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Dispersion in three-dimensional networks of polygonal fractures is determined by triangulating the network and solving the two-dimensional convection-diffusion equation in each fracture or by performing random walks. The general triangulation methodology and the numerical solution are summarized. The influence of the Péclet number, of the fracture density and of the fracture shape are systematically studied. Moreover, fracture networks are shown to belong to the same universality class as bond percolation networks.

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This paper introduces six new oil-water partitioning tracers suitable for use in oil reservoirs to estimate remaining oil saturation in inter-well regions. The tracers were tested in a field pilot in the Total-operated Lagrave field located in the South-West of France in 2011. The tests were successful for all six tracers.Measurement of remaining oil saturation in a near well region, using a single-well chemical tracer test (SWCTT) is commonly used in the oil industry. This method exploits the time lag of back-produced ester vs. hydrolysed alcohol. Partitioning inter-well tracer tests (PITTs), which can be used to assess inter-well oil saturation, are frequently used to investigate the presence and remediation of non-aqueous phase liquids (NAPLs) in aquifers. However PITTs are rare in the oil industry, with a few notable exceptions dating back to the 1990's. Consequently, few tracers are available for such tests in oil reservoirs. In addition, several of the tracers previously used were radio-labelled, which may restrict their application in many fields. Our main objective is therefore to expand the portfolio of environmentally acceptable partitioning tracers for PITT operations, and we present results from a field pilot where we successfully tested six new PITT tracers with oil-water partitioning coefficients ranging from 1.5 to 2.9.Lagrave is a relatively small carbonate field with fast injector-producer communications, which allows for relatively lowcost field qualification of partitioning tracers. Six partitioning tracers were injected in February 2011, together with a wellknown non-partitioning tracer (2-FBA). The pilot area encloses one injector and three producers. Frequent sampling (2-3 times per week) yielded concise tracer response curves well-suited for estimation of remaining oil saturation. The response curves from the partitioning tracers were compared to the non-partitioning tracer to estimate saturations. The results are also compared with other reservoir data.The class of new partitioning water tracers enables testing of oil saturation in inter-well regions and may become a vital tool to investigate the potential for enhanced oil recovery and assess the effect of EOR measures. Outside the oil industry, the new tracers should also be useful for NAPL identification and evaluation of NAPL remediation processes.

Tracer technology is an efficient and effective monitoring and surveillance tool with many useful applications in the oil and gas industry. Some of these applications include improving reservoir characterization, waterflood optimization, remaining oil saturation (Sor) determination, fluid pathways, and connectivity between wells. Tracer surveys can be deployed inter-well between an injector and offset producer(s) or as push-and-pull studies in a single well. Tracers can be classified several ways. (a) Based on their functionality: partitioning and passive tracers. Partitioning tracers interact with the reservoir and thus propagate slower than passive tracers do. The time lag between the two types can be used to estimate Sor, to ultimately assess and optimize EOR operations. (b) Based on their carrying fluid: water and gas tracers. These can be used in IOR or EOR operations. All gas tracers are partitioning tracers and the most common are perfluorocarbons; they are thermally stable, environmentally friendly, have high detectability and low natural occurrence in the reservoir. On the other hand, water tracers are passive tracers and the most commonly used ones are fluorinated acids. (c) Based on radioactivity: radioactive and non-radioactive tracers. Selecting a tracer to deploy in the field depends on a number of factors including their solubility, fluid compatibility, background concentration, stability, detectability, cost, and environmental impact. This paper provides an overview of various tracer applications in the oil and gas industry. These will include the single-well tracer test (SWCT), inter-well tracer test (IWTT), nano tracers, gas tracers and radioactive tracers. Their use will be highlighted in different scenarios. Field case studies will be reviewed for all types of tracers. Lessons learnt for all the applications, including what works and what does not work, will be shared. Specific cases and examples will include the optimization of waterflood operations, remaining oil saturation determination, flow paths and connectivity between wells, and IOR/EOR applications. The current state-of-the-art will be presented and novel emerging methods will be highlighted. This paper will showcase how the tracer technology has evolved over the years and how it shows great potential as a reservoir monitoring and surveillance tool.

Abstract. A three-dimensional fracture network in a granite block is reconstructed from a series of experimental serial sections. It is visualized and its most important geometrical characteristics are studied, namely the orientation of the fractures, the connectivity of the fractures, the number of cycles, per unit volume, the distributions of surface areas and of the intersection lengths, and the number of finite solid blocks isolated in the solid matrix by the network. Though the network mostly consists of two families of fractures, it is interesting to note that a simple model of randomly oriented, monodisperse hexagons often yields a good order of magnitude for the various geometrical properties, which have been measured on the real block. The flow properties are then studied; examples of velocity field are provided as well as histograms of velocities; the permeability tensor is determined and is found to be in good agreement with Snow's formula. Finally, dispersion is analyzed by means of a random walk method; histograms of arrival times are provided and interpreted in terms of dispersion tensor.

In EOR-operations, the single-well chemical tracer test (SWCTT) has been proven as a secure and stable methodology for measuring oil saturation prior to and after application of EOR-measures. SWCTTs can be used to measure residual oil saturation in a near-well region up to about 10 m from the wellbore, and has been used in several hundred studies, in particular in the US. Current simulation of SWCTT requires a reactive transport modelling tool that allows for a hydrolysis reaction involving four chemical compounds, in addition to other chemical tracers used in specific tests. Today compositional reservoir simulators are usually applied to simulate SWCTTs. In this paper we show that the SWCTT modelling can be made much simpler, without compromising a correct description of the reactive transport process. The formulation of the solution exploits the fundamental assumption that tracers do not affect the phase transport. A fast post-processing tracer simulation technique is introduced to solve single well tracer transport in real-life reservoir cases. The partitioning and reactions of the tracer components is solved fully coupled with the tracer transport, and partitioning between phases is described by a convenient formulation and the ester hydrolysis reaction is modelled in an efficient manner. The post-processing is based on previously solved reservoir simulation runs and gives significant savings in CPU-time. Using an experimental case and one field case, we demonstrate the practical improvement achieved by the new method, and investigate effects of numerical smearing. Our main conclusion is that the formulation is important to enhance correct evaluation of SWCTT results.