Pseudo-Focusing Processing of Array Induction Logging Measurements in High-Angle Wells
- Hu Li (Maxwell Dynamics, Inc) | Chao Yuan (PetroChina Research Institute of Petroleum Exploration & Development) | Chaoliu Li (PetroChina Research Institute of Petroleum Exploration & Development) | Xia Li (PetroChina Research Institute of Petroleum Exploration & Development) | Cancan Zhou (PetroChina Research Institute of Petroleum Exploration & Development) | John Zhou (Maxwell Dynamics, Inc)
- Document ID
- Society of Petrophysicists and Well-Log Analysts
- SPWLA 60th Annual Logging Symposium, 15-19 June, The Woodlands, Texas, USA
- Publication Date
- Document Type
- Conference Paper
- 2019. held jointly by the Society of Petrophysicists and Well Log Analysts (SPWLA) and the submitting authors
- 4 in the last 30 days
- 79 since 2007
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In vertical wells, the array induction logging has successfully provided resistivity logs with desirable depths of investigation (DOIs) and resolutions. However, in high angle wells, the “software focusing” processing may fail, due to the severe dip effects. One may observe the horns on the logs near formation boundaries. Moreover, separations of logs with different DOIs may occur in nonpermeable layers. Thus, petrophysicists could be misled in interpreting the so-called resolution matched logs.
In this paper, we present a pseudo, i.e., an inversion-based, focusing approach to process the data measured by an array induction tool in high angle wells. We start from the very original conductivity logs measured by a multi-spacing, multi-frequency tool. First, skin effect correction and borehole effect correction are applied to the data. Then, a set of filters were designed to acquire the logs with matched resolutions. And lastly, a layered-model-based inversion is applied to obtain the “true” resistivity logs. Note that each log, with the specific DOI, will derive an individual “true” resistivity log representing the resistivity inside the corresponding depth.
In addition, the scheme has the following considerations: (1) automatic adjustment of the boundary positions to achieve the optimal fitting; (2) noise containment to minimize the noise amplification during inversion; (3) analytical expression for the sensitivity function, or the Jacobean matrix, in a general layered medium to accelerate the inversion; (4) automatic consistency analysis of the results inverted from logs with different DOI.
Both synthetic and field data sets are processed to showcase the implementation of the developed method. The pseudo-focusing processing is proven to be stable, effective and efficient. In vertical wells, the results from the proposed approach are compatible with those from the “software focusing” processing. While, in high angle wells, the dip effects are eliminated to a substantial degree. The pseudo-focused resistivity logs, which have matched resolution, characterize the formation radial resistivity profile convincingly, may greatly help the formation evaluation and log interpretation in high-angle wells.
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