A system (801, 901) for performing a flash separation of a reservoir fluid, comprising: a sample chamber (805, 903) configured to hold the reservoir fluid; a flash apparatus, the flash apparatus comprising: a microfluidic device (833, 911) configured to flash the reservoir fluid, the microfluidic device (833, 911) in fluid communication with the sample chamber (805, 903) by means of an adjustment valve (827, 905) and comprising a serpentine microchannel having a micro-venturi, including a nozzle opening having a width smaller than that of microchannel, in an inlet thereof, wherein flashing of the reservoir fluid is initiated by one or more constrictions therein; and a separation chamber (835, 915) configured to separate the flashed reservoir fluid into a liquid phase and a gaseous phase, the separation chamber (835, 915) in fluid communication with the microfluidic device (833, 911) and comprising an inlet (843, 913) in fluid communication with the microfluidic device (833, 911) extending into a liquid phase of reservoir fluid in a liquid trap portion in the separation chamber (835, 915) and an outlet (847, 917) extending from above the liquid phase of reservoir fluid in the separation chamber (835, 915); and a gas receptacle (851, 919) configured to store the gaseous phase in fluid communication with the separation chamber outlet (847, 917). a sample chamber (805, 903) configured to hold the reservoir fluid; a flash apparatus, the flash apparatus comprising: a microfluidic device (833, 911) configured to flash the reservoir fluid, the microfluidic device (833, 911) in fluid communication with the sample chamber (805, 903) by means of an adjustment valve (827, 905) and comprising a serpentine microchannel having a micro-venturi, including a nozzle opening having a width smaller than that of microchannel, in an inlet thereof, wherein flashing of the reservoir fluid is initiated by one or more constrictions therein; and a separation chamber (835, 915) configured to separate the flashed reservoir fluid into a liquid phase and a gaseous phase, the separation chamber (835, 915) in fluid communication with the microfluidic device (833, 911) and comprising an inlet (843, 913) in fluid communication with the microfluidic device (833, 911) extending into a liquid phase of reservoir fluid in a liquid trap portion in the separation chamber (835, 915) and an outlet (847, 917) extending from above the liquid phase of reservoir fluid in the separation chamber (835, 915); and a microfluidic device (833, 911) configured to flash the reservoir fluid, the microfluidic device (833, 911) in fluid communication with the sample chamber (805, 903) by means of an adjustment valve (827, 905) and comprising a serpentine microchannel having a micro-venturi, including a nozzle opening having a width smaller than that of microchannel, in an inlet thereof, wherein flashing of the reservoir fluid is initiated by one or more constrictions therein; and a separation chamber (835, 915) configured to separate the flashed reservoir fluid into a liquid phase and a gaseous phase, the separation chamber (835, 915) in fluid communication with the microfluidic device (833, 911) and comprising an inlet (843, 913) in fluid communication with the microfluidic device (833, 911) extending into a liquid phase of reservoir fluid in a liquid trap portion in the separation chamber (835, 915) and an outlet (847, 917) extending from above the liquid phase of reservoir fluid in the separation chamber (835, 915); and a gas receptacle (851, 919) configured to store the gaseous phase in fluid communication with the separation chamber outlet (847, 917).