rangkuman dari sepm

7/25/2019 rangkuman dari sepm

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Rube Goldberg drew complicated contraptions to do simple tasks like the board game Mouse Trap

First thing you need is a kitchen...

Then you need a container...

Usually the kitchen and container are not connected, so you need plumbing...

Net you need to place the well in the right location

!" you miss the container a dry hole and no money

#ut i" e$erything %works& you get oil out o" the ground and money in the bank

#eing a bit more technical, we need

o 'ource rock rich in organic carbon that has the right temperature ( pressure conditions so

that the kinetics trans"orm organic matter into oil ( gas molecules

o Reser$oir rock with a trapping geometry capped by a sealing rock

o Migration pathways that allow the oil ( gas molecules to mo$e "rom the source to the trap on a

geologic time scale


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The kitchen is where organic matter dispersed within a source inter$al has undergone the

temperature)pressure history necessary "or oil and gas to be generated and epelled

'ource inter$als are organic rich. They are rated based on

o Their organic carbon content *T+ - total organic carbon and

o Their richness */! - hydrogen inde which controls oil $s. gas

Most source inter$als are shales

The best source rocks were deposited under reducing conditions with T+ o$er 012 carbon by weight*can be as high as 032


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4 reser$oir is a rock with enough porosity *pore space and permeability *connecti$eness that we can

produce *etract oil and gas out o" it

o Most reser$oirs are in clastic units o" sand5si6e or larger particles *sandstones, conglomerates

or in coarse carbonates *e.g., ree"s

4 trap is a 78 con"iguration in the subsur"ace that allows oil)gas to pool in signi"icant 9uantities

o Traps resulting "rom "aults or other structural "eatures are called structural traps they are the

easiest to recogni6e

o Traps resulting "rom the wedging out o" a reser$oir59uality rock, either due to depositional

thinning or post5depositional erosion, are called stratigraphic traps

'eals are rock layers that pre$ent leakage o" /s "rom the trap

o The most common seals are shales and e$aporites

o Top seal pre$ents leakage up through the top o" a reser$oir

o To ha$e a trap, we also need lateral seals so that /s don&t leak out o" the sides o" a trap

*usually more critical with stratigraphic traps.


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/ migration is the process o" mo$ing droplets o" oil and gas "rom the source to the reser$oir

o :rimary migration is getting the / out o" the source inter$al

o 'econdary migration is mo$ing the / in carrier beds and up "aults)"ractures to the reser$oir

Migration parallel to the depositional units occurs in sand and silt beds that ser$e as carrier beds

Migration "rom one stratigraphic le$el to another is called cross5stratal migration

o !t commonly occurs $ia "aults and "ractures

o Most cross5stratal migration is in an upward direction *buoyant "orces but depending on

pressure gradients /s can mo$e down into carrier beds i" the pressure gradient is downward.


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/ere is a cross5section through a sedimentary basin

The %granite& pattern represents non5sedimentary *basement rocks

There are ;01 ma


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!" we are working a basin in which "ields ha$e been disco$ered, we can %re$erse engineer& the /

system

o For eample, i" we know oil is in the shallow reser$oir on the right, we know / migrated into it

somehow

o 4s shown by the blue arrow, we might call upon / migration up the "ault

o This would connect our %kitchen& to our known "ield

o +" course we ha$e to consider the 78 basin geometry not a single cross5section

There are other elements to consider "or the / 'ystem

Timing did the trap eist when / migration occurred

o +b$iously i" / migration occurred be"ore the trap eisted, the trap will be empty or se$erely

under5"illed

Fill ( 'pill i" the trap $olume is small compared to the $olume o" generated /, then the trap has been

o$er"illed and ecess / has spilled


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o 'ince "ree gas displaces oil, an o$er"illed trap may hold gas while spilling oil

o The spilled oil could be trapped "urther up the o$erall migration path

o >e&ll see a cartoon eample o" this on the net slide

:reser$ation i" oil is trapped, there are conditions that can degrade the oil with time

o !" the reser$oir gets too hot, the oil can be cooked *cracked to gas

o !" the reser$oir is shallow and cool, bacteria can "eed o"" the oil and spoil *degrade it

This slide illustrates some basic concepts about / "ill and spill

Trap 4 is closest to the kitchen and will "ill "irst

o !t has a synclinal spill point on the right

o /s spilled "rom Trap 4 will migrate up to Trap #

o Trap # has a "ault leak point

Aarly charge "rom an oil5prone source consists o" oil with a minor amount o" gas

o Trap 4 starts to "ill with oil and dissol$ed gas


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4s time passes, signi"icant oil with a large proportion o" gas reaches Trap 4

o !" there is more gas than can be dissol$ed in the oil, then a "ree gas cap "orms

o The gas cap will displace oil, so only oil *with some dissol$ed gas will spill

A$entually the source will become o$er5mature, only generating gas

o !" enough gas reaches Trap 4, it will become entirely "illed with gas all the oil being displaced

*spilled

o Trap # now has a "ree gas cap and an oil leg, with oil spilling out o" Trap # at the "ault leak

point

:erhaps there is a Trap "urther up the migration path where oil spilled "rom Trap # is collecting

o 4 good eplorationist would start to search "or more traps up the migration pathway

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