A spinner flowmeter is a rotating element device used in a well to measure flow rate, much the way a water meter measures flow in a pipe. Downhole flowmeters were in use in the 1940's. The original rotameter float tools were run on slickline, and recorded downhole by scribing on a clock driven chart. The clever use of clock driven magnetic tape and a bar magnet attached to the shaft of a propeller or turbine became possible after World War II, also purely mechanical tools run on slickline. The magnetic tape was analyzed under a microscope after the tape was sprinkled with iron powder. Increasing use of electric wireline logging allowed experimentation with not only the propeller and turbine elements, but also hot wire anemometers, doppler sonic elements, pitot tube pressure elements, and eddy shedding vortex elements. But the propeller and turbine tools are the major survivors in current widespread use. The first spinner flowmeters were almost all equipped with a packer or deflector device of some kind. These gradually disappeared until they were largely unavailable from service companies by the mid 1960's, but more recently, deflector type spinners have reemerged because of the advantages they offer in low and/or multiphase flow.Some Pointers
Today "spinner flowmeter" generically refers to any tool using a fluid rotated element, propeller (a/k/a vane type) or turbine (a/k/a helical type). Two major categories exist, "axial spinners" where flow parallel to the long axis of the tool is measured, and "tangential spinners" often used to measure flow from perforations (tangential spinners always use turbine elements). Axial spinners are further broken down into three subcategories: (1) "continuous spinners" where the spinner is no larger than the maximum tool diameter, named for its use in continuously run surveys (stationary measurements can also be made), (2) "fullbore spinners" where the propeller element can expand larger than the tool diameter, the name deriving from an old Schlumberger trademark (patent now expired), and (3) "diverting spinners" where a packer or basket of some type diverts flow into the barrel of the tool and past the spinner element.
Pulses are generated with each revolution of the propeller or turbine element; many different pulse rate schemes exist (anywhere from one or two pulses per revolution up to ten or more). Originally mechanical coupling was used, but more modern tools use either a magnetic or optical pickup to get the rotational information to the tool electronics. Some spinners have electronics capable of indicating flow direction, a nice feature when doing crossflow surveys. Typically turbine type elements are suspended between jeweled bearings, one of which is usually adjustable. A turbine should rotate freely without wobbling when gently blown.
Spinner log interpretation is predicated on a linear relationship between spinner rotation speed and fluid velocity. Spinner tools should therefore generally be run centralized. A decision must be made if well conditions are conducive to running a useful log, especially when running the continuous spinner in relatively low flow rate wells. The flow rate should be reasonably constant and of sufficient volume for the particular type of instrument being used. Flow should be turbulent in most of the well as spinners become nonlinear at low flow rates. Dynamic logging (the tool is moving) may help in slow flow situations, but the fluid velocity must still be large enough compared to the tool velocity counts to provide reasonable resolution. Dirty fluid is death to spinner tools and can foul the bearings; magnetic corrosion products in the wellbore can foul the magnetic sensing mechanism in some tools.
Spinner surveys are often used for production profiling and to a lesser extent for injection profiling. There are many different types of spinner surveys. The multipass or in-situ calibration technique is probably the most accurate. It involves at least two up and two down logging passes at different speeds (some authorities say at least three passes in each direction). The two pass overlay method was developed by Schlumberger for use with their fullbore spinner. Singe pass surveys are the least reliable, but are common. Single pass logs will not work in open holes (shot holes) and the other methods require caliper data to be useful in open hole environments. The horizontal spinners allow flow from perforations to be examined; Bell made some continuous spinners that are field convertible to horizontal configuration.
Well conditions must be suitable; sufficient flow, stable flow, and clean fluids are required. Spinners should be checked for proper operation on the surface, and should be run centralized. Multiple passes, both up and down should be made, and stationary readings should also be taken. Repeat runs are desirable to confirm stable flow conditions.|
Home | Tech & Tips | Production Logging |
The foregoing is an oversimplified discussion of the spinner log; most theoretical background and interpretative information has been omitted.