has historically been a -trial and error‖ process requiring a large number of wells and significant capital risk. However, efficient evaluation of stimulation treatments and completions is now possible by combining microseismic mapping and other hydraulic fracture diagnostics with advanced logs, specialized core tests, 3D seismic, and newly developed -unconventional‖ hydraulic fracture models. This holistic approach reduces the number of wells required to assess the economic viability of unconventional resources and reliably separates reservoir quality from completion effectiveness. The application of these unconventional-reservoir-specific technologies, newly developed hydraulic fracture models, and specialized workflows are illustrated using examples from North America.

Classification and characteristics of tight oil plays

“…Low clay content and high contents of quartz, feldspar, dolomite, and other brittle minerals are favorable for the implementation of hydraulic fracturing and other reservoir stimulation treatments (Cipolla et al 2012). In abovesource, below-source, between-source, and beside-source plays, the hydrocarbon mainly accumulates in the tight formations that are adjacent to reservoirs.…”

Using technology to evaluate and optimize unconventional resource development

“…Organic shale reservoirs are all fine-grained, argillaceous sediment containing mud, clay, and mudstone, as well as organic material 12) . Because of their fine-grained nature, all organic shale reser voirs are complex, extremely lowpermeability formations.…”

“…Shales tend to be highly variable(laminated)from a mineralogical standpoint within the vertical pay section. 1) , 2) , 12) Variations in mineralogy and other reservoir properties create complexity in terms of reservoir quality and completion quality, and must be quantified and understood in order to correctly assess productivity potential.…”

Visualization of drained rock volume (DRV) in hydraulically fractured reservoirs with and without natural fractures using complex analysis methods (CAMs)

“…Likewise, conventional reservoirs produced via hydraulically fractured wells in the presence of highly conductive fractures and non-conductive natural fractures will affect the flow region near the hydraulic fractures (Doe et al 2013). Consequently, the most accurate flow simulation and production forecasting models must strive to account for the impact of natural fractures, based on their orientations, distributions, connectivity, strengths and interactions with the hydraulic fractures (Olson 2008;Cipolla et al 2011;Kang et al 2011).…”