okay so that's the oil and gas reservoir but many years ago the reservoir is actually this environment okay before it turns to be a reservoir they are actually some of them are river some of them are delta and some of them are lakes before they turn to be reservoirs They were Alufiel Fan, Braided River, Fan Delta, Continental Shelf, and so on and so forth. So they will become reservoirs in the future. So yeah, some people say it's thousands years ago or million years ago.
We are not sure. But before they turned to be reservoir, they were actually... Here, submarine fan, continental slope, delta, and so on and so forth. And of course they will have different properties, because they come from different depositional environment.
And as reservoir engineer and reservoir simulator, we need to understand the depositional environment of our reservoir. So if we want to simulate reservoir previously which which previously was river it will have different properties with reservoir that actually was a lake okay if we modeling reservoir which is now a river or channel reservoir of course the properties will be very different with reservoir that was a lake okay so we need to understand we need to discuss with our geologist friend, petrophysicist friend, geophysicist friend to understand the character of our reservoir. Okay and yeah before the hydrocarbon was formed, this slide is about reservoir formation.
How the reservoir forms. Bagaimana reservoir terbentuk. So previously we have something like mangkuk like this maybe, with mud, with sand, and land plants and animals that accumulated in this zone.
And accumulated across time, we have huge amount of deposits here, organic deposits, and somehow due to geological phenomena, layers of layers of sand will be at the top of this accumulation layer by layer will fill this accumulation and somehow this zone will become potential source rock it will become a kitchen, it will be a potential source rock which will cook the organic deposit, the organic accumulation, and change the organic deposit to be oil and gas. Okay, so after a very long period of time, this mud and sand becomes source rock, and it will be a kitchen. It will be a place to cook the oil and gas. And we have heat here.
we have heat and due to the burial we have high pressure high temperature and the oil and gas will form and somehow oil and gas will migrate go above due to permeability they will find the channel and then somehow they are trapped because there is a layer rock layer with very small permeability which is called seal right seal and because of this seal oil and gas cannot go above cannot go at upper zone and it will be stored here it will be trapped it will be accumulated in this layer and we call this layer reservoir oil and gas reservoir so that's the process of reservoir simple formation and this is another picture you see this source rock the gray color and then we have oil and gas generation here and the oil and gas are formed and then they migrate through this fault they find channel so that they can go up up and up and somehow they are trapped because of the seal rock here. We have seal rock, the purple line okay. And then they will separate the face will separate, gas will be at the top we call it gas cap, and then we have oil lake, and then we have water lake or aquifer okay.
And then between gas cap and oil lake we have gas oil contact. and between oil and water we have oil water contact all these terms are very very important so you need to be familiar with the term trap or seal or gas oil contact oil water contact gas cap aquifer you need to be familiar with those terms okay right again due to difference of density, okay difference of gravity, gas will be at the top and then oil and then the heaviest the water at the bottom okay they have different density and of course they will have different pressure at their corresponding depth okay so here we have gas and then oil and the water and they have different gradient. The slope of the line is different.
They have different gradient. Why? Because they have different density.
So they have different density, they will have different pressure gradient, and the line will be different. Gas will be quite steep, and then oil, and then water will be quite... mild okay landai okay and yeah during the oil and gas migration oil will migrate upwards because it is lighter whereas water will be pushed down because it is heavier okay so you know the hydrocarbon formation or reservoir formation okay And then we discuss about reservoir structure.