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  1. Biodegradation Basics

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- [Oliver] Thank you so much. I'm going to talk about biodegradation and some other things, too. I want to specifically mention Jerimiah Forsythe who's picture is here. He's been running the 2D GC. We're going to see some 2D GC in today's talk. I'll explain what that is and he's the one doing the work. The outline is here. We're going to look at some of the basics of biodegradation, just very simple things. Then look at what happens when you have an oil column that's undergoing biodegradation, particularly with the diffusive process that's required. That's the... The reservoir is the Bhayam Reservoir in India. Then we'll look at 2D GC. The beauty of this giving chemical, distinct chemical peaks for individual chemical components of crude oil, the liquid phase of crude. And using that technique in downhole fluid analysis. We're going to look at a lot of different issues. Multiple charge, biodegradation, water washing in the Llanos Basin in Colombia. Then we'll look at a spill-fill sequence with biodegradation, water washing, and thermal maturity in the North Sea. The point really is that if you have all these different complexities taking place in these different reservoirs and they can all be unraveled. So downhole fluid analysis is measurements in the well bore using formation... waterline... Normally waterline formation testing tool. Then there's a lab measurement of the 2D GC which we'll get into. If possible, we'd like to have a petroleum system analysis of the basin to guide thinking on the processes that we're observing in these measurements. Some basics about biodegradation. First the microbes live in water, they do not live in oil. They dine at the oil/water contact, or the oil/water interface. And they need a lot of water because they have to get rid of waste and they need nutrients. So the water can't just be, uh, irreducible water in an oil zone. The microbes die if they get heated too much, so that 80 degrees C is the limit. So for a typical reservoir, if it's being buried, once it hits 80 degrees C, it gets sterilized, or so-called paleo-pasteurized, and then the bugs die and no more subsequent biodegradation. Then the microbes like different chemical components of the oil at, very differently. For example, they love n-alkanes, straight chain alkanes. We'll take a look at that. They do not eat the asphaltenes. They're smart that way. You won't have your asphalt roads biodegrading. The bugs don't like it. A typical scale is the Peters-Moldowan Scale. We work with Ken Peters all the time, who's the lead developer of the scale of biodegradation. Zero is no biodegradation. One refers to the munching of n-alkanes. This here means the alkanes are lost. The n-alkanes are lost. Here we see isoprenoids. They survive up to about 4 or so, then they start to disappear. So this is just a scaling of how things disappear. We will look at hopanes being converted to 25-norhopanes. That's in the Peters-Moldowan six range. So we can refer the extent of biodegradation from zero to in our studies six so far, with zero being no biodegradation and then it just getting more severe as you go down. The important thing though for an operator is not simply knowing whether or not the reservoir has biodegradation, it's known that biodegradation can increase viscosity considerably. The question is what is the viscosity profile in the reservoirs? This is the key point. In order to do that, we have to look in detail at what biodegradation does in the reservoir as opposed to just knowing that some biodegradation is taking place. All right, so a little bit more on biodegradation, n-alkanes, this n-C17 for example, refers to straight chain. This I'm showing n-heptadecane, that C17, 17 carbons. Isoalkanes are almost like the n-alkanes except with one methyl group, isoalkanes. The isoprenoids are built from isoprene which is a molecule that Mother Nature uses over and over. These compounds are the phyto group from chlorophyll that underwent different types of reactions in splitting off chlorophyll. These are very common in crude oil pristane and phytane. These are harder to biodegrade. So what people do all the time, we'll look at an example, is they compare the ratios of n-alkanes to these specific isoprenoids that are generally present in significant concentration. That ratio will change with biodegradation since the bugs eat this. This might be like the main course first then this is maybe something they don't- The vegetables, they don't like the vegetables so much so they eat less, to a lesser extent. So let's look at an example of this. This is the famous Oil Sands, probably the most famous biodegraded oil on the planet. Or at least amongst the most famous. It's very biodegraded and very well known, a large volume of oil. So what we have is the generation of oil in the foreland planes of the Rocky Mountains. The detritus, the erosion from the Rockies weights down the basin right here driving the source rock to lower incidence and getting heating and oil generation which then goes up away from this siding region near the mountains. Then you get an accumulation of oil in these places. You get shallower, and as you get shallower the reservoirs are colder and they undergo biodegradation. So what's typical, for example, is to look at the n-C17. So now that's a straight chain, that's heptdecane, versus the phytane ratio. So this oil is non-biodegraded. These are all from this Western Canadian Sedimentary Basin. This would be deep and hot, too hot for biodegradation. You can see the original ratio of n-C17 to pristane, and the n-C18 to phytane, and the n-alkanes are much bigger, but you can still see these isoprenoids. Then with modest or lightly biodegraded, then you can see that the isoprenoids pristane and phytane are growing relative to the n-C17. That is to say the n-alkanes are diminishing because the bugs are eating them. Here we're getting into moderate biodegradation. The alkanes are starting to get missing. The isoprenoids are still there. You can see that it's quite easy to see the biodegradation looking at the scale. Then when you get into heavy biodegradation all these peaks are reduced so that raises the baseline essentially, this undifferentiated mass of oil components. And severe biodegradation here. So that's the kind of thing that happens. We should be looking for that kind of easily observable transformation.

