Отправлено: 13.04.11 12:30. Заголовок: D.Kozhevnikov and K.Kovalenko

135977-MS
DOI What's this? 10.2118/135977-MS
Title

Petrophysical Invariance Principle in Adaptive Well Log Interpretation
Authors

D.Kozhevnikov and K.Kovalenko, Gubkin U
Source

SPE Russian Oil and Gas Conference and Exhibition, 26-28 October 2010, Moscow, Russia
Copyright

2010. Society of Petroleum Engineers
Language English
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Abstract
The adaptive interpretation technique developed which allows of significantly reducing the number of error sources and improving accuracy, reliability and informativmess of the well logging results.

The existing conventional interpretation technology of the well logging data in comparison with adaptive one has a lot of uncertainties because of the information deficit about petrophysical and petrochemical characteristics of the mineral components and other factors affecting measurements.

The well logging data interpretation is basically focused on definition of porosity in studying of oil and gas reservoirs. But for the complex reservoirs porosity has appeared to be a misinformation parameter: the reservoir rock with high porosity may fail to possess effective porosity that is it may not be a reservoir. It is necessary to consider a corresponding petrophysical model to substantiate effective (and dynamic) porosity as a direct interpretative parameter of the well logs.

It is possible to introduce an alternative adaptive interpretation for the effective porosity evaluation. The adaptive interpretation is based on the petrophysical invariance of the reservoir and is using the petrophysical invariant as the main interpretation parameter.

The way how the petrophysical invariant can be calculated directly from the well logging data established. It is shown that different well logs can be used for the effective porosity evaluation.

The adaptive technology advantages include: effective (dynamic) porosity can be calculated for the complex polymineral reservoirs in absolute units without “reference beds”; the technology provides adaptive tuning under lithological and petrochemical conditions of the particular reservoir in situ, including the wellbore construction influence; in contrast to the conventional interpretation the adaptive technology does not require any tools standardization; it can be used for the old data re-interpretation; the adaptive technology allows tuning in terms of particular tool metrological characteristics downhole.

Introduction
Effective porosity is defined as a difference between total porosity and amount of bound or residual water:
цef = цt (1 – Swr) (1)
Effective porosity reflects formation capacity which is accessible for free water movement.

For hydrocarbon saturated formations description of dynamic porosity is used. Dynamic porosity is the difference between total porosity and unmovable water and hydrocarbons:
цdyn = цt (1 – Swr– Sor) (2)

According to (1) it is important to have an analytical model of dependence between total porosity and residual water saturation. Some authors propose that product цt Swr = const (Coates et al., 1974) but this is not the case for clayey formations.

Both these dependences were studied and an important petrophysical property of the granular reservoirs was established. This property is called “petrophysical invariance” and establishes parameter called “petrophysical invariant”. It was established that for granular reservoirs the ratio of effective porosity and maximum effective porosity for particular reservoir is an invariant:
Ш = цef / цef max (3)

It was also established that for hydrocarbon saturated reservoirs the ratio derived by the similar way represents the same parameter:
Ш = цdyn / цdyn max (4)

These conclusions have great practical importance, as petrophysical invariant can be calculated directly from well logging data. Association of reservoir petrophysical models with well logs petrophysical models allows proving petrophysical invariant as the direct interpretative parameter.
Number of Pages 16