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Abstract Time lapse seismic survey (aka 4D seismic) is a geophysical tool used by the industry to guide and maximize field development. It has been proven successful mainly in clastic deposits environment (Gulf of Mexico, Gulf of Guinea, North sea,…) but sparsely tested on carbonate fields because of seismic quality concerns. Total E&P Qatar engaged in 2012 a "proof of concept" 4D pilot study on its operated Al Kahlij field - offshore Qatar- to demonstrate the value of information provided by a 4D seismic in a middle-east carbonate field under development. This study is made of: A feasibility study which aims to quantify the expected 4D effect by using a petro-elastic model and several chosen depletion scenarii. These input data are used to compute a synthetic time-lapse seismic dataset through a massive seismic modeling. A 4D pilot seismic survey shot in summer 2012 (monitor) which was designed to repeat the first seismic survey shot in 1998 (base). A dedicated seismic processing of both base and monitor in Total's 4D processing dedicated center followed by a specific inversion process (time warping) to extract the awaited 4D signal. The main objective on Al Khalij field is to validate that 4D seismic is able to calibrate the reservoir model and make it more predictive. If successful, the time-lapse seismic survey concept can be envisaged for other carbonates field in Qatar and in the Arabic Gulf area for field development optimization. Introduction The Al Khalij field is an oil producing field located in Block6, offshore Qatar (Figure 1). Total E&P Qatar has been developing the field with Qatar Petroleum since 1996. A 3D seismic survey was shot in 1998 and has been processed several times until 2009 to build the reservoir model used to monitor and further develop the field. The Al Khalij field is situated in transition zone, its water production rapidly increased to reach around 90% water-cut. Water arrival on the field is complex and implies several kinds of phenomena: short and long range injections, bottom and edge aquifer, large scale conductive events bringing water influx, etc. The field yields however large remaining reserves and it is planned to redevelop it. A better understanding of the water behavior is needed at a larger than well scale. Time-lapse seismic is a proven technique in clastic environments to assess fluid saturation changes both in time and space. Its efficiency in carbonate environments is still to be demonstrated in the Arabian gulf area. |
