Abstract

Well-site log data interpretation methods are hampered by the slowness of multidimensional inversion techniques, which are accurate but impractical at the well site, and by the inaccuracy of 1D approach, which are error-prone in thinly laminated formations and may overlook productive zones. In this paper, we aim to address this problem with a method enabling accurate near real-time resistivity log data interpretation using fast 2D inversion. The data processing flow is illustrated and tested using a case study for vertical exploration well from the North West Shelf region of offshore Western Australia. The Cretaceous sediments of the deltaic Barrow Group are major hydrocarbon reservoirs in this region. Using this field example we show that our method produces an enhanced formation resistivity model enabling a more accurate near real-time petrophysical analysis that is now achievable only with Geoscience Center computers and expert capabilities. The presented method should be of interest for the industry because it dramatically reduces the time and uncertainties involved in the petrophysical characterization of reservoirs that are crucial for making timely and intelligent decisions on well completions.

Introduction

Due to the very high level of investments required today by the oil industry, there is no doubt that modern E&P processes require an effective and extensive use of innovative technologies and strong efforts for cost optimization. One of the most effective ways to achieve cost optimization is obviously the reduction in time of the operational, interpretation and decision phases in order to anticipate the return of investments. Since well logging technologies play a very important role in numerous phases of the E&P process, today?s operators require faster acquisition procedures as well as faster but still objective and reliable interpretation of well log data to use the results of such interpretation for timely and informed operational decisions. This is true, with different time and operational constraints, both for while-drilling and wireline logging technologies.

To determine the physical properties of the subsurface formations, well log data needs to be interpreted in terms of petrophysical and geological properties throughout a complex process. Even with the latest acquisition technologies, the main steps of this process are:

  1. QC of the acquired data and depth matching;

  2. correction for near-borehole, shoulder-bed, and other environmental effects;

  3. selection of the most adequate petrophysical models and interpretation procedures;

  4. integration of well and reservoir data (logging, core, formation testing, etc.).

With such a complexity, it is evident that a true real-time interpretation of well logs is not effectively possible as long as our standards are to keep an acceptable level of quality and reduction of the uncertainties. For this reason, we prefer to focus on a more feasible near real-time petrophysical analysis (NRTPA) of logging data where efforts are put in operational time reduction in all the steps of the process at the well site; this is specifically important for Steps 1–2.

Since new generation tools are generally designed to acquire a vast amount of data at every logging depth, real-time calibration and processing of the acquired signals is made while logging and with ad hoc plots of specific signals and outputs; the QC of these data is strongly facilitated to the field engineers at the well site.

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