Laboratory investigation on stress sensitivity of carbonate reservoir considering vuggy connectivity
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Abstract:
Due to the changes of pressure, fractures intersected with borehole open and stress sensitivity happens in the progress of drilling, which make the diameters of solid materials unmatched to the loss channels and aggravates mud loss controlling. The existence and connectivity of vugs affect the variation range of fracture width. Carbonate outcropping core samples with different vug types are taken as laboratory subject. Experimental results including 6 groups rock samples shows that stress sensitive coefficients of the single vug(5 mm), single vug(10 mm), double vugs(5 mm, disconnected), double vugs(5 mm, connected), double vugs(10 mm, disconnected), double vugs(10 mm, connected) core samples are respectively 0.66, 0.59, 0.47, 0.24, 0.66, 0.43, and the degree of stress sensitivity is respectively medium to strong, medium to strong, medium to weak, weak, medium to strong, medium to weak. It shows that the vugs intensify the rangeability of fracture width and the stress sensitivity. Though the vuggy connectivity weakens the stress sensitivity of fractures, it destabilizes the plugged zone and fails in lost circulation controlling, which causes severe lost circulation.
