A horizontal fracture test was conducted in the McMurray Formation in the Athabasca Oil Sands 31 depths of 306 and 352 m. At these depths, the principal in situ stresses arc almost isotropic. The objective of the Lest was 10 develop a fracturing method to promote horizontal fractures for in situ recovery operations, and to identify the shape and extent of the fractures produced. A horizontal fracture in the Athabasca oil sands could be used to establish interwell communication between injection and produces, on a commercial spacing.
Three fractures were initiated in one well at two different depths. Two fractures were in the Basal McMurray Formation and the other was in the middle McMurray Formation. Hot water was used for the first fracture in the Basal McMurray; different coloured grout was used for the Other two, in order 10 distinguish the upper and lower fracture and to obtain a permanent record of the fracture path. Following the fracture program, six post-fracture core wells were drilled to locate the coloured cement grout in order LO define the geometry of the fractures. In addition, the following methods were used to monitor the fracture shape and extent:
One temperature observation well.
Two pressure observation wells
Surface tiltmeter survey
Electric potential survey
Precision surface elevation survey
Downhole borehole televiewer
Pressure and temperature in the injection Well.
One of the post fracture core wells intersected the coloured grout in the Middle McMurray. A group of hairline fractures, some without traces of the fracture fluid, were seen around the grout filled fracture as well as in two other post fracture core wells. During the fracturing process, pressure decreases of up to 70 kPa were measured in the observation wells. These observations are very unique and indicate that the fracture propagation mechanism In oil sands is very different in comparison to conventional hydraulic fracturing theory.
This paper will describe the results of the fracture tests With regard to the shape and extent of the induced fractures. The data from the various monitoring techniques will be compared to the geometry of the fracture Finally, there is a discussion on the fracture propagation mechanisms in low cohesion oil sands.
The Athabasca oil sand deposit is one of the world's largest bitumen deposit with in-place bitumen reserves of 1.14 × 100 m3. The deposit is located in the northern part of the province of Alberta Currently the Athabasca oil sands are mined commercially for bitumen extrusions. However the majority of the oil sands are 100 deeply buried for surface mining, therefore, in situ thermal recovery is methods are necessary. Typically, the bitumen density is 85 API, and the Thermal bitumen viscosity is 3.0 100 mPas at a reservoir temperature of 10 °C. In the zones o high bitumen saturation the initial cold water murices injection rate, at below fracture pressure, is normally about 2.0–5.0 m3/d. Although there are some areas of high injectivity, which needs to be fractured to achieve reasonable injection rates.