Integrated Petrophysical Approach to Evaluation of Fracturing in the Eastern Siberia Riphean Deposits

Abstract

In recent years most of the world oil and gas companies focus increasingly greater attention on studying unconventional reservoirs, to which the rocks with secondary porosity can be justly related. The paper presents an integrated interdisciplinary approach, which combines the analysis of overall geological, geophysical, and production information to identify fractured zones and predict their distribution in the formation. The interpretation of formation micro-images, full-wave sonic log, mud log, production log, and core data is combined with well test data for the most effective evaluation of near-wellbore fracturing. Based on core data it was found that vugs predominantly develop in fractures, and the mineral composition of rocks was defined more accurately. The algorithms for determination of mineral composition and porosity based on well log data were proposed. As a result, in correlation with seismic data, the complex approach was developed to fractures identification in well sections and their distribution in the interwell space. Some specific features of hydrocarbons and water distribution in rock were revealed. Main types of fractures (background and feathering) were determined. The method for determination and prediction of general background fractures was presented. It was found that shale volume (Vsh) and bed thickness are the main geological factors, which control the density of background fracturing. It was determined that the intensity of feathering fractures regularly increases towards faults. The qualitative classification of fractures by the level of reliability of their identification was developed, and the comprehensive approach to the estimation of zones with different productivity was proposed. The geological 3D model was generated, which reflects probable zones of fracturing. The paper, for the first time for the Eastern Siberia Riphean deposits, confirms the suggestion that the matrix pores of Riphean deposits in N field are predominantly occupied with residual water, whereas the reserves are concentrated in vugs and fractures. The criteria of reliability of fractured zones identification were drafted.