Abstract

Tertiary waterfloods are an efficient and often economical method to increase reserves allocation and decrease Finding and Development costs. The use of Chemical Interwell Tracers (CIT) can be an excellent production enhancement tool for reservoir management. A CIT Program can be implemented at any time during the life of the flood to better understand fluid flow within a producing reservoir. Injecting chemical tracers into injection wells and catching water samples from producing wells offers an opportunity to determine, through direct fluid measurement, the differing fluid flow patterns in a reservoir. Tracers can determine what injected fluid is being produced at which producing well(s) in the field, but they do not allow for determining the actual flow path of the injected fluid. By integrating the chemical tracer results with the Coherence Cube ™, it is possible to determine the actual pathway of the fluid movement within the reservoir. This additional information can be extremely valuable in optimizing production and increasing the placement efficiency of injected water. This paper illustrates how combining the separate, proven technologies of Chemical Interwell Tracers and the Coherence Cube ™, can serve as an excellent reservoir management tool for well placement, production enhancement and cost reduction.

Introduction

This paper will endeavor to show, with mixed results, the potential value in combining two distinct and separate technologies to help in understanding preferential flow in reservoirs.

CHEMICAL INTERWELL TRACING - GENERAL DESCRIPTION

Interwell tracer programs have been used in water flood operations to confirm a field's directional heterogeneities and/or flow paths and barriers. This has been accomplished by combining practical field knowledge with reservoir simulation to develop the "Spectraflood" Design and Analysis System". The SpectraFlood program models fluid flow through porous media, potential heterogeneity sensitivity using the Dykstra-Parsons heterogeneity coefficient, and tracer inter-zonal mixing, using a stream tube model in this particular case. The SpectraFlood model allows for the determination of the chemical tracer concentration and quantity required, as well as the theoretical breakthrough times at each producing well. The breakthrough times are used to establish a sample collection schedule to make sure the "tracer wave(s)" is(are) not missed. This design process also takes into account project economics, environmental factors, and tracer detection limits. The tracer detection limits have a built-in safety factor in order to capture a wide range of potential variation in results. This is important in order to have faith in the data, because if chemical tracer(s) are not detected at some producing well(s), the question " Was there enough tracer added to be able to detect it?" could be asked. Therefore, with the built-in tracer volume injected, the answer is always, " if the tracer did not show up in the produced water samples at a producer, then fluid from that injector did not go there".

The family of chemical tracers was selected because they exhibited the following characteristics: [1]

  • Eighteen (18) potential tracers (one tracer per injection well) which can be detected with a single analysis;

  • Detectability at ultra-low concentrations of fifty (50) parts per trillion (ppt) under field conditions;

  • Nontoxic and environmentally safe;

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