The basic concept of IWTT is to inject a unique and stable chemical tracer that does not interact with the reservoir rock or oil into an injection well and monitor produced water from surrounding production wells. IWTT has been used for some time to understand fluid flow patterns in reservoir formations. With increasing interest in performing EOR (chemical or miscible CO2) in mature oil fields, information about the fluid flow is even more important due to the expense of chemicals/gas. IWTT can give information about:
- Reservoir barriers from faults or rock property changes like permeability. These barriers are identified by loss of tracer recovery or even a change in the time of tracer recovery.
- Identify limited gas saturated intervals that allow preferential water movement.
- Observe the difference in formation water from injection water.
- Estimate the reservoir volume or sweep that will result from EOR.
- Observe time for breakthrough to evaluate simulation models
- Document communication between injector wells that may result in sweep loss.
- Learn the residence time of the different water flow paths.
- Document the tracer recovery that is indicative of the injection distribution.
- Receive information about fingering between injector and producer from early tracer arrival.
Several types of compounds have been used from Inter Well Tracers. Radioactive isotopes, organic dyes, and substituted benzoic acids are the best known. CFT uses fluorinated benzoic acid compounds which have shown the long term stability, low oil phase solubility, resistance to biological reaction, range of compounds, and the low level detectability that has lead them to be a broadly used tracer. CFT does not use radioactive isotopes because of safety issues. Organic dyes have been used but have a limited stability over the lifetime of an Inter Well Tracer study and there are a limited number of dyes if the field is large and complex.
Chemical Flooding Technologies has developed analytical techniques working closely with Tracer Technologies International, Inc. (founded by Wallace Loder) which has been in the business of interwell tracing for years. Chemical Flooding Technologies will design the chemical tracer injection program, train field personnel in the collection of samples, analyze the samples, and assist the interpretation of the results. We have the ability to inject the water soluble salts at injection pressures up to 2,000 psi, and follow that with a sampling routine, analysis, and data interpretation to provide a complete service of Inter Well Tracer Testing.
Information typically required to design an IWTT include:
Net pay map of the pattern areas (including injector and producer well locations). From the map, we will need the legend to measure distances from injectors to producers.
Estimate of average porosity and formation net thickness
Injection rates. We prefer to have at least 4-weeks of continuous injection prior to starting the tracer injection (complete injection history is not required).
Production test for each producer (if available). We will be looking at pattern balance and understanding overall oil cuts (this is not essential).
Confirm that tracer work has not been previously performed on the field