Methods and networks to determine a boundary of a cement mixture

A computer-implemented method to determine a boundary of a cement mixture deposited in a wellbore, the method comprising:

• receiving first acoustic signals transmitted from at least one of a first plurality of acoustic tags mixed with cement deposited along a first section of a wellbore in an annulus between a casing and the first section of the wellbore, wherein the first acoustic signals are transmitted within a first frequency range;
• receiving second acoustic signals transmitted from at least one of a second plurality of acoustic tags mixed with a first substance deposited in a second section of the wellbore, the first substance and the cement having different material properties, and the first substance being separated from the cement along a first boundary of the cement, wherein the second acoustic signals are transmitted within a second frequency range;
• determining a location where acoustic signals having two different frequency ranges are detected;
• and
• determining a location of the first boundary of the cement based on the location where acoustic signals having two different frequency ranges are detected.

A downhole acoustic communication network, comprising:

• a first plurality of acoustic tags mixed with cement deposited along a first section of a wellbore in an annulus between a casing and the first section of the wellbore, each acoustic tag of the first plurality of acoustic tags being operable to transmit acoustic signals within a first frequency range;
• a second plurality of acoustic tags mixed with mud deposited in a second section of the wellbore, each acoustic tag of the second plurality of acoustic tags being operable to transmit acoustic signals within a second frequency range;
• at least one acoustic detector deployed along the casing, each detector of the at least one detector operable to:
• detect acoustic signals from at least one of the first plurality of acoustic tags mixed with a cement slurry and the second plurality of acoustic tags, wherein the first acoustic signals are transmitted within a first frequency range, and wherein the second acoustic signals are transmitted within a second frequency range;
• and
• store the acoustic signals in a storage medium component of the respective detector;
• and
• a controller operable to:
• determine a location where acoustic signals having two different frequency ranges are detected;
• and
• determine a location of a first boundary of the cement slurry based on the location where acoustic signals having two different frequency ranges are detected.