Non-radioactive tracers to evaluate fracturing procedures

A method for evaluating gravel packs or frac packs in a wellbore, comprising:

• pumping a first proppant into the wellbore, wherein the first proppant comprises a first tracer comprising a first element selected from the group consisting of gadolinium, boron, and samarium;
• pumping a second proppant into the wellbore, simultaneous with or after the first proppant is pumped into the wellbore, wherein the second proppant comprises a second tracer comprising a second element selected from the group consisting of gadolinium, boron, and samarium, and wherein the second element is different than the first element;
• obtaining a post-fracture set of data in the wellbore using a pulsed neutron logging tool after the first and second proppants are pumped into the wellbore, the set of data comprising detector count rate data of thermal neutron capture gamma rays at a first time window of about 35 μs to about 150 μs and a second time window of about 200 μs to about 1000 μs;
• and
• analyzing the post-fracture set of data to determine locations of the first and second proppants in a gravel pack region in the wellbore, in induced formation fractures, or both by comparing a ratio of detector count rate changes of thermal neutron capture gamma rays at the first time window relative to detector count rate changes of thermal neutron capture gamma rays at the second time window to differentiate boron from gadolinium or samarium.