Fiber-optic sensing technology has gradually become one of the pervasive tools in the monitoring and surveillance toolkit for reservoir and production engineers. Traditionally, sensing with fiber optic technology in the form of distributed temperature sensing (DTS) or distributed acoustic sensing (DAS), and most recently distributed strain sensing (DSS) and distributed chemical sensing (DCS), were done with the fiber being permanently clamped either behind the casing or production tubing. Clamping the fiber behind tubing or casing is sometimes beleaguered with operational challenges that often lead to rendering the fiber partially damaged or inoperable. The emergence of the composite carbon-rod (CR) system that can be easily deployed in and out of a well, similarly to wireline logging, has made it possible to sense any well without prior fiber-optic installation. In this paper, we present the lessons learned from the first well where we deployed in-well fiber-optic DAS/DTS. The DAS/DTS sensing was done in a few vertical oil producer wells and water injector wells without prior fiber-optic installation. The key objectives of the tests were to (1) investigate any well integrity across the entire length of each well, (2) assess production and injection flow profile across the perforations and behind casing, which hitherto was not possible with conventional production logging tool (PLT) tool, and (3) investigate the possibility of using the combination of distributed acoustic survey and distributed temperature survey for quantitative production flow analysis. This paper reviews the complete design and implementation of the in-well fiber-optic deployment, field operational issues, analyses, and interpretation of the sensing results. The combination of DAS/DTS data showed no well integrity related issues. The sensing data surprisingly pinpointed a few geological features such as cooling shallow aquifers that hitherto had not been noticed. The combination of different pulse widths during shut-in and production/injection cycles helped to refine the resolution of the flow profile from the production and injection zones.

The success of any improved oil recovery (IOR) project is largely dependent on how much oil is remaining to be mobilized within the targeted area of the partially depleted or mature reservoir. Partitioning tracers are generally used to measure residual oil saturation (Sor) or remaining oil saturation (ROS) in the near wellbore region via a single well chemical tracer test (SWCTT) or in an inter-well region via a partitioning inter-well tracer test (PITT). There is a limited repertoire of nonradioactive and environmentally friendly inter-well partitioning tracers for measuring ROS. A new class of environmentally friendly partitioning tracers was field tested, in a giant carbonate reservoir undergoing peripheral waterflood, for measuring ROS in inter-well regions in a depleted area. The new partitioning tracers were qualified via laboratory experiments and are deemed to be very stable at reservoir conditions (213°F and a salinity range of 60-200 kppm). The field pilot was conducted concurrently with a set of non-partitioning inter-well chemical tracer test (IWCTT) to determine reservoir connectivity, water breakthrough times, and injector-to-producer pair communication in an area selected for an IOR/EOR field pilot. An elaborate sampling and analysis program was carried out over a period of 30 months. This paper reviews the complete design and implementation of the test, operational issues, and the analyses and interpretation of the results. The breakthrough times of the passive and partitioning tracers are reported, and inter-well connectivity between the paired and cross-paired injectors and producers are analyzed. The ROS measured by a majority of the novel tracers is comparable to the saturations obtained via SWCTT, core and log derived saturations. The combination of conventional IWCTT and the novel partitioning tracers via PITT has been very useful in analyzing well interconnectivity, understanding the reservoir dynamics and quantifying remaining oil saturation distribution in the reservoir. This has led to better reservoir description and an improved dynamic simulation model.

SWCTTs are often used to assess residual oil saturation (Sor) or remaining oil saturation (ROS) in the near well-bore region before initiating enhanced oil recovery (EOR) or improved oil recovery (IOR) projects. The technique is based on the chromatographic separation of two different tracers. One oil/water partitioning tracer partly hydrolyzes in the reservoir, to generate a secondary non-partitioning water tracer. Most of the reported SWCTT operations typically use ethyl acetate (EtAc) as the primary tracer. Some of the challenges with the current set of chemicals used are their high flammability, poor detection limit (ppm range) and the large quantity required. A new set of tracers has been developed to overcome these challenges. These were pilot tested in a giant carbonate reservoir undergoing peripheral water-flood to measure Sor prior to a field redevelopment project. The new tracers were field tested concurrently with the conventional EtAc method for comparison purposes. About 100 g (0.1 kg) of each of the new tracers were injected at different times and different ways during the conventional SWCTT operation. It is worth highlighting that tens or hundreds of kilograms of conventional SWCTT tracer are needed for a single operation. This paper reviews the complete design and implementation of the test, operational issues, the analyses and the interpretation of the results. The Sor measured by each of the novel tracers compare well to that from a conventional SWCTT. The results also show that these tracers can be injected in pulse mode – at a very short time interval, thus reducing the operational time needed for pumping the chemicals. In addition, the test results suggest that several tracers with different partitioning coefficient may be deployed to investigate different depths of the reservoir. The pilot further demonstrate that many tracers with different properties may be deployed simultaneously without risking interference with the Sor measured during the test – this may revolutionize measurements of saturations in SWCTT operations.

Enhanced oil recovery (EOR) using CO2 is an important recovery process that can increase recoverable hydrocarbons and sequester CO2 simultaneously. For light oils, CO2 injection is particularly interesting and is considered a win-win strategy that sequesters CO2 and provides additional oil reserves at the same time. Saudi Aramco has designed and implemented the first CO2-EOR demonstration project in one of the fields. It is worth mentioning that while Saudi Aramco does not require EOR oil for decades to come, this project is being pursued primarily to demonstrate the feasibility of sequestering CO2 through EOR in the Kingdom and using it as grounds to test new monitoring and surveillance (M&S) techniques. The project consists of two components: the actual EOR project in a small part of a field, and the CO2 capture plant. An overall plan covering laboratory and research studies, reservoir modeling and simulation, monitoring and surveillance, construction of a CO2 capture facility, project implementation and evaluation will be presented for this first demonstration project. The project uses 40 million standard cubic feet per day (MMscf/d) of CO2 that is being captured and processed from an existing facility and piped about 85 km to the field location. An innovative progressive infill line drive has been implemented to take advantage of the east-west fluxes in the field. This includes a row of four injectors and four producers, and another set of observations wells for monitoring and surveillance. The CO2 is being injected in a water-alternating-gas (WAG) mode. An elaborate monitoring and surveillance program has been established and currently being implemented to evaluate the performance of the project. It includes the deployment of several new technologies including seismic, inter-well tracers, gravity, geochemical sampling and analyses that will be discussed in the paper. The main objectives of the demonstration project are estimation of sequestered CO2, determination of incremental oil recovery, addressing the risks and uncertainties involved, including migration of CO2 within the reservoir and operational concerns. It is estimated that up to ~40% of the injected CO2 will be sequestered permanently in the reservoir.