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In the realm of resistivity based Water Saturation equations and introduction to log based Saturation uncertainty analysis

Harish B. Datir, Schlumberger

was presented on Wednesday the 8th of March, 2017.


Estimating the field’s original oil in place (OOIP) for any E&P Company is a crucial part of knowing its worth in terms of money. Among others, the OOIP calculation requires two key inputs from the Petrophysicist; the Total Porosity (PHIT) and the Total Water Saturation (Sw). It also requires understanding of the oil recovery factor (also known as the productivity index), which comes from the reservoir engineer. The uncertainty on computed Sw and PHIT as well as the accuracy of oil recovery factor, can impact the net worth of the field significantly. Hence, it is imperative to perform an accurate petrophysical assessment.

Porosity plays an important role in the estimation of Sw. The uncertainty on the PHIT however depends on the porosity estimation method and the measurements being used. If the density porosity method from logs is used, then porosity uncertainty will depends on how accurate is the formation matrix grain density, the bulk density of the rock, and the formation fluid density. Modern days log measurements provide the most comprehensive set of measurements to evaluate the total porosity accurately and precisely. This enables the Petrophysicist to estimate his porosity with confidence; but when it comes to Saturations, it becomes more elaborated as there is not straight forward answer. By understanding the relationship between PHIT and Sw via the Saturation equations, it will be clearer that the final saturation is not only controlled by porosity but also by the type of water saturation equation is being used and level of detail which is involved. In most cases, the selection of appropriate saturation equation plays a paramount role.

This presentation provides a brief overview on the popular resistivity based water saturation equations, the benefits and difficulties of using them, the selection process. It also shows how the choice of equations can give an erroneous results or drive us to success. In the final stage of the presentation the log based saturation uncertainty analysis is described. The Dual Water equation’s individual inputs and their uncertainty are used to show their specific contribution to the total saturation uncertainty calculation and distribution.

Harish B. Datir, CV

Harish is a Senior Petrophysicist currently working for Schlumberger SIS Data Services, based in Stavanger, Norway. He joined Schlumberger in 2007 as a wireline field engineer and later moved into Petro-Technical Services as a Petrophysicist. He initially worked in Middle East for 4 years and in the North Sea area for the last 6 years. He has a BS degree in applied geology and a Master’s degree in applied geophysics (2007) from the Indian Institute of Technology, Roorkee. He also teaches the NExT designed courses on Formation Evaluation (ELAN), Thin Bed Analysis (TBA) and Acoustics Processing and Interpretation. He has a shared patent on NMR Saturation profiling interpretation technique and one individual patent Memo on nuclear measurement interpretation methodology. His work focuses on providing the petrophysical interpretation for Wireline and D&M measurements and also on developing the integrated petrophysical answer products.