Introduction The labeling of the injection water with a radioactive or chemical tracer has been applied successfully to establish interwell flow patterns in waterfloods and EOR projects. Samples taken from the production wells surrounding the injector are analyzed quantitatively for the presence of tracer. Information about preferential flow and lateral sweep can be obtained. Most reservoirs exhibit stratification, with different sands having different flow properties. This will result in different breakthrough times properties. This will result in different breakthrough times for the injected water in the producing wells. Since the tracer concentration of the sample taken periodically from the well represents an average value, there is, in general, no possibility to indicate the layer(s) from which the tracer originates. The subsurface flood performance can be determined in situ if an observation well is drilled at a suitable location between the injector and the producer. The injection water is labeled with a radionuclide that emits gamma rays powerful enough to be detected through the casing (e.g., powerful enough to be detected through the casing (e.g., cobalt-60). With a conventional gamma ray logging tool the tagged injection water can be detected by comparing the log periodically run after the injection with the base log (before injection). The development of vertical sweep around the wellbore can be established. Thief zones and zones unaffected by the flood can be identified. Tracer Selection and Well Logging Response Any tracer that is to be used in this technique for indicating the vertical sweep has to meet certain general requirements.Losses because of adsorption in the formation rock must not occur. Very positive results were obtained with the application of cobalt hexacyanides in several field tests. These tracers show no tendency to get adsorbed and are stable under most reservoir conditions.To produce a clear, unambiguous response on a logging tool in a nonproducing observation well, the radio-nuclide used should emit gamma rays powerful enough to be detected through the casing.The radioactive lifetime (as indicated by the half-life) of the tracer should be at least of the same time scale as the project. Table 1 lists a number of potentially suitable nuclides, their half-lives, yield, and energy of principal gamma rays. The properties of naturally occurring potassium-40 are included in the table as reference. potassium-40 are included in the table as reference. The total amount of a radioactive tracer to be injected to produce a detectable signal on the logs is determined, in principle, by two factors:the tracer concentration Co in the surroundings of the observation wellbore, which causes a signal of sufficient intensity to be detected above the background in the particular formation, andthe total volume, V, in which the tracer is diluted. In practice, both the upper limits for Co and the total activity practice, both the upper limits for Co and the total activity to be injected, Co x V, often are dictated by standards of radiological safety. Especially in those experiments where a producing well is used for sampling purposes, the design of a test must guarantee that the radioactivity levels in the produced water will not exceed standards for water as currently recommended by the Intl. Commission on Radiological Protection (ICRP). A simple relation between the signal from the detector and a given concentration of a nuclide in the formation around the detector is: (1) where Co = activity per unit volume of the formation, Bq/m [curie/cu ft],= linear attenuation coefficient in theformation for the photons emitted by thenuclide, m [ft ], and= constant representing detector propertiesand physical properties of the nuclide, m [sq ft]. JPT p. 711

Summary Partitioning tracer tests are used to determine residual oil saturation (ROS). At Koninklijke/Shell Laboratorium, Amsterdam, laboratory equipment based on the flow injection analysis (FIA) method has been constructed for rapid (within 2 hours) and accurate (better than 8%) determination of the equilibrium partition coefficient of tracers between crude oil and brine under simulated reservoir conditions. The apparatus makes possible investigation of the influence of all relevant parameters on the partition coefficient: tracer type and concentration, crude oil type, pressure (up to 34 MPa [4,930 psi]), GOR'S, temperature (up to 150 deg. C [302 deg. F]), and brine psi]), GOR'S, temperature (up to 150 deg. C [302 deg. F]), and brine salinity. The FIA equipment has been critically evaluated with model compounds. Its versatility has been verified with experimental results obtained on dead and live crudes. Introduction Economic incentives for optimizing reservoir production have focused attention on the development of methods to obtain information on the internal structure and associated fluid saturations of the reservoir. The application of tracers, in combination with advanced reservoir analysis techniques, provides a successful method of generating this information at every stage (waterdrive and tertiary recovery) of the reservoir development without costly interruption of normal operations. In a special application of tracer techniques, partitioning of the tracer between the different liquids present in partitioning of the tracer between the different liquids present in the formation can be used to obtain information on the reservoir. In particular, equilibrium partitioning of a tracer between the oil and aqueous brine phases may yield information on the amount of residual oil present in the watered-out reservoir. In the interwell tracer test (IWTT), a solution of partitioning tracer is pumped downhole, displaced with the brine, and detected by sampling a producing well. The tracer zone migrates in the reservoir at a velocity less than that of the brine because the tracer molecules dissolve partially into the stationary phase. The retardation of the tracer zone is directly connected with the amount of oil present; i.e., measurement of the residence time yields the required present; i.e., measurement of the residence time yields the required information