At
the heart of petroleum exploration is the RESERVOIR of oil and gas. No matter
what we do in E&P industry the reservoir is the focal point of the entire
decision making. In the coming blogs I will highlight how magnificently the
reservoir properties and financial decision making are linked. But today lets
focus on reservoir.
Three
parameters define the reservoir-
1.
Depositional
environment
2.
Structure of
reservoir and
3.
Diagenesis
Reservoir
rocks with some exceptions are generally sedimentary rocks.
There
are 2 main categories of sedimentary rocks
a) Silicicalstic
or the clastic- eg sand stones- Fields of North sea and Mehsana
b) Carbonates-eg
calcium carbonate – Fields in Saudi Arabia and Bombay offshore
The
characteristics of these sedimentary rocks vary according to their depositional
environment. This effects their porosity, permeability and saturation capacity
etc.
1.
Depositional
Environment
Depositional
environment can be defined as a area with a typical set of physical chemical
and biological process which result is specific type of rocks. Depositional environment
has a very strong correlation with production characteristics.
2.
Structure
The
earth surface is always in motion. The rocks are continually compressed and
stretched, resulting in deformities. Faults and folds are formed in the
subsurface can act as good trap for oil
and gas.
In
carbonate reservoir generally natural fractures are looked for oil and gas.
Fractures are considered pool of oil and gas thus drilling is done in natural
fracture as much as possible.
3.
Diagenesis
The
term diagenisis describes all chemical and physical process affecting sediment
after deposition.
This
includes
a) Effect
of pH
b) Effect
of oxidation
c) Overburden
pressure/ compaction
d) Cementation,
dissolution and replacement of rock particles.
Diagenesis thus affects the
permeability and porosity of the reservoir.
The Article is a bit difficult to comphrend. Reservoir rocks and sedimantry Rocks create confusion. Also places like mehsana are not as popular as saudi arabia. Moreover, Last three points of depositional environment,structure and diagenesis are not Clear.
ReplyDeleteThanks, for analyzing the article. As pointed out by you, i will soon write more on depositional environment and diagenesis. I will deal both these topics in detail in Geochemistry category.
ReplyDeleteAnd yes you are right that Saudi Arabia and Mehsana cannot be mentioned in same breath. But Mehsana field is famous. Not because of its production but because of its EOR. In terms of heave oil field Mehsana is a well known name.