Three-dimensional modeling and reservoir visualization tools are increasingly used to add value to California heavy oil projects.
That was the message of two geologists who presented a paper on the subject at the recent Pacific Section meeting.
Steven J. Sanford, a geologist at the Chevron Production in Bakersfield, Calif., said he utilizes these tools for three main functions:
- Modeling and visualization.
- Planning horizontal well paths.
- Building reservoir monitoring data.
"In the past, our simulation models were farmed out to our research department," Sanford said. "The process was technically difficult and arcane, and might take several weeks or months to complete.
Now, however, thanks to user friendly improvements in the software -- which is part off-the-shelf and part Chevron, Sanford said. "Geologists like myself can build most models without the need for waiting to have it done by research.
"It's not because I've become smarter than the researchers," he added, "but rather the tools involved are so powerful and simple to use. I can build a model in the morning and be running numerical simulations in the afternoon."
Sanford acknowledges that he still needs the physical properties not captured by the model itself, as well as various geological, structural, log and other interpretations. And he says that really sophisticated and complicated modeling would still have to go to research.
But for the relatively small models relating to steam injection, which he handles, the new tools are great time savers.
Time Is Money
These interactive tools also help draw the well paths that satisfy all the mechanical and geologic restraints of drilling operations and reservoir conditions. This reduces the risk in guiding the well path through the optimum part of the reservoir.
"In the past, when we were using a paper map, you would outline points, then find out you had to move path locations -- and there might be several iterations going back and forth among different people," Sanford said. "But now the 3-D interactive tools accomplish this with a significant reduction of cycle time -- as well as the increased confidence that the well path chosen is the best one."
The capacity to visualize reservoir monitoring data also represents a great improvement from the previous method of paper plotting X, Y and Z coordinates to determine optimal relationships between temperature peaks and steam injections.
Sanford noted how you need the steam to operate the wells, but if the steam is too hot it makes it difficult, if not impossible, to lift the oil. Now a diskette with the temperature data from the contractor is loaded -- and fifteen minutes later the relationships are visible on the screen.
"The optimum temperature for the steam is 200 degrees Fahrenheit," Sanford said. "But on one recent occasion, we saw it was 220 degrees Fahrenheit, so all it took was a phone call to reduce the temperature, increase oil production and save money."
How much additional oil is garnered through these tools?
"The benefits can't be clearly demonstrated," Sanford said, "but my guess is that there are incremental gains of about 15 percent. And the process is certainly much quicker."
Sanford's colleague, geologist Nancy A. Wildman, explained that fiber optics are utilized to measure the temperatures in steam injection, and it is the internal reflection of the fiber optics that capture the temperatures that are translated to the 3-D model on the computer screen.
Sanford added that his present tools also do a better job representing reservoir properties and correlating them one to the other.
The areas being explored here are the Cymric and Coalinga Fields in the San Joaquin Valley, Calif. Related work in the Miocene Temblor Sands of the West Coalinga Field, in terms of seismic imaging of thermal enhancement processing, is being done by geologist Ed Von Dohlen.
The software used to significantly reduce 3-D interpretation time is VoxelGeo, from Paradigm Geophysical, Houston.
Von Dohlen said that this off-the-shelf tool, originally designed for medical MRI types of analyses, is set up for the interpretation of the seismic data, from which it is possible to measure the performance of the steam flood.
He said that the reservoir sand in the Coalinga Field is made up of channels and delta lobes that tend to be laterally discontinuous. These sands have a sinuous characteristic to their flow and ordinarily are not amenable to accurate interpretation.
"This application is very quick, and shows the interrelationships of the various sands you are processing," Von Dohlen said. "The steam processing directly correlates with the high amplitudes on the horizons, so it's a conceptual leap to be able to see in 3-D that aspect of the processing sand that you are generally not able to see."
Now, Von Dohlen said, he is able to assemble data into a 3-D image so he can actually visualize how the heat front is moving through the sands.
"We've been able to correct out of zone injections as well as to more uniformly place the injections across the sand unit," he said. "Without this application, we would not have the understanding of how the sands interconnect and the relationship of the injector to the producer.
"The result is significant production gains -- about a 50 percent increase with the same amount of injection."
In short, a clearer understanding of the complex stratigraphy derived from the 3-D and 4-D seismic data is being used to help improve efficiencies in steam injection programs.
"If successful, this type of seismic integrated analysis could have immediate impact throughout thermal drive projects," Von Dohlen said, "by reducing drilling costs, controlling steam break through and allowing for better management of both the reservoir and steam injection."
Sanford added that the 3-D modeling and visualization efforts going on in his department "represent only one small corner of Chevron.
"Similar experiments, some of them even more advanced, are taking place all throughout the company."