• Partially gaseous and may contain some solids.
• Subject to large density changes, but this can be mitigated by installing an independent density meter.
•  Subject to significant viscosity changes under different operating conditions.
• Electrically conductive or non-conductive. 
• Operating in the laminar, transitional or turbulent flow regimes.

Given the similarity of these challenges, it is not surprising that a variation of the drilling mud flowmeter can be permanently installed to measure the production mass flow stream to enable faster diagnosis of operating issues and increase production.

Practical process control strategies not requiring production flow measurements were developed to manipulate the chemical injection flows in operating wells. These include:

• Manual adjustment of valves, pump strokes and pump motor variable speed drives.
• Self-contained chemical injection control valves (CICV).
• Measuring and controlling injection flows.
     o Closed loop feedback flow control with a flowmeter, flow controller and control valve (or variable speed drive) that maintains the desired flow rate of each chemical.
       o On/off control that opens and closes control valves for varying periods of time to achieve the desired total flow of each chemical.
  

Excerpted from Measuring Difficult Flow Streams and More Accurate Flow Control Can Improve Oil and Gas Well Profitability in Processing magazine.

One of the gases was fed from high pressure gas cylinders, while the other gas was generated in a process unit located approximately 100 meters from the flowmeters. Both flowmeters had sufficient straight run and were installed properly. There were pressure and temperature measurements downstream and upstream of the orifice plate respectively. Flow controllers were used to control the gas flows, and I seem to recall that a multiplier was used to ratio the flows.

Observation of the operation and its recordings revealed that the controlled flow rates of both gases were both controlling at set point, but the process gas flow was less steady than the cylinder gas flow. Both gas temperatures were steady. The pressure of the cylinder gas was steady and at its design pressure. However, the pressure of the gas from the other process unit would vary somewhat near its design pressure and occasionally drop off and recover a few minutes later.

As in many applications, the problem lies in more than one location. First and foremost, these flow measurement systems were not compensated for pressure and temperature variations.

The pressure of the gas from the cylinders should be compensated because even though it could easily be controlled, the pressure gauge used to control its pressure could be in error (or be read incorrectly) and cause significant flow error. The temperature of the gas varied with ambient conditions, so flow errors of a few percent were likely.

The most ominous problem was that of the process gas where the pressure at the flowmeter could vary between 60 to 120 percent of its design pressure and cause significant flow measurement errors. Even when steady, the operating pressure introduced errors because the pressure was only close to its design condition. Temperature variations were less dramatic than the cylinder gas, but could still produce measurement error. Pressure and temperature compensating this gas flow would mitigate the problem and likely eliminate the symptoms.

Pressure and temperature instruments for most flowmeters locate these measurements upstream and downstream of the flowmeter respectively. Note that the designer of this installation located the pressure transmitter downstream on the downstream tap of the orifice plate and the temperature transmitter upstream of the orifice plate. This did not cause problems with this particular installation (but it could with other installations) because orifice calculations were available for the downstream pressure tap location. The temperature transmitter location did not cause a problem because it was installed far enough upstream to not distort the velocity profile in the flowmeter and the temperature difference between the upstream and downstream locations was small.

It is apparent that the person(s) who designed this installation likely did not consider the need for pressure and temperature compensation, and if they did, they did not understand where the transmitters are commonly located. Recognizing that a temperature variation of 3ºC will alter the volume of a gas by approximately 1 percent at near atmospheric conditions, temperature compensation should be considered in virtually all gas applications. Similarly, relatively small pressure variations can cause significant volume changes, so pressure compensation should be considered in virtually all gas applications.

Even if it is decided not to pressure and/or temperature compensate the flowmeter, properly locate and install taps for a pressure and temperature transmitters. They are relatively inexpensive… and you never know when you will need them.

This article originally appeared in Flow Control magazine.

Viscosity is the ability of a fluid to flow over itself. Viscosity is dependent upon composition, temperature and the amount of stress applied to the fluid.

The composition of water is well-defined so its viscosity is also well-defined likely the lowest amongst these liquids. The composition of honey, mustard and peanut butter can vary such that (for example) “heavier” mustard could be more viscous than honey while “lighter” mustard could be less viscous. Peanut butter is likely more viscous than either honey or mustard. The correct answer appears to be Answer D.

Additional Complicating Factors

Complicating the above analysis is that temperature also affects viscosity whereby increasing temperature generally reduces the viscosity of the fluid. Therefore, increasing the temperature of peanut butter will reduce its viscosity. Conversely, decreasing the temperature of honey will increase its viscosity. Therefore, it is conceivable that the viscosity of hot peanut butter could be lower than the viscosity of cold honey.

Without more detailed investigation, Answer E may be the pragmatic choice.

This article originally appeared in Flow Control magazine.