Integrated Approaches to Determining Net Pay: Caveats & Lessons Learned

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Net pay is the formation thickness within the hydrocarbon column that can be produced economically. The most common methods for determining net pay include wireline log cut-offs e.g. gamma ray (sand vs shale percentage), resistivity (hydrocarbon vs water saturation) and porosity (rock vs pore volume).

This presentation details case histories from around the world that highlight various challenges with relying on many of these methodologies. Overly simplistic assumptions of wireline log response, and poor understanding of fundamental rock and fluid properties in the formation, have caused misinterpretation of pay in many formations. Examples include incorrect v-shale cut-offs due to shale clasts, incorrect density porosity calculations caused by extreme mineral densities, incorrect neutron porosity cut-offs due to microporous reservoirs, and misinterpreted fluid compositions (on resistivity logs) due to conductive minerals in the formation. Potential errors in quantifying reservoir properties may occur even when core data are plentiful. This is commonly due to core plug sampling bias, either from poor core and/or core plug recovery or due to human sampling bias; both biases result in over or under representation of particular rock types. Often, production mechanism and net pay interpretation are not considered together. Pay on primary production, may not equate to pay on waterflood, if the flooded formation is discontinuous or sweep efficiency is low. In addition, production or injection zone tests (eg PLT), are rarely correlated to rock types in a formation, thus leading to mismatch between actual and interpreted pay zones. Net pay determination is improved markedly when petrophysical properties are linked to field-specific production mechanisms.


Your Instructor


John Kaldi, PhD, PESA
John Kaldi, PhD, PESA

John Kaldi is a Professor of Petroleum Geology and Engineering at the Australian School of Petroleum and Energy Resources, University of Adelaide, and holds the South Australia State Chair in Carbon Capture & Storage (CCS). He is also an Adjunct Professor at Institut Teknologi Bandung (ITB), Indonesia, and a Visiting Professor at Universiti Teknologi Petronas (UTP) in Malaysia.

John received his Bachelors and Master’s degrees in geology from Queens College, City University of New York, and a PhD in Geology from Cambridge University in the UK. His career includes 18 years in the Petroleum Industry in both technical and managerial roles with Shell, Arco & Vico.

John served as Distinguished Lecturer for various professional organisations, including SPE, American Association of Petroleum Geologists (AAPG), the Indonesian Petroleum Association (IPA) and the Petroleum Exploration Association of Australia (PESA). He has been the author and presenter of over 150 journal articles and technical conference papers.



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