Crosswell Electromagnetic Tomography in Unconventional Well Geometries
- Michael Wilt (Schlumberger) | Ping Zhang (Schlumberger) | Muhammad Safdar (Schlumberger Middle East SA)
- Document ID
- Society of Petroleum Engineers
- SPE Annual Technical Conference and Exhibition, 30 October-2 November, Denver, Colorado, USA
- Publication Date
- Document Type
- Conference Paper
- 2011. Society of Petroleum Engineers
- 4.1.2 Separation and Treating, 2.2.2 Perforating, 5.1 Reservoir Characterisation, 4.1.5 Processing Equipment, 5.2.1 Phase Behavior and PVT Measurements, 5.6.1 Open hole/cased hole log analysis, 5.4.1 Waterflooding
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Crosswell Electromagnetic (EM) Tomography is a recently developed technology for interrogating the interwell formation resistivity from measurements in boreholes. The tomography data is used for reservoir characterization and for time lapse monitoring of waterflood and EOR processes. Measurements are normally made in vertical wells that encompass the target of interest and collected data are interpreted via computer based inversion.
Modern oil fields often use highly deviated and horizontal wells because they offer improved production and reservoir contact characteristics. These are difficult to use for tomography due to access and sensitivity issues. In addition, the models are in general 3D. In this paper we explore the extension of crosswell EM tomography to non vertical wells. In particular we examine tomography from horizontal wells (HH) and a horizontal-vertical (HV) well combination. Using examples from carbonate oil fields in the middle east we show that the horizontal tomography is an effective method so long as the reservoir has significant thickness compared to the interwell spacing. HV tomography is particularly interesting near horizontal injection wells to track reservoir conformance of the injectate.
Numerical models show that this configuration has a good sensitivity to a variety of structures and processes but that the method is only effective for a limited distance along the horizontal well
Crosswell electromagnetic (EM) tomography was originally developed in the 1990's and later commercialized by Schlumberger in 2005 [1,2].The technique is used for mapping interwell resistivity in snapshot or time lapse modes from which saturation is inferred or calculated. At present, field measurement requires the access to moderately spaced vertical wells, one of which needs to be cased with EM friendly material such as fiberglass or chrome.
The largest obstacle to widespread use of this technology is the issue of well access. Existing wells in operating oilfields are designed for producing and injecting fluids and often have completions that are difficult is not hostile for borehole measurements. The wells often have multiple steel casing strings, tubing and downhole pumps. In addition the casings are perforated and the wells have positive pressure at the surface which requires physical isolation from the downhole pressure. The cost and difficulty of removing completion and setting up pressure equipment for these measurements often stops impending projects before they begin.
Another separate class of access issues is from horizontal or highly deviated wells. Here the wellbore geometry is entirely different and so is the coupling. In addition the tools need to be conveyed by coil tubing or borehole tractors, which adds complexity and cost to the application. After a short look at the application of crosswell EM in vertical wells we will focus our attention on applying this technology in horizontal wells.
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