Standard Workflows to Integrate Borehole Images with other Openhole Logs for Reservoir Characterization

Abstract

Proposal Borehole images provide high-resolution information on the layering, texture, and dip of rocks and sediments and permit core-like description of subsurface reservoirs. Conventional openhole wireline logs. e.g., gamma, SP, resistivity, and porosity measured by nuclear, sonic, and NMR sensors provide complementary bulk petrophysical properties of formations. Thus, a proper integration of the electrical images with the conventional logs could provide an extremely powerful tool for reservoir characterization. However, image logs still remain a mystery for many E&P Operators. They are underutilized - largely because the workflows to integrate them with the conventional logs and other well or field data are not yet commonplace. This paper proposes standard computer-aided work-flows for the geological and petrophysical evaluation of the siliciclastic and carbonate reservoirs. The workflows involve integrating high resolution images with conventional open hole logs. Specially built software assists the user to identify lithofacies, depositional facies, and high frequency stratigraphic changes on the high resolution images. Sedimentary cycles and bed-sets and packages are then interpreted and combined with the other logs to generate electro-facies. Reservoir fluid volumes and estimation of netto- gross pay are included in the standard answer product. Results of the integration are then combined with the other well and field data to perform sequence stratigraphic analysis. The paper includes case histories of successful applications from the Permian and the Fort Worth Basins and from other basins in the US and Mexico. We demonstrate that the proposed integrated workflows can significantly enhance accuracy in reserves estimation and reservoir fluid flow modeling. These workflows can be applied to multi-well reservoir characterization by tying the key stratal surfaces and sedimentary features from image logs to seismic. Using image logs ultimately reduces uncertainties of the interpretation of external geometry, internal architecture, and lateral variations in oil and gas reservoirs. Introduction Although, a greater number of petrophysicists and geologists now routinely use borehole image logs** in their reservoir characterization programs, they do not appear to follow a set workflow to achieve a standard interpretation of the reservoir characteristics from borehole images. In part, lack of a consistent workflow is due to the fact that many users of image logs continue to view them only as pretty pictures of the formations exposed on the borehole walls. Partly, it is also due to the difficulties associated with up-scaling the very high resolution image logs when integrating them with other open hole logs. Finally, a part of the reason for lack of effective workflows may be lack of awareness and training with respect to the various image interpretation techniques that can reveal specific reservoir characteristics. Objectives of this paper are:to identify a standard set of reservoir characterization goals in E&P and review the role of image interpretation in achieving these goalsto recommend an interpretation workflow based on image processing software techniques to integrate borehole images and all the other open hole logs. It is hoped that this standardization would help maximize the value of borehole image logs and benefit petrophysicists and geoscientists in their global E&P efforts. ** Note - The terms image logs and imaging as used in this paper refer to the wireline electrical or acoustic borehole images acquired in either water- or oil based mud wells.