Downhole constant temperature difference thermal liquid flowmeter

Traditional liquid flowmeters have the disadvantages of low sensitivity, poor repeatability and low resolution when they are used to detect low flow rates in low-permeability oilfields. In this case, the accurate detection of low flow rate is the technical difficulty that needs solving urgently in domestic low-permeability oilfields. To solve this problem, this paper designed a DSP chip based thermal liquid flowmeter. This system is based on the principles of constant temperature difference and thermal diffusion. When liquid flows through a tachogenerator integrated with a heating resistor, the difference between the tachogenerator temperature and the environment temperature is kept constant by using the heating feedback circuit, the liquid flow rate is calculated by measuring the voltage of the heating resistor and the dynamic temperature control is conducted by means of the incremental PID algorithm, so as to realize the fast and stable flow rate measurement. Finally, the influence of environment temperature on measurement result was analyzed by performing lab experiments, and the operating performance of the instrument was verified. It is indicated that this flowmeter is more sensitive to the detection of low flow rate (0-5 m³/d) and its relative error is less than 1%, so it can realize the accurate measurement of low flow rate.