Analyzing fractured rock samples

A non-transitory computer-readable medium storing instructions which, when executed, cause a computer system to perform operations comprising:

• obtaining a first permeability measurement of a rock sample from a hydrocarbon reservoir at a first effective stress without exceeding the effective stress under reservoir conditions of the hydrocarbon reservoir;
• obtaining a second permeability measurement of the sample at a second effective stress without exceeding the effective stress under reservoir conditions of the hydrocarbon reservoir, wherein the second effective stress is greater than the first effective stress;
• obtaining a third permeability measurement of the sample at a third effective stress without exceeding the effective stress under reservoir conditions of the hydrocarbon reservoir, wherein the third effective stress is less than the second effective stress;
• and
• distinguishing between a natural fracture and an artificial fracture in the sample based on the first and third permeability measurements.

A system comprising

• a permeability measuring device configured to subject a rock sample from a hydrocarbon reservoir to an effective stress and to measure the permeability of the rock sample at the effective stress;
• and
• a controller connected to the permeability measuring device and configured to cause the permeability measuring device to perform operations comprising
• subjecting the rock sample to a first effective stress without exceeding a reservoir pressure of the hydrocarbon reservoir,
• measuring a first permeability of the sample at the first effective stress,
• increasing the effective stress on the sample to a second effective stress without exceeding the effective stress under reservoir conditions of the hydrocarbon reservoir,
• measuring a second permeability of the sample at the second effective stress,
• reducing the effective stress on the sample from the second effective stress to a third effective stress without exceeding the effective stress under reservoir conditions of the hydrocarbon reservoir,
• measuring a third permeability of the sample at the third effective stress, and
• distinguishing between a natural fracture and an artificial fracture in the sample based on the first and third permeabilities.