- [Voiceover] Upon the successful completion of this section on Sweet Spot Identification, the learner will be able to describe characteristics of Sweet Spots. Let's step back a minute and take a look at Sweet Spots, and let's define Sweet Spots from a geological perspective. So, from a geological perspective, a Sweet Spot in a reservoir is a place where there is preferential enrichment of hydrocarbons. And that can be due to a number of different factors, mainly increased porosity, and that has to do with either fracture networks and the oil and gas are within the fractures. Those fractures can be closed, and if that's the case, they're primarily storage and when they were migrating, the oil was migrating through, basically trapped there. They can be an other fractures, which means that the oil is essentially still moving through and is still potentially a migration pathway to the surface, to production. And so Sweet Spots can be due to improved sorting of grains, which results in better porosity. And also, Sweet Spots can exist due to diagenetic alteration resulting in A, connected pores, if there's been dissolution, so that there has been a dissolving of some of the matrix or some of the grains, and especially in carbonates. So you would have a disso, well, almost always in carbonates, but you could have dissolution and it could be vuggy porosity. Or you can also have diagenetic alteration of the magnesium elements and that would result in magnesium carbonate, and that would result in dolomitization and crystals. You would have intercrystalline porosity. If you've looked at all at hydrochloric fracturing and refracs, you a quite aware that the ultimate goal is to maximize conductive open fractures. So you want them to be open fractures. And they need to be connected and conductive, so they make great thoroughfares and conduits for the passage and flow of oil and gas. So we all know this. Okay, so this is good. Now the question, is from a geological standpoint, where did the open fractures come from, and where do the conductive open fractures come from? What precisely happened to create natural fractures that connect and conduct? Let's look at one explanation, and let's say they relate to the thermal maturation of kerogen and there are adsorption processes going on in this process. But they basically go back to the generation of hydorcarbons at the very beginning of the story. Let's take a look at how this happened. So what we're talking about is the generation of conductive fractures that occurred at the same time as the generation of hydrocarbons. So in the history of the basin, what you have is a so called "kitchen," and you have a kerogen, which is hydorocarbon-rich. But we have organic-rich kerogen. And we have burial, which results in overpressure. So we have pressure and we also have temperature. Sufficient temperature and sufficient pressure to quote, "cook" the hydrocarbons so that they, or cook the organic matter to turn it into primitive form of hydrocarbon, starting with gas. And then, like, not be too high-pressure and not to be too high-temperature, to burn it, but then also to be, have those conditions for sufficient time to mature it completely so that it's all the way to a hydrocarbon that's producible and it's not still sort of a wax or immature shale, or oil shale, or shale oil, depends on where you are looking at the reservoirs or the reserves. Any rate, let's take a look at expulsion mechanisms. So the kerogen exists, we have burial, and we have a maturation that results in phase changes. So as the kerogen is subjected to pressure and heat, it changes phase and goes into a gas. So the fluid, which is expanding due to the gas production, is overpressured. And the pressure creates micro-fissures. Those micro-fissures are, yes they are fractures. Nano-fractures. So stage one, the micro-fissures are created and they fill up with the hydrocarbon. The fissures are, at that point, closed. So they're just simply storage. And the second stage is in the second round of hydrocarbon generation. Another pulse of heat or pressure, or just more time goes on. There is more pressure and the fissures open up and they become nano, or micro-fractures. In the generation of hydrocarbons we need to understand the kinds of kerogen that can exist and their hydrocarbon potential. And, as we're looking at potential places for our Sweet Spots, we can take a look at total organic content. We can also take a look at the kerogen itself . And what we're really, really happy to find would be the aquatic kerogen, and that would be kerogen type one. And we see alginite, amorphous kerogen. And they primarily come from algal bodies. Think of algal mats, algal stromatolites, pond scum, slime. Wherever you see slime it's a good thing because it can generate oil. Now there can also be gas as well, just depending on the conditions of temperature and pressure. Now there are also kerogens type two which can be aquatic and terrestrial. And then three or four, which are primarily terrestrial and instead of having this lovely algal mat, algal stromatolite, tidal flat slime, you have more leaves and herbaceous plants or woody plants, things that you would potentially, eventually see as transformed into coal. You could also have oxidized, recycled woody debirs. Now, if you have kerogen type four, there's not going to be any hydrocarbon potential it's just going to turn into something else, and it could be all kinds of things but it's not going to be oil and gas. But two and three will have gas and some oil, or mainly gas. So this is important information, especially if you are say in China and you're looking mainly at lacustrine deposits. You're going to have mainly kerogen that's going to be gas productive. Very, very important, very critical information. So let's take a look at a thin section, and you can see porosity development. Now in this case I think what we're seeing is, is more of a dissolution. But also the, in theory, it's porosity that developed because of maturation and the pressure changes in expulsion. So notice before maturation there's a lot of organic matter and after, that organic matter has converted itself into hydrocarbon, and it's left open spaces, pore spaces, and it is also flowed out, or it could still have gas in it, but it has changed. So the organic matter conversion from kerogen into oil or gas, or both, has resulted in open spaces, or pore spaces. It could be conductive. It could be connected, but for sure, they can create places for storage for oil and gas, and this is basically the anatomy of a Sweet Spot.