Page 103 - Fundamentals of Gas Shale Reservoirs

CENOZOIC RESOURCE SHALE EXAMPLE 83

Gamma ray pro le
Brown shale @ karbindo quarry
m.
Wall “A” Wall “B” Wall “C” Rock samples
220 220
215 Intercalation of high laminated
210 210 shale and massive mudstone
205
200 200
195
190 190
185 Massive mudstone (light brown
180 180 color, high grade of competence)
175
170 170
165
160 160 Fossiliferous shale
155
150 150 (fossils laminations)
145
140 140 Massive mudstone (light brown
135 130 color, high grade of competence)
130 120 Fossiliferous shale
Stratigraphic section (m) 115 110 Massive mudstone (light brown
125
(fossils laminations)
120
110
color, high grade of competence)
105
100
100
95
(fossils laminations)
90 90 Fossiliferous shale Shale Fossiliferous shale
Massive mudstone
85 80 Massive mudstone (black Siltstone (silt/clay)
80 color, low grade of competence)
75 70 Limestone High fossiliferous
70 Silty dark shale mudstone
65 60
60 High fossiliferous black mudstone Black coal Silty shale
55 50 (gastropods)
50
45 40 Massive mudstone (black
40 color, low grade of competence)
35 30
30 Black to dark gray shale
25 20
20
15 10 Calcareous siltstone (light brown to light gray color)
10
5 0 Intercalation of blocky black coal
0 and ne grain limestone (light brown color)
0.0 50.0 100.0 150.0 200.0 250.0 300.0
Clay Silt Fine Medium Coarse Gravel
Gamma ray values counts/s Grain size
Mud Sand
FIGurE 4.16 Measured stratigraphic section and outcrop gamma ray log of the Brown Shale in Sumatra, Indonesia. The three‐colored
intervals of the gamma ray log indicate three different measured sections combined into this composite log. Arrows denote sequences and
systems tracts. Permission to publish this figure was provided by Brito (2014).
and RHP variations provide a subdivision into a number source rock for many of the younger, stratigraphically
of higher frequency depositional sequences; one possible shallower reservoirs there (Katz and Dawson, 1997). It
interpretation is provided in Figure 4.16. has been interpreted as a lacustrine, syn‐rift shale by Katz
and Dawson (1997). There are very few wells that have
penetrated the Brown Shale, and to our knowledge, there is
4.8 CENOZOIC rESOurCE SHaLE EXamPLE only one lengthy outcrop within the active Karbindo coal
mine. Along the vertical mine walls, an outcrop gamma
Examples of Cenozoic resource shales are not common, per­ ray log was obtained along with outcrop description; these
haps because many of them have not been sufficiently buried measurements revealed increased gamma ray log response
to be geochemically mature. One shale of current interest is in the lower portion of the lower zone, followed upward by
the Eocene‐Oligocene Brown Shale, which occurs in a variable gamma ray response in the upper interval of the
Sumatra, Indonesia; it is thought to be the major hydrocarbon lower zone (Fig. 4.16).