Targeted tracer injection with online sensor
The invention is a method, a system, tools for use by the system, and an interpretation method for injecting and detecting tracers and conducting flow characterizing of a petroleum well. The method describes monitoring of travel time and slip velocity between two/three different phases (oil/water and possibly gas) in the well. The travel time and slip velocity are determined using an injection too for injection of an over pressurized injection of the partitioning tracers each of which would follow certain phase. The tracers are detected by an optical detection probe in the pipe. The slip velocity is obtained from the difference of travel time of two tracers which partition to two different phases.
1. A method of multi-phase petroleum well flow characterisation comprising,
for at least two injection positions, along the well, the well having a local production flow of target fluids water and hydrocarbon fluids (oil and/or gas) at each position, whereof
at least one or more zonal positions are along the production zone; and
a) for at least two of the positions;
using locally arranged injection devices;
injecting in a synchronized manner, at least one set of at least a water-affine and a hydrocarbon-affine tracer;
the tracers being optically detectable;
injecting the at least one set of tracer into and/or through all phases in the local production flow simultaneously allowing local mixing of the phases;
b) allowing transport of the production flow from the downhole injection points to a detector in the production flow at a detection point downstream of all the injection points;
c) at the detection point, determining arrival times of the tracers;
d) characterizing the flow behaviour of the well based on the arrival times of the tracers.
2. The method according to claim 1 , comprising calculating detection point slip times between corresponding arrival times of water- and hydrocarbon tracers as measured at the detection point;
back calculating detection point slip times to transport and local zonal slip times; and
characterizing the flow behaviour of the well based on the transport times and local zonal slip times.
3. A method according to claim 1 , wherein the characterization interpreting each zone into one or more flow regimes such as segregated, dispersed, annular and/or slug flow.
4. A method according to claim 1 , wherein before conducting step (a), establishing a stable flow regime in the well.
5. A method according to claim 1 , the tracers are luminescent or have specific light absorbing characteristics.
6. A method according to claim 1 , wherein the detection of the tracers are conducted using backscattered fluorescence measurements.
7. A method according to claim 1 , wherein during the optical measurement comprises
emitting light from a light source through an array of one or more windows arranged across the flow, into the flow, whereby the light generates tracer-specific back-scattered luminescence in the tracers present in the flow;
collecting the backscattered light entering (“returning”) through the array of windows, and calculating light intensity values of light representing the tracers; and
recording the light intensity values.
8. The method according to claim 1 , comprising defining arrival times of each detected tracer by defining a characteristic feature in a record/graph of the light intensity values.
9. The method according to claim 1 , comprising placing a reference injection at the location at or above the downstream end of the production zone to measure the transport times of the various phases to the online detection point further downstream.