Abstract: The invention relates to a method of measuring pressure in which an evacuated capsule (1) containing a resonant element (5) is placed in the fluid whose pressure is to be measured, a vibration characteristic of the element is measured, and the pressure is deduced from said characteristic. A resonant element is used which, during measurement, is to be found in a stress state that is close to buckling. For this purpose, it is possible to use heater means for heating the element and servo-controlled so as to keep the frequency of vibration thereof constant. The resonant element can be made of silicon. The invention is particularly applicable to oil wells.

Abstract: Micro-Electro Mechanical Systems (MEMS) based fluid sensors adapted to measure physical properties of oilfield reservoir fluids under downhole conditions. Certain embodiments of the invention may be characterized as a MEMS based reservoir fluid sensor adapted for downhole conditions having a planar member machined from a substrate material, an electrical conductor formed at least partly on the planar member; and a gauge formed on the planar member and adapted to measure a physical effect on the planar member, the physical effect being indicative of a property of a fluid in contact with the planar member.

Abstract: The invention relates to a device for measuring the flow rate Q of a fluid in a fluid passage, in a well, the device comprising a first venturi section and first means responsive to the pressure difference .DELTA.P.sub.1 across the first venturi section between two points that are separate from each other in the flow direction. It comprises a second venturi section, and second means responsive to the pressure difference .DELTA.P.sub.2 across the second venturi section between two points that are separate in the flow direction, the two venturi sections being disposed relative to each other in such a manner that for a given direction of fluid flow, the diameter of one of them increases whereas the diameter to the other one of them decreases, said venturi sections being further arranged in such a way that the static pressure components present in said pressure differences .DELTA.P.sub.1 and .DELTA.P.sub.2 can be cancelled out.