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Continuous Microfacies Analysis in Clastic Environments Utilizing Pseudo Grain Size Distribution from Electrical Borehole Images
- Publisher: European Association of Geoscientists & Engineers
- Source: Conference Proceedings, Second EAGE Borehole Geology Workshop, Oct 2017, Volume 2017, p.1 - 15
Abstract
Summary
Sediment particle size and its distribution are fundamental attributes of sedimentary deposits that provide key information for reservoir quality evaluation. Traditional grain-size analysis can only be obtained from laboratory testing on rock samples from cores. In the absence of core or suitable cutting information, borehole images and nuclear magnetic resonance (NMR) logs are basic input data to estimate grain size. Recently several approaches were proposed for grain-size analysis from NMR for depositional environment studies and expandable sand screen design. In this paper, we propose a new approach for the continuous microfacies analysis from pseudo grain-size distribution of borehole resistivity images.
The true size of particles is very difficult to be measured directly from borehole resistivity image, especially when the particle size is less than the tool button size; additionally, correction factors are different for conductive and resistive particles depending on the resistivity contrast. Based on the high resolution resistivity image, we assume that the resistivity of multiple button measurements represents the particle size relatively, similar to the principle of analyzing textural changes within clastic environments using electrical borehole images. The cumulative probability of each resistivity curve represents a similar statistic to that of grain size in laboratory experiments and indicates the different hydrodynamic conditions. In certain geological settings, the continuous microfacies analysis can be achieved from the cumulative frequency curve shape.
One case study were performed to verify this new approach in Fan delta depositional environments. The analysis results are consistent with drilling core data and provide the detailed microfacies information for sand unit correlation analysis in multiple wells. We find this method is robust in the fluvial system and conglomerate-related depositional environments, and but it is very challenging to distinguish the mouth bar and channel fill in a river-dominated delta ( Yang et al 2016 ).
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