Great Scott! A Homebrewed Recipe for Regional Trend-Based Log Normalization: Various Examples from Rocky Mountain Basins

Abstract

Evaluation of large-scale resource plays often involves thousands of wells, covering a span of hundreds of miles. Proper characterization requires extremely accurate well logs. It is for this reason that log normalization continues to be one of the most important ‘first steps’ in an accurate log evaluation. However, log normalization is often underappreciated, treated as an enigmatic “black box” workflow, or simply avoided altogether. Even less appreciated or understood is a regional trend-based approach like those pioneered by Doveton and Bornemann (1981) and Kate, et al. (2005). In this presentation we address the necessity of accurate log normalization, discuss the various methods available, and present a simple workflow for regional trend-based normalization compatible with standard mapping software Although we present a workflow using Geographix software, the methodology can be used on most software platforms. We begin the analysis similar to other methods by defining our zone of interest, preferably a zone with relatively consistent lithological and petrophysical characteristics over a large area. As an advantage over field-average, or single-well log normalization, this method accounts for regional variations attributed to depositional, and/or compaction trends. Next, cumulative frequency statistics are calculated in the zone of interest for each well and plotted as regional contour maps. Individual well data points that deviate significantly from the norm are then removed from the dataset through visual inspection and analysis of histograms. Using the refined list of datapoints, a set of maps is created using a series of trending algorithms. After selecting the map that best approximates regional trends related to deposition or compaction, the values are sampled back to all of the wells in the project. The values from the regional trend maps are then used as “field values” in a standard one or twopoint field average normalization calculation. Upon completion, the normalized curves are evaluated to determine if they make geologic sense and to reduce variability due to log quality, type, or vintage. This simple approach allows a user to normalize a large set of wells in little time, while accounting for regional geologic variations otherwise ignored by traditional normalization workflows.

AAPG Datapages/Search and Discovery Article #90357 ©2019 AAPG Rocky Mountain Section Meeting, Cheyenne, Wyoming, September 15-18, 2019