Hafez, Karam Mohamed (Kuwait Oil Company) | Mukherjee, Pradip Kumar (Kuwait Oil company) | Anandan, Mudavakkat (Kuwait Oil Company) | Al-Ghareeb, Aisha (Kuwait Oil company) | Zahran, Wael Abdel Alim (Kuwait Oil Company) | Saleh, Tamer (Western Geco) | Cunnell, Chris (Western Geco)
Prestack depth migration (PSDM) can provide superior seismic volumes even in areas of low relief structures. A pilot PSDM study over the Greater Burgan oilfield in Kuwait demonstrated not only the uplift versus prestack time migration (PSTM), but also pointed to areas of further improvement in the velocity model building workflow. A full field (FF) study was subsequently performed, and incorporated the lessons learned from the pilot. The main area for enhancement was the integration of geological information into the velocity model. This included near-surface velocity characterization and incorporation of existing 3D log-based velocity models into the initial PSDM model, plus implicit geological constraints during the model updating workflow.
The results were a more geologically plausible velocity model with enhanced imaging versus both the legacy PSTM and pilot PSDM volumes, establishing the FF PSDM volume as the main seismic volume for interpretation, well planning and reservoir characterization for the Greater Burgan field.
The Greater Burgan oilfield is located in southeast Kuwait and is the main production field for Kuwait Oil Company (KOC), covering an area of approximately 850 km2. The geology is well documented (Carman, 1996), and is expressed as a broad, low relief anticlinal dome draped over a basement horst structure. The primary producing reservoirs are the Cretaceous-era Wara and Burgan sands (Figure 1), which are observed as a seismically quiet section with low acoustic impedance on the well logs. Deeper targets also exist in the Jurassic limestone reservoirs (e.g., Marrat).
A 3D seismic survey was acquired in 1997-98 covering an area of 1372 km2 using parameters commonly used at that time. This covered the complete Greater Burgan oilfield. Offset and azimuth distribution was mostly restricted to the inline direction (low aspect ratio survey geometry), which, in turn, imposes limitations on the utilization of full-azimuth information in the data processing and imaging sequence.
In 2010-11, a small test area was selected for a 3D PSDM pilot study. The aim of the pilot was to provide improved imaging compared to recent PSTM and a better input to ongoing horizontal and multilateral well programs. Particular attention was placed on enhancing the section between the primary reservoirs, the intra-reservoir clastic sequences, and imaging the minor faults that control compartmentalization. Key challenges included the near-surface complexity, characterized by rapid vertical and lateral velocity heterogeneity down to the Rus horizon (the shallowest mapped horizon in the field, between 200 and 500 m in depth, and consisting of high-velocity anhydrites), noise and multiple contamination of the legacy seismic data set, and reliable depth control of low relief structures across the pilot area.
Turkey, Laila (KOC) | Hafez, Karam Mohamed (KOC) | Vigier, Louise (Beicip) | Chimmalgi, Vishvanath Shivappa (Kuwait Oil Company) | Dashti, Hameeda Hussain (Kuwait Oil Company) | Datta, Kalyanbrata (KOC) | Knight, Roger (KOC) | Lefebvre, Christian (Beicip-Franlab) | Bond, Deryck John (Kuwait Oil Company) | Al-qattan, Abrar (KOC) | Al-Jadi, Manayer (Kuwait Oil Company) | De Medeiros, Maitre (Beicip) | Al-Kandari, Ibrahim (Kuwait Oil Company)
A pilot water flood was carried out in the Marrat reservoir in the Magwa Field. The main aim of this pilot was to allow an assessment of the ability to sustain injection, better understand reservoir characteristics. A sector model was built to help with this task.
An evaluation of the injectivity in Magwa Marrat reservoir was performed with particular attention to studying how injectivity varied as injected water quality was changed. This was done using modified Hall Plots, injection logs, flow logs and time lapse temperature logs.
Data acquisition during the course of the pilot was used to better understand reservoir heterogeneity. This included the acquisition of pressure transient and interference data, multiple production and injection logs, temperature logging, monitoring production water chemistry, the use of tracers and a re-evaluation of the log and core data to better understand to role of fractures.
A geological model using detailed reservoir characterization and a 3D discrete fracture network model was constructed. Fracture corridors were derived from fractured lineaments interpreted from different seismic attribute maps:
A sector model of the pilot flood area was then derived and used to integrate the results of the surveillance data. The main output is to develop an understanding of the natural fracture system occurring in the different units of the Marrat reservoir and to characterize their organization and distribution. The lessons learned from this sector modeling work will then be integrated in the Marrat full field study.
The work described here shows how pilot water flood results can be used to reduce risk related to both injectivity and to reservoir heterogeneity in the secondary development of a major reservoir.