Crossplots: 2005 #72 (similar)

Crossplots are on Guidebook 15 LOG 5.

X-Plots Advantages:
   Avoids calculating Sw for long logs.
   Can find Sw w/out m, Rw, or a porosity tool.
   Finds m, Rw, Δtma, ρma, rock types.
   Rw, and m can be varied w/out long calcs.

X-Plots Limitations:
   Large porosity range required.
   Cementation exponent m required.
   Matrix properties, & Rw must be constant.

Recognize these plots on-sight (the Guidebook has clear examples).
Hingle: saturation lines run from x-axis northeast
     matrix density is where lines converge to x-axis
Pickett: saturation lines run southeast to northwest
      𝐑𝐭 = Rw on 100% saturation line is when por = 1

An example of a Picket plot set a of data points (GB 15 LOG 5):



1) Find the 100% saturation line (through the most SW points); pick 2 points on line.
In this example, the line will pass through (porosity, Rt) points of (0.04, 5) and (0.1, 1).
2) Calculate the [log] of each point:
     Porosity = 0.04 [-1.4], Rt = 5 [0.7]
     Porosity = 0.1 [-1]; Rt = 1  [0]
3) Interpolate [log] values to Porosity = 1 (all water, no rock, so Rw = Rt).
     Por = 1 [0], Rt = 0.02 [-1.7]. Therefore, Rt = Rw = 0.02 ohm-m.

Given log-log paper? Plot & extend the 100% saturation line to porosity = 1 for Rw. It's easier.