Thursday, August 31, 2017

Wirelene /LWD consideratons

Analysis indicates that wireline measurements are advantageous when:

  • Equity decisions are a concern. Because wireline measurements remain the accepted standard, both from technical and legal standpoints , partners may shy away from relying only on LWD measurements when there is a possible equity debate. Some operators view LWD as less desirable in equity decisions because of the need to depth match it with wireline. Depth matching LWD to wireline is often straightforward, but may be complicated when invasion or borehole conditons cause large differences between LWD and wireline logs, or when driller's depth varies nonsystematically with wireline depth. This can happen because of pipe stretch, compression or yo-yoing, or miscounted pipe stands. Absolute depth correction of LWD logs is sometimes done using a gamma ray from the cement bond log when casing is set-usually one to three days after LWD logging. This delay in absolute depth correction does not stall drilling-related decisions based on LWD information. The relative depths of features on the LWD log are used to reference formation tester sample, core and casing points.
  • High temperatures (greater than 320oF (160oC) ) are encountered. Wireline tools typically have a higher temperature rating than LWD tools, which are limited mainly by their use of batteries.
  • Hole size is very large. The current maximum hole size for the CDN tool is 13 3/4 in. 

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