- [Oliver] Thank you so much. I'm going to talk about biodegradation and some other things, too. I want to specifically mention Jerimiah Forsythe who's picture is here. He's been running the 2D GC. We're going to see some 2D GC in today's talk. I'll explain what that is and he's the one doing the work. The outline is here. We're going to look at some of the basics of biodegradation, just very simple things. Then look at what happens when you have an oil column that's undergoing biodegradation, particularly with the diffusive process that's required. That's the... The reservoir is the Bhayam Reservoir in India. Then we'll look at 2D GC. The beauty of this giving chemical, distinct chemical peaks for individual chemical components of crude oil, the liquid phase of crude. And using that technique in downhole fluid analysis. We're going to look at a lot of different issues. Multiple charge, biodegradation, water washing in the Llanos Basin in Colombia. Then we'll look at a spill-fill sequence with biodegradation, water washing, and thermal maturity in the North Sea. The point really is that if you have all these different complexities taking place in these different reservoirs and they can all be unraveled. So downhole fluid analysis is measurements in the well bore using formation... waterline... Normally waterline formation testing tool. Then there's a lab measurement of the 2D GC which we'll get into. If possible, we'd like to have a petroleum system analysis of the basin to guide thinking on the processes that we're observing in these measurements. Some basics about biodegradation. First the microbes live in water, they do not live in oil. They dine at the oil/water contact, or the oil/water interface. And they need a lot of water because they have to get rid of waste and they need nutrients. So the water can't just be, uh, irreducible water in an oil zone. The microbes die if they get heated too much, so that 80 degrees C is the limit. So for a typical reservoir, if it's being buried, once it hits 80 degrees C, it gets sterilized, or so-called paleo-pasteurized, and then the bugs die and no more subsequent biodegradation. Then the microbes like different chemical components of the oil at, very differently. For example, they love n-alkanes, straight chain alkanes. We'll take a look at that. They do not eat the asphaltenes. They're smart that way. You won't have your asphalt roads biodegrading. The bugs don't like it. A typical scale is the Peters-Moldowan Scale. We work with Ken Peters all the time, who's the lead developer of the scale of biodegradation. Zero is no biodegradation. One refers to the munching of n-alkanes. This here means the alkanes are lost. The n-alkanes are lost. Here we see isoprenoids. They survive up to about 4 or so, then they start to disappear. So this is just a scaling of how things disappear. We will look at hopanes being converted to 25-norhopanes. That's in the Peters-Moldowan six range. So we can refer the extent of biodegradation from zero to in our studies six so far, with zero being no biodegradation and then it just getting more severe as you go down. The important thing though for an operator is not simply knowing whether or not the reservoir has biodegradation, it's known that biodegradation can increase viscosity considerably. The question is what is the viscosity profile in the reservoirs? This is the key point. In order to do that, we have to look in detail at what biodegradation does in the reservoir as opposed to just knowing that some biodegradation is taking place. All right, so a little bit more on biodegradation, n-alkanes, this n-C17 for example, refers to straight chain. This I'm showing n-heptadecane, that C17, 17 carbons. Isoalkanes are almost like the n-alkanes except with one methyl group, isoalkanes. The isoprenoids are built from isoprene which is a molecule that Mother Nature uses over and over. These compounds are the phyto group from chlorophyll that underwent different types of reactions in splitting off chlorophyll. These are very common in crude oil pristane and phytane. These are harder to biodegrade. So what people do all the time, we'll look at an example, is they compare the ratios of n-alkanes to these specific isoprenoids that are generally present in significant concentration. That ratio will change with biodegradation since the bugs eat this. This might be like the main course first then this is maybe something they don't- The vegetables, they don't like the vegetables so much so they eat less, to a lesser extent. So let's look at an example of this. This is the famous Oil Sands, probably the most famous biodegraded oil on the planet. Or at least amongst the most famous. It's very biodegraded and very well known, a large volume of oil. So what we have is the generation of oil in the foreland planes of the Rocky Mountains. The detritus, the erosion from the Rockies weights down the basin right here driving the source rock to lower incidence and getting heating and oil generation which then goes up away from this siding region near the mountains. Then you get an accumulation of oil in these places. You get shallower, and as you get shallower the reservoirs are colder and they undergo biodegradation. So what's typical, for example, is to look at the n-C17. So now that's a straight chain, that's heptdecane, versus the phytane ratio. So this oil is non-biodegraded. These are all from this Western Canadian Sedimentary Basin. This would be deep and hot, too hot for biodegradation. You can see the original ratio of n-C17 to pristane, and the n-C18 to phytane, and the n-alkanes are much bigger, but you can still see these isoprenoids. Then with modest or lightly biodegraded, then you can see that the isoprenoids pristane and phytane are growing relative to the n-C17. That is to say the n-alkanes are diminishing because the bugs are eating them. Here we're getting into moderate biodegradation. The alkanes are starting to get missing. The isoprenoids are still there. You can see that it's quite easy to see the biodegradation looking at the scale. Then when you get into heavy biodegradation all these peaks are reduced so that raises the baseline essentially, this undifferentiated mass of oil components. And severe biodegradation here. So that's the kind of thing that happens. We should be looking for that kind of easily observable transformation.