A new methodology for grouping and averaging capillary pressure curves for reservoir models

Primary drainage capillary pressure data are usually correlatable with a 3D predictable property of grid cells.Accordingly,rock typing is normally performed based on an established correlation.Primary drainage as well as corresponding imbibition and/or secondary drainage capillary pressure curves are averaged to establish a saturation table for each rock type region in reservoir modeling.This study in-vestigates the reliability of this industry-accepted methodology,and has two main contributions.First,we show that if different types of capillary pressures are plotted against water saturation,comparing them might be highly misleading.We demonstrate that although primary drainage capillary pressure data may be plotted against water saturation,the imbibition and secondary drainage capillary pressure data should be plotted against imbibed water saturation.This would enable reservoir engineers to check whether rocks with similar primary drainage capillary pressures do or do not have similar imbibition/secondary drainage counterparts.Using this technique,rock quality can be also deduced from imbibition and secondary drainage capillary pressure curves.We use capillary pressure data measured on limestone and sandstone samples from the Asmari Formation in three Iranian oilfields to evaluate our technique.The second contribution of this study is the proposal of a new methodology for preparing capillary pressure curves for reservoir models.In our methodology,a grid cell can represent more than one rock type region,each specific to a saturation function.As a part of this methodology,we present new physically meaningful equations for averaging primary drainage,imbibition,and secondary drainage capillary pressure curves.

Analysis of the bounded and unbounded forms of USBM wettability index

Understanding wettability is important in many processes where porous media and fluids are in contact.The U.S.Bureau of Mines(USBM)is one of the industry standard techniques for measuring wettability.This index is calculated as USBM=lg(A_(1)/A_(2)),where A_(1) and A_(2) are the areas under capillary pressure curves of oil-drive and water-drive processes,respectively.Usually,the USBM is mistakenly assumed to vary over the range of-1 to 1 and compared with other indices.In this study we indicate that the lower and upper bounds of this index are not fully known in practice.As a result,comparison between USBM and other indices may cause erroneous interpretations due to dissimilar ranges of variation.In addition,even during examining the USBM of a sample it may not be possible to accurately interpret its wettability.We highlight the bounded form of the USBM index(denoted as USBM^(*)=A_(1)-A_(2)/A_(1)+A_(2)),which varies over the range of -1 to 1,and suggest that it should replace the traditional form of USBM index.Twenty limestone coreplugs were collected from Asmari and Fahlian formations in two Iranian fields.These samples were used for performing primary imbibition relative permeability measurements,as well as primary imbibition and secondary drainage capillary pressure tests.These experiments are used to show the differences between USBM and USBM^(*)in comparative studies and compare them against other indices of Amott-Harvey,Lak and modified Lak.

A new framework for selection of representative samples for special core analysis

Special core analysis(SCAL)measurements play a noteworthy role in reservoir engineering.Due to the time-consuming and costly character of these measurements,routine core analysis(RCAL)data should be inspected thoroughly to select a representative subset of samples for SCAL.There are no comprehensive guidelines on how representative samples should be selected.In this study,a new framework is presented for selection of representative samples for SCAL.The foundation of this framework is using methods of PSRTI,FZI*(FZI-star)and TEM-function for the early estimation of petrophysical static,dynamic,and pseudo-static rock types at RCAL stage.The global hydraulic element(GHE)approach is benefitted and a FZI*-based GHE method(i.e.,GHE*)is presented for partitioning data.The framework takes into consideration different laboratory,reservoir engineering,geological,petrophysical and statistical factors.A carbonate reservoir case is presented to support our methodology.We also show that the current forms of Lorenz and Stratigraphic Modified Lorenz Plots in reservoir engineering are not appropriate,and present new forms of them.

Investigating dynamic rock quality in two-phase flow systems using TEM-function: A comparative study of different rock typing indices

Constructing a reservoir simulation model requires an accurate definition of saturation functions,including capillary pressure and relative permeability data.Usually,these saturation functions are available only for a limited number of samples.Assigning saturation functions to the simulation model requires finding a clear relationship between them and a 3D predictable property of grid cells.Different indices are usually evaluated to describe such a relationship.It was recently shown that each petrophysical dynamic rock type should form similar True Effective Mobility(TEM)curves.In this study,TEMfunction was used to evaluate the reliability and performance of different rock typing indices in defining dynamic rock types.FZI,FZIM,MFZI,and FZI*(FZI-star)indices were considered and tested on a collection of laboratory-derived core-flooding data from an Iranian carbonate reservoir.Results showed that FZI-star had a better performance than FZI,MFZI,and FZIM.