A method for monitoring slug flow in a subterranean well, the method comprising: at a time instant, transmitting an acoustic signal across a cross-section of a pipeline flowing multiphase fluid comprising gaseous fluid and liquid fluid, wherein a portion of the acoustic signal is carried through the cross-section of the pipeline by the multiphase fluid; receiving the portion of the acoustic signal carried by the multiphase fluid through the cross-section of the pipeline; determining an energy of the received portion of the acoustic signal carried through the cross-section of the pipeline by the multiphase fluid; and determining, at the time instant, a first quantity of the gaseous fluid and a second quantity of the liquid fluid passing the cross-section of the pipeline based, in part, on the energy of the received portion of the acoustic signal carried through the cross-section of the pipeline by the multiphase fluid and an energy of the transmitted acoustic signal, wherein determining the first quantity of the gaseous fluid and the second quantity of the liquid fluid comprises determining that the energy of the received portion of the acoustic signal carried through the cross-section of the pipeline by the multiphase fluid is substantially less than the energy of the transmitted acoustic signal and determining that the multiphase fluid comprises substantially more gaseous fluid than liquid fluid, wherein the energy of the received portion of the acoustic signal carried through the cross-section of the pipeline by the multiphase fluid decreases with an increased amount of the gaseous fluid. at a time instant, transmitting an acoustic signal across a cross-section of a pipeline flowing multiphase fluid comprising gaseous fluid and liquid fluid, wherein a portion of the acoustic signal is carried through the cross-section of the pipeline by the multiphase fluid; receiving the portion of the acoustic signal carried by the multiphase fluid through the cross-section of the pipeline; determining an energy of the received portion of the acoustic signal carried through the cross-section of the pipeline by the multiphase fluid; and determining, at the time instant, a first quantity of the gaseous fluid and a second quantity of the liquid fluid passing the cross-section of the pipeline based, in part, on the energy of the received portion of the acoustic signal carried through the cross-section of the pipeline by the multiphase fluid and an energy of the transmitted acoustic signal, wherein determining the first quantity of the gaseous fluid and the second quantity of the liquid fluid comprises determining that the energy of the received portion of the acoustic signal carried through the cross-section of the pipeline by the multiphase fluid is substantially less than the energy of the transmitted acoustic signal and determining that the multiphase fluid comprises substantially more gaseous fluid than liquid fluid, wherein the energy of the received portion of the acoustic signal carried through the cross-section of the pipeline by the multiphase fluid decreases with an increased amount of the gaseous fluid. determining that the energy of the received portion of the acoustic signal carried through the cross-section of the pipeline by the multiphase fluid is substantially less than the energy of the transmitted acoustic signal and determining that the multiphase fluid comprises substantially more gaseous fluid than liquid fluid, wherein the energy of the received portion of the acoustic signal carried through the cross-section of the pipeline by the multiphase fluid decreases with an increased amount of the gaseous fluid.