The Dangers of Not Integrating Wireline Specialty Services with Other Information
Authors: Bigelow E.L. 
Published: October 2008

Modern computer log analysis methods integrate several types of log measurements to arrive at porosity, saturation, lithology, producibility indices, etc. Yet, specialty services such as dipmeter. wireline testing, and others are considered by too many to require a stand-alone interpretation only, Specialty services also need to be compared to several other types of information if the user is to fully benefit from the acquired data. This article demonstrates how easily specialty measurements. by themselves. can be badly misinterpreted. Such data are often condemned as erroneous simply because they have not been compared to other information that often crystallizes the real meaning of the data.

Introduction

Today's economics demand accurate analysis of all acquired information [hat is used to evaluate reservoirs. Effective and efficient use of specially data often requires more integration than the routinely acquired well log suites. Computer log analysis technology has evolved to the point that data from several wireline services can be routinely integrated into se!ective interpretation models to derive petrophysical and geological answers that describe and characterize subsurface reservoirs.

Wireline specialty services are too often left to their own basic interprelative parameters, which can unfortunately be completely misleading because other available data have not been used to obtain a clearer understanding of the specialty measurements. Wireline formation tests and computed dip data are two expensive services often abused for the previously mentioned reason.

Examples of dipmeter results and wireline formation tests that were originally interpreted as erroneous are shown to be accurate measurements of particular well conditions. Other information resolved the questionable data and, in fact, showed formation pressure and dip measurements to perform as they should in those specified circumstances. Both are striking examples of poor practices, and the importance of including other evidence into any interpretation. Eventually, other information was integrated into the dipmeter and wireline test data interpretation, which proved the validity of the original measurements.

Confronting the Perceived Problems

The subject well for this discussion was drilled with 16.3 lb/gal oil-based mud. The following wireline services were run: dual phase induction, compensated formation density, compensated neutron, gamma ray, multiarray acoustic. six-arm dipmeter. and formation multitester. After completing the well logging operation, the accuracy of acquired wireline pressure test data was almost immediately questioned. Several clients considered the data erroneous. Following The post processing of the acquired dipmeter data, the computed dip results were also declared inadequate, inaccurate, and/or uninterpretable.

Conventional log analysis from a combination of dual phase induction, density. neutron, gamma ray, and multi array acoustic instruments was also severely criticized for either inaccuracy or differences in answers from at least three quarters. Porosity and lithology solutions were acceptable, but the saturation values varied considerably. Three different sources of interpretation demonstrated three widely differing saturation ranges (e.g., 52%, 66%, and 83% at one depth level). The cause for the differing saturations was quickly found to be the connate water resistivity values used in the different analyses (i.e., R, r values of 0.10,0.16, and 0.25 ohm-m).