Monday, August 28, 2017

LWD/ Wireline Comparisons

In the several years since LWD technology became available, the industry has found five main applications for these tools:

  • Insurance logging, in case the well is lost, can't be logged with wireline tools or will yield poor-quality wireline logs.
  • Logging before invasion, which may reveal hydrocarbon zones that might be missed by wireline time. In some high permeability formations, borehole fluid displaces hydrocarbon from the near wellbore rock, making the well look like a dry hole by the time of wireline logging. This effect may be more common in horizontal than vertical wells because the drainhole is exposed to full hydrostatic mud pressure for the long period required to drill the lateral section.
  • Geosteeering and enhancement of drilling effciency.
  • Savings in rig time in settings requiring the TLC (Tough Logging Conditions) system and offshore. 
  • Multiple pass logging. Comparison logs made at different times can help distinguish pay from water zones, locate fluid contacts and identify true formation resistivity and density.
LWD is cost-effective when :
  • Rig cost is high. Rig cost high enough to make LWD attractive exists almost entirely offshore and where time-consuming TLC logging would be required. Most of the additional expense of a TLC operation is in rig cost, which run about $5000/hour in the North Sea. Amoco is looking to MWD/LWD as a means to cut this cost. Use of LWD may also accelerate selection of coring and casing points and perforation intervals, which can contribute to savings in rig time.
  • Water-base muds are used. These typically yield poorer borehole conditions by wireline time than oil-base mud (OBM). Wireline tools may therefore be difficult to get down the hole, may get stuck or yield poor logs.In the UK sector of the North Sea, as OBM use continues declining for environmental reasons, Amoco expects LWD use to increase. Use of OBM is banned in exploration wells in Norway and the Netherlands. 
  • The well is in an area known for operational difficulties -swelling shales or , most commonly in the North Sea , overpressured zones. Under these conditions, LWD offers the advantage of insurance logging. But more importantly, real-time data can accelerate decisions about well control and how the well should be driled and completed. Amoco finds that real-time data provide "an effective means of minimizing risk and reducing excessive operating costs" in exploration wells. Most of this savings is related to savings in rig time. To illustrate this point, Walsgrove cites an instance in which LWD reduced operating costs by allowing more accurate location of coring points within a sand/shale sequence. 
  • When real-time access to pore pressure analysis (in undercompacted formations) and petrophysical data are needed for drilling decisions and planning a wireline logging program and completion strategy. Real time access to petrophysical data has led to a new application, called geosteering- using real time measurement.

1 comment:

  1. Nice post,before reading your post i did not know about LWD technology,but now,i just read about this technology and it is really good.