TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractFor many of Asia Pacific low salinity medium to high porosity oil reservoirs, carbon-oxygen (C/O) logging has provided an effective method of through casing reservoir surveillance. This technology has been applied for well over two decades to provide saturation characterizations in conditions that are often challenging even in the openhole environment. To be successful, however, close attention must be paid to strict criteria during stages of problem identification, candidate review, well preparation, data acquisition, data processing and tool response interpretation.an input to reservoir description modeling • economic gains realized from recent C/O log applications This paper presents a short C/O technology overview, historical review of past practices, a review of joint discussions between team members providing and using the associated log application techniques and describes the ongoing Carbon-Oxygen Workshop Forum (COWF) review series. Additionally, some key C/O best practices developed from over 150 logging experiences in Indonesia are highlighted.

Proper characterization of a producing well has significant impact on asset management. Production schedules from different wells and further infill drilling in a field depend on the effectiveness and the pattern of the production drive mechanism. Whether the reservoir displays partial aquifer influx or is waterflooded, the flow profile of produced/injected water as well as the reservoir pressure, permeability, fluid saturations, and formation compaction are useful to properly evaluate the overall sweep efficiency. This information is more crucial in a field with multi-layered reservoirs having different permeability, pressures, and structure. Data acquisition should be scheduled and compared to baseline data such as a baseline pulsed neutron capture, production, or compaction logs. There should also be plans to monitor specific wells over the life of the project to observe and optimize the reservoir performance, characterize the reservoir response, and in the case of waterflooded reservoirs monitor the performance of the waterflood. Multi-rate multi-zone production logging and pressure transient testing are two excellent methods to achieve these goals. Introduction Production in Mars field in the Gulf of Mexico began in 1996 and peaked in June of 2000 at 208,000 B/D of oil and 217 MMscf/D of gas. The deepwater Mars field is a prime candidate for secondary recovery since the predicted primary recovery has limited aquifer support. Monitoring the waterflood with cased hole logs is critical to improving the performance and increasing the overall volume recovery of the Mars field. The ability to acquire carbon oxygen data for monitoring sea water injection and sigma data for reservoir fluid changes, combined with multi-rate production logging and testing is essential in reducing unnecessary risks of well intervention. Many of the Mars wells produce from multiple reservoir layers so multi-rate production logging and well testing surveys are valuable methods to estimate the layer flowrates, pressures, permeabilities, skin factor of individual layers, and distance to and type of boundaries. A surveillance logging program has been conducted in the Mississippi Canyon Block 807 area since 2004 with initial baseline surveys to monitor and to optimize the production performance of the field and to inspect the waterflood progress. This approach allows reservoir characterization without requiring zonal isolation. It also helps to evaluate where the waterflood has influenced pressure maintenance. The results of the multi-rate multi-zone (MRMZ) production logging and testing combined with saturation trends confirm and provide valuable data for the reservoir modeling. Another benefit of the step-rate production testing is the evaluation of the layer contribution to the total production. This data together with estimated individual reservoir layer pressures helps to determine oil reserves and assist in waterflood management. The data acquisition for these wells is being conducted in realtime to optimize the stabilization times for each test period. Thus, the required data is being acquired without recording unnecessary information or conversely, not obtaining sufficient data. The combined pressure transient testing and the MRMZ production logging of several of the wells tested in the Mars field will be described in detail to illustrate the monitoring technique and to show the time-lapse changes occurring in the Mars field. The flow pattern of the produced water, the reservoir sweep, the reservoir pressure profile, permeability, skin damage, and fluid saturations will be provided and discussed in detail to highlight the results of the time-lapse monitoring of the reservoir. Both the waterflooded and the non-waterflooded case studies will be discussed. While pulsed neutron capture and formation compaction logs are mentioned as surveillance tools, they are not discussed in detail.

Evaluation of cement bonding and zonal isolation is a challenge that the oil and gas industry continues to face as wells are drilled deeper within more hostile environments. The complexity of this task has increased as these wellbores have more challenging trajectories and being drilled in formations for which there is little drilling and completions experience. In addition, cement slurries have become more complex with the addition of inert gases, micro-spheres, non-traditional liquids, and many other additives designed to improve the cement sheath quality. These slurries require non-traditional interpretation methods to effectively evaluate the cement sheath because older methods do not yield accurate results in these situations. This paper will present information concerning the existing cement evaluation logging tools, basic interpretation techniques, and an overview of the new, advanced methods for existing tools available from a variety of vendors in the industry. Progress is continuously being made in the development of more effective cement evaluation tools and evaluation techniques. Standard cement evaluation logging tools consists of two major classes, sonic and ultrasonic. The standard cement bond log, segmented bond log, and radial bond log are all part of the sonic logging family. The ultrasonic family consists of tools with either a rotating transducer or a stationary array of transducers. This paper, however, will not focus on the hardware but will focus on the interpretation of available measurements and on facilitating optimized decisions using measurements from both families. Advanced interpretation methods discussed in this paper broaden and refine previously published methods in order to effectively evaluate wellbore conditions with the commonly available cement evaluation tools. The original processes developed in the early 1990s now incorporate a statistical variance mapping display for both the sonic and ultrasonic tools. The resulting variance image from the ultrasonic tools allows detection of minor changes in cement or fluid composition and aids in the interpretation of the pipe-to-cement bond. This technique provides a robust answer product helpful in diagnosing zonal isolation and highlighting channeling and quality of materials behind pipe for all cement compositions. It is also possible today to process and interpret non-standard sonic data, such as refracted monopole and flexural dipole from logging tools not specifically designed for cement evaluation. Correct application of the newer interpretation techniques described in this paper can lead to fully evaluated cement sheath quality and distribution behind pipe. Several examples using the new advanced interpretation methods will be presented including comparisons (1) between a scanning ultrasonic tool and a radial bond tool (2) a sequence of evaluations using a cement bond log combined with an ultrasonic tool before and after several multiple remedial squeeze operations, and (3) also a comparison between two different scanning ultrasonic tools and a segmented bond tool. The final example shows a successful use of the new technique in a completion using titanium casing. Basic Cement Evaluation Tools There are two major classes of standard cement evaluation logging tools (or logs), sonic and ultrasonic. The sonic logs include cement bond (CBL), segmented bond (SB), and the radial bond (RB). The ultrasonic logs consist of two types of tools, one having a rotating transducer and the other has eight stationary transducers. Several previously published papers in the bibliography Frisch et al.[1,3,4] provide more detail about tool theory and applications.

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