1. Reservoir Setting & Dielectric Model

- [Dick] Good morning, this is Dick Merkel. I'd just like to welcome you all to this presentation. The topic is advanced field log interpretation and field development. This was presented in Iceland last summer by Margaret Lessenger and myself. This is the title slide for our presentation there. The paper is in the transactions at SPWLA. I believe it's It has been revised and added onto and down at the bottom in red down here you can see that it's published in the petrophysical journal, October journal, volume 57 number 5. And all the figures that you will see with I think one exception is going to be in that paper. So if anybody's really interested in this topic, they can go into the latest issue of petrophysics and look at it. And what we're gonna talk about today from an outlying standpoint is I'm gonna be having a little slight introduction to what the problem was and why we wanted to use dielectrics to solve the problem in field development. And interpretation, reservoir and non-reservoir rocks and how we use these data to do that interpretation. I'll give two examples, one in depleted reservoir, one in an over-pressured reservoir. Discussions and conclusions. So at any rate, what we have in terms of a problem was in Utah in the Uintah Basin there's a lower green river sand which is eocene in age, lacustrine in nature, and the fluvial sandstones. And what we wanted to do is evaluate that reservoir. It's a very large field. It's 100,000 acres as you can see in the second bullet point. One of the issues is that the section that we're looking at in the lower green river section are these fluvial sands come and go and they're 25 co-mingled sands that are identified by our geologic environment. And all those were co-mingled in the reservoir. And it's high paraffinitic wax. If anybody has seen the oil that comes out of Uintah Basin, it's like shoe polish at room temperature. It has a viscosity of somewhere in the order of about four centipoise at reservoir conditions, but at surface temperatures it's basically a solid. There was a water flood started in 1987 by Lomax who is the owners of the particular, at that time. The idea was to see if they could move some of that oil around. I'm not sure that they ever were able to justify doing that, so the water flood operation was pretty much put on hold until New Field took over and started a robust water flood, mostly for pressure maintenance. And one of the reasons was that the reservoir is just above bubble point, and you can see in some of the plated slides later on that once we get below bubble point we start making a lot of gas. The pressure maintenance was critical. One of the issues that we had was that we were going from a 20 acre spacing in the reservoir to a 10 acre vertical spacing, and that got approved by the state legislatures. One of the questions was, and the last bullet point, can you identify the breakthrough? So we put our heads together to try to figure out how we could identify the breakthrough from the water flood and all these various sands. So what we did is decide to go to a dielectric system because the water flood was a very fresh water that we're putting in there and we figured that we could, with a dielectric tool we might be able to determine what the difference was between the connate water, which was about 25,000 ppm, equivalent NACL, and the flooded water which was about 8,000 to 10,000 ppm, equivalent NACL. And if we could see that changes in resistivity, if the well bore in the new wells that we're drilling on the 10 acre spacing then we oughta be able to determine that that particular sand has been totally flooded. We do not want to perforate that particular zone. So we looked at this dielectric tool as a way of doing this. And this particular slide shows you what the real component of the dielectric constant of water is, as a function of water salinity. Where we were of course is down in this range between zero and 50, but the connate water is about 25 and at 150 degrees Fahrenheit. So you can see that the dielectric constant of the real component of the dielectric constant is that water was about 62 or 63. Conversely, if you look at the imaginary part of the dielectric constant at 150 degrees you have a fairly substantial component, but you're down here where the imaginary part of the dielectric constant, it gets very, very small. Was really the real component that we were mostly interested in, or have to worry about, but we also of course had to look at the imaginary part too and take the vector sum of these two things to calculate what the dielectric constant of the water is. It's interesting to note that if you're down around 10,000 ppm from the injected water, the imaginary part is almost nil.