Best Practice and Case Study of Interwell Tracer Program Designs

Abstract

It is well known in the petroleum industry that tracer data can provide valuable information on reservoir characteristics and fluid flow performance. However, a prerequisite for obtaining reliable information is careful planning, design, and field implementation. The application of gas tracer technology for improving the reservoir description and optimizing the RKF Field miscible gas injection project was presented earlier. The current paper compliments the earlier work by discussing issues related to design and field implementation of the tracer program, including definition of the objectives, determination of tracer types and amounts, and evaluation of sampling and detection techniques. In this paper we document the lessons learned and propose best practices based on our experience with tracers in the RKF Field, Algeria. A critical element is integration of the field operator and Research Centre personnel with the subsurface team during all phases of the tracer program. This integration has been very important in obtaining good quality data in the RKF project. We also review common mistakes and bad practices that could occur in the absence of a robust tracer design program. The importance of analytical calculations, simulation, sampling frequency and the recycling of tracers are also among the design topics that are addressed. The proposed best practices can be applied by field operators in the design of future tracer projects and can also be used to identify the causes of tracer monitoring problems in existing projects. We hope that this paper will be of use to those managing or planning tracer projects. Introduction The Rhourde El Khrouf (RKF) Field is located in Block 406A of the Berkine Basin, 300-km southeast of Hassi Messaoud1. The field has been producing under partial pressure maintenance by miscible gas injection from the TAGI (Trias Argilo-Gréseux Inférieur) since 1996. Deeper volatile oil and retrograde gas condensate reservoirs provide makeup gas for the project. Tracer technology has been successfully applied in RKF. It is demonstrated that reliable tracer data can be obtained through careful planning, design, implementation, and monitoring. A key element of success is integration of the project team to include the disciplines of reservoir engineering, geosciences, field operations, and tracer specialists. This paper will discuss the integrated workflow and lessons learned, and will propose best practices based on the successful gas tracer project implemented in RKF field2. Background Tracer technology has been used for hydrocarbon reservoir characterization for more than 50 years3. Tracers can render information that is almost impossible to obtain with other methods, such as identifying flow paths, breakthrough times from injector to producers and estimations of the interwell oil saturation. Tracer technology is also used in the subsurface in single-well applications for mass balance calculations and saturation measurements. At the surface, tracers have been used in separator efficiency tests, and in transport lines and refinery surveys4,5. Tracer can provide very reliable information on fluid flow characteristics in secondary or tertiary recovery processes. Tracers reflect the reservoir dynamics and can be injected any time at the start of the injection or later to obtain the fluid flow paths and velocities in the reservoir. The type of tracer information acquired depends on the objectives for the application. Some objectives could include:detecting and documenting breakthrough times;mapping flow paths and performing analytical calculations; andmore advanced analyses using reservoir simulation to improve reservoir description and optimize reservoir management. Recent developments in tracer technology, especially in the areas of sampling and laboratory analysis techniques, have made it easier and less expensive to undertake a tracer project. This does not mean that it is not a complex procedure. On the contrary, based on our experience, a successful tracer project implies special technical, cost, and environmental considerations.

Practical methodology for interwell tracer applications

“…This integration looks to understand the fluid transport processes that occur in the porous medium. Based on experts criteria, the development of inter-well tracer tests can be divided into the following four stages [2][34]- [36]:…”

“…The sampling frequency should be established within the monitoring strategy according to the conditions identified in the injection pattern. The primary considerations to take into account are: monitoring the appropriate wells, not losing the tracer breakthrough, obtaining adequate profiles of produced tracer, making correct calculations of the volumes of produced tracer, and optimizing the cost of monitoring [36] [41]. In the literature, several sampling schemes proposed by different authors can be found, which in some cases are a function of the tracer breakthrough time [35]- [36], [41]- [46].…”

“…A critical element of tracer testing's success is the integration of all knowledge areas of the team, such as reservoir engineering, geosciences, field operations, and tracer technology specialists [36]. The scheme of the proposed methodology is presented in Figure 2.…”