Introduction to Tracer Injection
Tracers are used in the oil industry in order to qualitatively or quantitatively gauge how fluid flows through the reservoir. The technique has been applied in numerous fields throughout the world. In interwell tests, mixture of water and suitable tracer (which is compatible and non-reactive with reservoir rock and fluid and “foreign” to the system) is injected at the wellhead and its presence in the aqueous phase at potential target producing wells throughout the field is monitored. Analysis of the resulting tracer concentration versus time curves from individual producing wells enables interwell flow characteristics to be determined so that improvements can be made to increase injection fluid sweep efficiency of the hydrocarbon reserve.
This document sets out the technical and practical requirements for a tracer investigation to establish injected water breakthrough and tracer concentration versus time information from two water injection wells to a target producer(s) in the Balal field.
Tracer studies can provide the following information:
- Fault/barrier communication testing.
- Determination of source of produced water at all target production wells from the injection well.
- Simulator Models modification based on tracer breakthrough time.
- Determination of each injector share in producing water in specific production well.
- Volumetric sweep efficiency estimation using average tracer transit time from each injector to producer wells.
Background information on waterflood tracer technology:
As part of reservoir injection water monitoring programs, tracer can be introduced into the injection water, in order that interwell flow patterns may be established.
In the case of chemical tracer use, the material is a compound that is stable at reservoir conditions and not present (or present in known concentration) in reservoir connate water, formation or injection seawater in order that it can be unequally detected at producing wells.
Information generated from waterflood tracer surveys
Tracers have been used successfully on many occasions to determine flow characteristics of injection water reservoir systems throughout the world. The data from these projects has been used to monitor and assess many flow parameters. Although computer simulation models of reservoir systems, developed using data generated during reservoir seismic surveys, pressure measurements and wellbore logging can give an indication of expected injection fluid flow through a reservoir system, they can not be completely relied upon to give accurate information on actual flow.
Primarily, this is due to the scale of oil reservoir operations where normally wells are hundreds of meters apart enabling unknown interwell formation heterogeneity’s to occur (e.g. high permeability streaks, interzone communications).
In waterflood applications, tracers have been useful in the refinement of computer modelling of reservoir systems through determination of breakthrough times, injector and producer relationships, interzone communication, thief zones and channeling. Additionally, by using this technique, information has been obtained on the flow of polymer thickening agents between wells and the effectiveness of polymer blocking operations in high permeability streak wells. The addition of tracer at the waterflood front enables the detection of first seawater breakthrough to be determined in order that effective scale inhibition programs may be implemented.