Case History Review of the Application of Pressure Transient Testing and Production Logging in Monitoring the Performance of the Mars Deepwater Gulf of Mexico Field

Abstract

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.

Statistical and numerical density derivatives: example of flow regime diagnosis and permeability k estimation

“…However, its accuracy depends on precise analysis and integrated reservoir studies. For over four decades, well testing has been transformed from a level mainly interested in determining a well's productivity to a sophisticated discipline capable of characterising the reservoir geometry, boundary and heterogeneity (Weiland 2008;Nnadi and Onyekonwu 2004;Freddy 2004;Kamal et al 2005;Jackson and Banerjee 2000;Landa et al 2000;Zakirov et al 2006). Pressure transient analysis (PTA) depends strongly on complex equations of fluid flow for a well flowing at a constant rate, and its analytical solution is limited to single-phase flow (Zheng 1997(Zheng , 2006 which in real case is never the situation due to well operational constraints and fluid mobility.…”

A new approach in pressure transient analysis part I: improved diagnosis of flow regimes in oil and gas wells

“…However, its accuracy depends on precise analysis and integrated reservoir studies. For over four decades, well testing has been transformed from a level mainly interested in determining a well's productivity to a sophisticated discipline capable of characterising the reservoir geometry, boundary and heterogeneity (Weiland, 2008;Nnadi and Onyekonwu, 2004;Freddy et al, 2004;Kamal et al, 2005;Jackson and Banerjee, 2000;Landa et al, 2000).…”

A New Approach in Pressure Transient Analysis Part I: Improved Diagnosis of Flow Regimes in Oil and Gas Wells

“…However its accuracy depends on precise analysis and integrated reservoir studies. For over 4 decades, welltesting has been transformed from a level mainly interested in determining a well's productivity to a sophisticated discipline capable of characterizing the reservoir geometry, boundary and heterogeneity [2][3][4][5][6][7][8].…”