The Role of Borehole-Imaging Technologies in Improved Recovery (Examples from the Department of Energy's Class Program)
Authors: Fowler M.L. 
Published: December 2007

Abstract
The cost-effective attributes of borehole surface-imaging technologies (i.e., video, acoustic, and resistivity technologies) make them logical candidates for use in improved recovery projects in both clastic and carbonate reservoirs. Imaging tools provide information about formation fluid content and reservoir heterogeneities at a scale and resolution that was formerly available only through oriented or native-state coring. The U.S. Department of Energy's Class Program is a series of industry cost- shared field-demonstration projects employing detailed reservoir characterization to evaluate and optimally implement improved recovery technologies in reservoirs that contain ample amounts of unrecovered oil but are in danger of being abandoned in the near future. Use of borehole-imaging technologies in Class 1, 2, and 3 projects has been a tremendous aid to reservoir decision making.

Introduction
This paper explores the role that borehole imaging can and does play in the improved exploitation of reservoirs. The focus is on defining the appropriate application of this family of tools for realizing improved oil recovery through more accurate reservoir description. The U.S. Department of Energy's Class Program, in which a wide variety of current and newly developing technologies are being demonstrated in field projects, is a rich source of practical examples from which to draw. A concentrated technology transfer effort is making the critical decision-making processes, application methodologies, and detailed technical and economic results from these projects available to industry.

Boreholes as a Source of Information
After a long history of improved recovery projects blemished with numerous marginally economic to uneconomic attempts, industry as a whole now realizes the importance of adequate reservoir description in improved recovery. Class Program projects place strong emphasis on reservoir description as the key to implementing technically and economically successful improved recovery technologies. Because reservoirs are generally heterogeneous on several different scales ranging from the microscopic scale of pores and individual sediment grains to the gigascopic scale of entire formations, it is extremely important for optimal implementation of improved recovery techniques to have knowledge of vertical and lateral changes in reservoir properties affecting fluid flow at all these scales.
Boreholes are the traditional sampling points at which reservoir descriptive information can be obtained by direct measurement. Information pertaining to all the critical scales is available at the borehole, but the methods for obtaining it vary both in cost and effectiveness. Microscopic scale information on pore structure and rock composition is readily obtained from rock samples through coring. Ditch samples, cores, and wireline logs compared between wells can help establish major or large- scale changes in facies or formational architecture.
There is, however, an important intermediate scale in reservoir description that must be observed and understood to link the large- and small-scale heterogeneities in meaningful ways and allow reservoir fluid flow patterns to be predicted with accuracy. This is the scale at which occur such heterogeneities as thin bed boundaries, stratification types, and other geological features of a similar scale. This is a scale at which information from boreholes has traditionally been difficult and expensive to collect.
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