Petrophysical Invariance Principle in Adaptive Well Log Interpretation

Abstract

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 reinterpretation; the adaptive technology allows tuning in terms of particular tool metrological characteristics downhole.