The Role of Open Hole Memory Logging and Wireless Conveyance Systems in the Evaluation of Horizontal Wells
- Peter A.S. Elkington (Reeves Technologies Ltd.)
- Document ID
- Society of Petroleum Engineers
- SPE/CIM International Conference on Horizontal Well Technology, 6-8 November, Calgary, Alberta, Canada
- Publication Date
- Document Type
- Conference Paper
- 2000. SPE/PS-CIM International Conference on Horizontal Well Technology
- 1.6 Drilling Operations, 4.1.6 Compressors, Engines and Turbines, 1.10.1 Drill string components and drilling tools (tubulars, jars, subs, stabilisers, reamers, etc), 1.7.5 Well Control, 1.12.2 Logging While Drilling, 1.12.1 Measurement While Drilling, 3 Production and Well Operations, 1.10 Drilling Equipment, 1.6.10 Running and Setting Casing, 5.6.1 Open hole/cased hole log analysis
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Open hole formation evaluation logs are not run where the perceived benefits are marginal. In many horizontal wells, the benefits are not fully assessed because cost and/or access difficulties override other considerations. In these cases, sub-seismic lateral variations in reservoir properties can only be inferred - they are rarely measured. Small diameter battery-powered logging tools operating without a wireline have collected high quality data in a broad range of high angle situations. Wireless conveyance techniques are faster and safer than wireline pipe conveyed logging, and have cost, access and data quality benefits over logging while drilling (LWD). Wireless tools have been conveyed in and on drill pipe, on coiled tubing without an electric line, and as part of a modified casing string. The tools can be deployed safely in underbalanced wells.
High angle, horizontal and extended reach wells are challenging environments for the acquisition and interpretation of formation evaluation data.1 Pipe conveyed logging (PCL) using conventional wireline tools, and logging while drilling (LWD) using instrumentation behind the bit, are the established acquisition methods. In a minority of cases, wireline tools are conveyed on coiled tubing (CT).
PCL data are acquired after drilling. The tools and associated wireline (which carries power and data) are pushed by the drill string. The string must include a side-entry sub through which the wireline can pass and be pumped down to the tools where an electrical connection is made using a wet-connect system. The risk of damage to the wireline means the side-entry sub is not allowed to pass into open hole. If the interval to be logged is greater than the depth of the casing shoe, the side-entry sub must be re-positioned and the wet-connect re-established before logging can resume.
Above the side-entry sub the wireline is outside the drill pipe, so it may need to be cut if pipe rams are used to control the well during logging. Any pipe rotation risks loss of electrical connection and damage to the wireline.
Log depth is determined by measuring the position of the wireline in the well; it is reliable only if the wireline spool speed matches the pipe speed. The care needed to achieve good depth control, and the time needed to achieve an electrical connection, particularly where multiple latches are required, make wireline PCL a complex and time consuming operation.
LWD data are acquired during drilling. Batteries or turbines supply power, and data are memorized within the tool string. A sub-set of the recorded data is transmitted back to surface using mud pulse telemetry, a feature that allows formation evaluation data to be used in the steering of wells with respect to anticipated targets. Mud pulse telemetry may not work in underbalanced situations.
Data are sampled at regular time increments then merged with pipe position and speed data recorded to produce logs with respect to depth. The depth interval between samples is therefore not regular, and depends on the rate of penetration of the drill string.
In normal operation the LWD string is rotating during acquisition. Azimuthal measurements take advantage of this, but variations in tool standoff may compromise the quality of sidewall measurements (principally the density). Tools are occasionally run in sliding mode after drilling.
LWD measurements rely on the same physical principles as those made on wireline, but curves may differ in name, value and character because of differences in implementation. When both data sets exist in the same field, considerable effort may be required to reconcile them.2,3
In many respects, CT is an ideal deployment vehicle for logging tools. Speed and depth control are good, power and data are transmitted via a pre-installed electric line, and deployment is possible in underbalanced wells. Set against these are high deployment costs and limited horizontal reach.4
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