Porosity calculations are shown on a single GB page: 15 LOG 4. It starts:
Total Porosity: (measured with nuclear tools).
…equals primary porosity + secondary porosity.
Primary Porosity (apparent, intergranular).
Found from Wylie’s (acoustic) porosity equation below.
Secondary Porosity (isolated pores, vugs, and fractures).
also called diagenetic porosity.
…may be overlooked by acoustic-logs.
…equals total porosity – primary porosity.
At a glance, it's easy to see diagenetic porosity is found by nuclear tool porosity minus sonic porosity.
In this problem, nuclear tool porosity is given: 20 pu, and a sonic tool slowness of 79 microseconds/ft over the zone. The known slowness in sandstone & oil (shown in the GB variable box) are 55.5 & 232 microseconds/ft.
Wylie's Equation is next in the GB:
Por sonic = (dt - dtma)/(dtf - dtma) = (79 - 55.5)/(232 - 55.5) = 13 pu.
Since diagenetic = secondary = total - primary: 20 - 13 = 7 pu.
So since the 2020 reference guide doesn't mention that oil is 232 us/ft and water is 189 us/ft does that mean they would give those values to us or this type of problem wouldn't be on the exam?
ReplyDeleteYes. No.
DeleteJust my opinion: I wouldn't let what is in the Reference guide direct your studying. As you point out, testers can add anything at will and would be amiss if they ignored so much of what is in the SPE literature that is not in the RG. So when studying, I would just make sure to know the RG for quick access but use other resources doing the practice problems. The object is the learn the material and problems and the only way to do this is to use ouside resources.
I think the test will be very fair, and when you get to a problem you don't know, you will be thinking: hey, I should know this without any references, this is on me :-). But I've been wrong before...