Falling head and constant rate injectivity and fracture tests, are conducted at the PCEJ project in the Athabasca Tar Sands to estimate effective permeability's and fracture parameters. The data and analyses for these three tests performed on a sample well are presented in this paper. In addition, the important considerations in the operating procedure and the advantages of running the tests in combination are discussed.
Different analytic techniques are used for each test data. A "DST" plot was made for the falling head test "Ramey and Homer" plots for the constant rate test and "Nolte and Homer" plots for the fracture test data. The numerical simulation model Tarfrac was also applied to compare the results.
In comparing the three methods, it was found that the calculated reservoir data matched reasonably well. Similarities were observed in the effective permeabilities and to a lesser extent, in the fracture leak-off and fracture length calculations. Convergence of the derived parameters showed that reliable permeability and fracture data could be obtained independent of the well test procedure and analysis used.
However, while the leak-off coefficient was consistent in the Nolte analytic model and the Tarfrac computer simulation, the calculated fracture closure time which depends upon the fracture width, was not consistent with field data. This variance indicates the methods of analysis are less suitable for modeling the physical properties of the fracture apart from the fracture length but are representative of fluid balance.
Although in-situ recovery from the McMurray formation in the Athabasca Tar Sands has been under test for many years, it has not yet been commercialized. The rich bituminous sands are deposited in varying geological conditions and they have very low pressure and native injectivity (Table 1). In currently active experimental projects, steam is either injected through horizontal wells, gas or water zones, or hydraulic fractures. Further testing and optimization in any of the ongoing projects could lead to economic recovery of the huge resource.
Injection fractures are utilized to heat the formation in the PCEJ Hanging stone pilot project. The formation n the area of operation is at an intermediate depth of 300 meters (1000 feet) where the fractures can be either vertical or horizontal. The formation thickness is roughly 30 meters (100 feet) and there are no major gas or water zones. In such a setting the heat distribution will be highly dependent on both the formation petrophysical properties and in-situ stresses. Various analytic and numerical studies are underway and special tests have been conducted to optimize the cyclic steam process in this project.
Presented here are three cold water injection field tests that are a part of the overall analyses program. (Actually four tests are run in combination but only three are discussed, as one of them. "The Minifrac" procedure, has been previously reported by Kry1.) In the initial "Falling Head Test"a bottom-hole tool is set and the tubing is filled with water. The formation response to the instantaneous charge of water is measured as the tool is opened.
