The Importance of Integrating Geology and Petrophysical Information Prior to Computer Processing of Log Data
Authors: Bigelow E.L. , Fishburn T.K. , Hinds M. 
Published: December 2007

Misinformation can be as disastrous, technically and financially, as invalid data. Modern log analysis methods implement modern computer technology to facilitate the handling of large amounts of acquired data with speed and mathematical precision. But, computers only do what they are told to do with the controls prescribed, and too often, accuracy of the results is not considered prior to data processing. An abundance of geological evidence is usually available prior to the acquisition of log data or core analysis data. Geology offers unique information that can affect petrophysical parameters, and instruct the log analyst on interpreting logs.

Introduction

The information age is here. But, are we paying a price? Are we accepting log interpretations being carried out in an assembly-line atmosphere that can produce misinformation? The availability of desktop computers and workstations has made it possible to process large volumes of log data in a short time frame. Assuming that the acquired data are of acceptable quality, it is possible to process porosity, saturation, hydrocarbon mobility, and permeability inferences with mathematical precision. At some point, however, log analysis results must be compared to geology — local and regional. Depositional factors are always important to log analysis. Major structural events caused by folding and faulting play an important role in how we should address log analysis. However, few log analyses are accomplished with consideration for geological factors; i.e., the geology is too often compared to the log results after processing is completed.

Carbonates have been known to be processed in error as shaly sands. The examples in this paper demonstrate how misinformation can result even though accurate log processing has occurred. Original computer analyses, subsequently determined to be erroneous, were corrected once geological information was made available. The misspent time, misinformation, and considerable negative criticism could have been avoided if integration of geological and petrophysical knowledge had occurred early on. Awareness of such problems should make those involved seek to compare information from the two disciplines more effectively.

Geology, petrophysics, and computer science should be integrated early into the thought processes of formation evaluation. Terms such as integration and geoscience are used throughout the industry today, but when integration does occur, it is not always done efficiently and effectively. The costs for ineffective handling of log data can be immense. When information is properly integrated, savings in time and money, as well as more competent decision-making, lead to more efficient use of personnel and equipment.

Geological Foresight

Few wells are drilled today without a reasonable comprehension of how numerous geological horizons are made up in the subsurface. True, the predicted nature of the subsurface is rarely 100% accurate, but the stratigraphy and structural nature of the subsurface are usually within tolerable agreement of the predictions.

Oil company geologists and geophysicists usually work together in the exploration and early appraisal stages of a reservoir rock. Following a discovery, logging programs and perhaps some extensive coring are implemented to acquire the best possible information about the subsurface makeup. Where adjustments to the originally predicted real estate are necessary, the borehole data can usually help geophysicists fine-tune the surface seismic data, thereby supplying a very effective and efficient scenario of the reservoir's lateral aspects.

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