One such application is the utilization of more accurate flowmeters to control chemical injection flows in oil and gas wells. In addition, modifying the control strategy to incorporate a mass flowmeter that measures well production can result in significant savings as compared to controlling chemical injection flows at fixed flow rates. Further, drilling rig safety and productivity can be enhanced by adding a mass flowmeter to measure drilling mud and related flow streams. Similar benefits can be achieved by applying the methodology presented herein to other processes.

When drilling wells, mud is pumped down to the wellbore and loose material is brought up to the surface where some of its components, such as gas and solids, are removed. The remaining material is accumulated in a mud tank where chemicals and other materials are added to modify its characteristics, such as density and viscosity, before pumping the modified mud down into the well.

If the well pressure becomes higher than the wellbore pressure, oil, gas and water can rush into the wellbore and create a well kick. This potentially dangerous situation can result in a sudden change in drilling rate, pressure fluctuations and drilling mud flow changes. If not mitigated, a well kick can develop into a blowout, which is an uncontrolled release of oil or gas. Well safety can be enhanced by installing a drilling mud mass flowmeter on the drilling rig to measure the flow of material coming out of the well. This measurement can provide a warning of a potential well kick and enable the operator to take timely action to prevent the impending kick and potential blowout, thus tending to decrease drilling rig downtime. For safety purposes, the required pressure rating of instrumentation in piping potentially subject to well kicks is typically 5,000 psig (345 bar) but can be higher or lower, depending on the well.

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

As for the replacement flowmeter --- the flowmeter was caught between constraints that would not budge.  First, the flowmeter should be located in a vertical pipe so that solid deposition would not be an issue.  That said, the piping had to be located within the boundaries of the pump house floor and the pump house ceiling.  Careful sizing revealed that there was (barely) sufficient space to locate the required straight run for the new flowmeter --- if the flowmeter run started at the floor and went to the ceiling. 

However, the discharge of the pump check valve and the pump house discharge pipe were at the same elevations about half way between the floor and ceiling.  In order to install the flowmeter in the vertical pipe, the pump check valve discharge piping would have to be routed down to the floor then up to the ceiling, and then down to the pump house discharge pipe.  Needless to say, this installation was considerably more expensive than locating the flowmeter in a horizontal run between the pump check valve and the pump house discharge. 

As such, there was extreme (political) pressure to locate the flowmeter in a horizontal run.  Standing your ground to get things right is not always easy.  Sometimes you have to go down to go up --- and then go down again. 

 This article originally appeared in Flow Control magazine.

The fluid velocities and Reynolds numbers at 10-100 gallons per minute are approximately 0.95-9.5 feet per second and 15,800-158,000 respectively. 

Most suppliers offer a 2-inch flowmeter (Answer A), so flowmeter size is not a problem.  The maximum velocity (Answer E) is well within the constraints of most vortex shedding flowmeters. 

In this application, Reynolds number will vary from approximately 15,800 to 158,000.  Operating at a Reynolds number as low as 15,800 (Answer B) may cause some vortex shedding flowmeters to operate non-linearly (Answer D).  However, operating at 0.95 feet per second (Answer C) will likely cause the typical vortex shedding flowmeter to turn off and measure zero flow. 

It should be noted that the velocity and Reynolds number constraints are interrelated.  The flow rate directly affects the fluid velocity and its operating Reynolds number --- both of which are constraints that must be satisfied for the vortex shedding flowmeter to operate properly.

Additional Complicating Factors

Analyzing flowmeter operation with a liquid exhibiting a higher viscosity that varies with temperature would further complicate this problem.

This article originally appeared in Flow Control magazine.