The oil industry has traditionally concentrated on exploration and production of conventional clastic and carbonate hydrocarbon plays. More recently, though, fewer new conventional plays are being discovered, causing the industry to shift its attention to unconventional plays.
In addition to ‘shale’ plays, the existence of other types of unconventional plays such as fractured igneous reservoirs has been known for some time. Historically, unconventional plays have been overlooked by the industry because conventional petrophysical models cannot accurately quantify mineralogy and hydrocarbons in place. Very few analysis models have been developed, and a custom interpretation model is often required for individual plays.
Consequently, the oilfield services industry has developed new technologies for evaluating these formations. Pulsed neutron elemental spectroscopy services can accurately quantify complex multi-mineral lithologies. In-situ lithology-independent measurements of porosity, hydrocarbon saturation and hydrocarbon typing can be achieved with advanced nuclear magnetic resonance services. When the technologies are integrated, traditionally challenging formations can be accurately appraised.
The paper presents a case study where wireline pulsed neutron mineralogy, nuclear magnetic resonance, borehole imaging and formation pressure tester measurements are applied to appraise an unconventional igneous-fractured basement reservoir. A general model and workflow are proposed that enable accurate quantifying of mineralogy, water saturation and producibility in other fractured igneous reservoirs.