Difference between revisions of "True resistivity determination"

From AAPG Wiki
Jump to navigation Jump to search
Line 31: Line 31:
 
! Then…
 
! Then…
 
|-
 
|-
| Bed is <20 ft thick for an induction log or <4 ft thick for a laterolog
+
| Bed is < 20 ft thick for an induction log or < 4 ft thick for a laterolog
 
| Correct for this bed using appropriate service company chart
 
| Correct for this bed using appropriate service company chart
 
|-
 
|-

Revision as of 19:28, 6 March 2014

Exploring for Oil and Gas Traps
Series Treatise in Petroleum Geology
Part Predicting the occurrence of oil and gas traps
Chapter Predicting reservoir system quality and performance
Author Dan J. Hartmann, Edward A. Beaumont
Link Web page
Store AAPG Store

The true resistivity (Rt) of a formation is its resistivity when not contaminated by drilling fluids. It may contain formation water only (Sw = 100%) or formation water and hydrocarbons (Sw t is fundamental when analyzing well logs for the presence of hydrocarbons. For a discussion of resistivity concepts see Asquith, 1982.

How invasion affects rt measurement

During the drilling process, filtrate water from the drilling fluid invades the formation. Its resistivity (Rmf) is either greater than, less than, or equal to Rt and can distort deep resistivities. Distortions to resistivities due to invasion must be corrected to get a valid Rt value. The diagram below shows resistivity profiles of formations with fresh and saltwater mud filtrate invasion.

Figure 9-29 See text for explanation.

Obtaining a valid rt value

To obtain an uninvaded zone resistivity (Rt)

  1. Read the resistivity of the log with deepest investigation (ILD, LLD, etc.).
  2. Use the table below to determine how to make corrections.
If… Then…
Bed is < 20 ft thick for an induction log or < 4 ft thick for a laterolog Correct for this bed using appropriate service company chart
Bed is shallow, medium, and deep investigating tools measure, different resistivities (i.e., log has step profile) Correct for invasion using appropriate service company tornado chart

See also

External links

find literature about
True resistivity determination
Datapages button.png GeoScienceWorld button.png OnePetro button.png Google button.png