on the ROS, Sor, as given by (1) where the partition coefficient K= C /C, C and C, =concentrations at equilibrium of the tracer in oil and water phases, and = retardation or capacity factor given by the ratio of the amounts of tracer in the oil and brine phases. In practice, can be obtained experimentally as the relative differ-ence in residence times in the reservoir for the retarded partitioning tracer, t, and a nonpartitioning tracer, t, flowing along partitioning tracer, t, and a nonpartitioning tracer, t, flowing along the same paths: (2) It can be seen from Eq. 1 that accurate determination of the partition coefficient, K, of the tracers involved in the tests is a keep partition coefficient, K, of the tracers involved in the tests is a keep step for accurate determination of ROS in watered-out reservoirs. K-Value Determination A useful source of K values obtained by manual procedures in model solvent/water systems is Ref. 4. Data on real crude/brine systems are scarce. A well-known method for determining the K value is the shake-flask technique, in which oil and brine are brought into contact by mechanical shaking and stirring. The technique is not very suitable, however, because equilibrium is reached only after several days and oil and brine are less likely to form (stable) emulsions. In the dynamic method applied to evaluate the popular singlewell tracer test (SWTT), brine with a known initial concentration of tracer is continuously circulated through a cell filled with oil until equilibrium is established. Reliable K values can be obtained within a reasonable time. At the relatively high concentration of chemical tracers applied in the SWTT, the partition coefficient is dependent on the concentration. The K-value/concentration relation is measured beforehand and incorporated into the interpretation of the SWTT. To circumvent this complicating factor, the partition tracer test should be carried out at a very low tracer concentration (e.g., with radioactively labeled compounds) where is no longer concentration dependent. To extend the measurements of K values to very low tracer concentrations, we selected FIA as the instrumental approach. Witthe FIA apparatus described, all relevant parameters influencing the partition coefficient in either dead or live crude oil systems can be readily investigated, as shown in this paper.

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To ensure that ergonomics are taken into account in the conceptual design phases of engineering projects, NAM has introduced the 'Ergonomics in design' workshop. This paper describes the general format, timing and techniques used in these workshops. An example of a case study is presented together with a cost benefit analysis. Finally, a concluding summary of the workshop success factors is given together with the areas for further improvement. Introduction The NAM company is engaged in the exploration for and production of oil and gas in the Netherlands and in the Dutch sector of the Continental Shelf. In 1995 its total gas production was 57 billion m3 and 1.9 million m3 oil. The design of equipment and production systems is a key factor in efficient and safe working. People today expect their equipment to be designed for easy use, and international Regulations call increasingly for safe and healthy workplaces. These demands place high responsibilities on those who design working equipment and production systems: they can be legally called to account if people are injured or develop occupational diseases; their companies will lose business if the competitor's equipment is more efficient and safer in use (Corlett and Clark, 1995). This paper is of particular interest to those concerned with the design, engineering, operation and management of production systems in the oil and gas industry. Designing technology that accommodates the capabilities, constraints and needs of the human user (operator) is the concern of 'ergonomics'. The term ergonomics is prevalent all over the world, except in the USA and a few other countries, were the term 'human factors' is more prevalent. Our company has adopted the following definition of ergonomics: 'A multidisciplinary field of science, and its application, which considers the integrated knowledge of human capabilities, limitations and needs in the interaction between humans, technology and the working environment for the design of work systems, workplaces and products'. The company has an integrated Health, Safety & Environment (HSE) organisation including ergonomics/human factors expertise. In line with the Shell Groups' Human Factors Engineering Strategy, the company pursues four objectives for the design of equipment and production systems. These ergonomic objectives and definitions are presented in table 1. Most of the objectives presented in table 1 have a special focus on human-machine interaction and the associated benefits apply both to the users and the performance of production systems. Integrity, as defined in table 1, is not the private domain of ergonomics. It overlaps the domain of other occupational health and safety disciplines. The added value however, is that ergonomics prevents health and safety hazards at the source, especially at the interface 'human-machine'. This pro-active approach also applies to system improvements in terms of reliability, efficiency and usability. To meet these objectives in, for example, the design of a drill cabin for a drilling rig, the cabin should provide easy access, sufficient drillfloor overview and protection against hazards, such as noise, vibration, mechanical impact and severe weather conditions. Type and layout of chair(s), operating console, displays and controls should accommodate drillers physical and cognitive capabilities, constraints and needs to prevent musculo-skeletal strain, discomfort, mental stress and operating errors and its associated consequences. It is of vital importance that designs do not only respond to the physical properties and constraints of the users, but respond also to their cognitive (information processing) capabilities in order to prevent human errors and thus enhance reliability of the operations. P. 297