ABSTRACT:

This paper presents a new method for determining the formation resistivity structure via sequential interpretation of the Logging While Drilling (LWD) and wireline (WL) resistivity logs. The LWD logs can be used to determine the virgin zone resistivity (Rt), but they do not contain enough information to accurately determine the invaded zone parameters (Rxo / Lxo) primarily because invasion has not occurred at the time of logging. The WL array data contains enough information to accurately determine parameters of both invaded and virgin zones, and inversion gives a direct way of interpreting the WL logs and determining the formation structure. However, the direct application of an unconstrained inversion of the WL data may provide an incorrect (equivalent) solution. To find the true (unique) model from an unlimited number of equivalent solutions, we propose constraining the area of parameter search during the WL data inversion. We do this by utilizing a reference Rt model determined from the LWD data. The following interpretation steps are performed sequentially and lead to a gradual (parameter-by-parameter), stable reconstruction of the formation model:

  • *

    Rt estimation using deep-reading LWD logs inversion

  • *

    Rxo estimation using an Rxo log or shallow-reading WL logs inversion

  • *

    Lxo estimation using array WL logs inversion

To evaluate this method, we tested it on complex benchmark models representing different levels of water saturation in a real case study. To examine the practical validity of the method, we applied it to the LWD Multiple Propagation Resistivity (MPR) and the WL High-Definition Lateral Log (HDLL) array data acquired in a salt-saturated borehole mud environment from an offshore Mediterranean well. The primary objective of the job was to differentiate in the clean sands possible permeable and depleted water levels from deeply invaded and gas bearing ones. This is possible through a comparison of the Rt and Rxo profiles. Application of the method allowed us to reliably determine not only an invasion profile but also a detailed vertical formation resistivity structure. We also demonstrated that the suggested integration of the LWD and WL data provides a way to reduce uncertainty in the formation parameter estimation. This paper presents a complete data processing workflow suitable for practical applications of the method

This content is only available via PDF.
You can access this article if you purchase or spend a download.