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Measuring tensile strength of unconventional shales using microwaving

Tensile strength is a critical parameter needed to plan hydraulic fracturing/crack initiation and propagation in reservoirs, especially in shale reservoir with complex natural fracture and fissure systems. Conventional methods for measuring tensile strength are either time consuming (direct tensile strength method) or unreliable (indirect method), and require precision “machined” samples and heavy mechanical instruments. We propose a new technique that measures the tensile strength of rock with low to extremely low permeability efficiently and accurately using microwave heating.
This method exploits the fact that when the temperature of water in a confined space, e.g., within a tight rock, increases, the pressure quickly elevates to the point where it exceeds the rock’s tensile strength and the rock breaks. Microwave heating can rapidly increase the temperature of water in the rock sample due to the relatively large dielectric loss of innate water. This method works well for rocks with low permeability where pressure leak off during the rapid heating is negligible.
This paper presents an alternative means for determining tensile strength of low permeability rocks: microwaving heating. We present both the theory and results of our initial laboratory tests, which we compared to conventional indirect tensile strength testing (Brazilian method). Microwaving of shales may crack and sometimes pulverizes the rock. When the sample is pulverized, we believe that 100% of the light hydrocarbons are released. Hence, the new method also may provide insight into total recoverable light hydrocarbons per kilogram.

Author(s):

Jin-Hong Chen    
Aramco Research Centers-Houston
United States

Bitao Lai    
Aramco Research Centers-Houston
United States

Dan Georgi    
Aramco Research Centers-Houston
United States