Processing and Preliminary Interpretation of the Ultra High-Density Full-Azimuth 3D Seismic Survey, Dukhan Field, Qatar

Abstract

Abstract The Dukhan Field 3D seismic survey is an ultra high-density wide azimuth survey (i.e., point source and receiver, short source and receiver line interval, and full azimuth recording) intended to provide a significant uplift in quality and resolution to enable the imaging of reservoir sub-layers and fine-scale structural features. This paper presents the challenges and lessons learned from full-field processing and inversion. Seismic interpretation demonstrates added value to the field, which leads to improved reservoir models and support to well operations through improved well placement. Subtle structural, stratigraphic, and diagenetic features are now imaged. Knowledge gained from processing this survey includes:cost, time, and effort invested on the Dukhan 3D survey is worthwhile as high quality results are obtained at 15m bin processing;3.75m bin processing is now possible, and could be performed to improve image quality over the full seismic bandwidth for all reservoir intervals;Pre-Stack Depth Migration (PSDM) workflow is recommended for optimal offset and azimuth reconciliation and noise attenuation;the adverse effect of near-surface geologic variability on seismic data quality can be improved by utilizing microgravity and resistivity (Vertical Electrical Sounding) techniques; andproper preconditioning of the input data is critical for reliable prediction of reservoir properties away from well control. While industry's knowledge and experience in acquisition and field operation of ultra high-density full-azimuth seismic has increased over the last 3 years, processing of such data to ensure optimal imaging and reliable reservoir property predictions (e.g., porosity) has lagged. QP believes that lessons learned through this round of processing can provide insight for prediction of rock properties in the major Dukhan reservoirs. Introduction The Dukhan field is located along the south west coast of Qatar, extending 70 kilometers north-south (Figure 1) and is one of three giant oil and gas fields in which Qatar Petroleum (QP) retains 100% interest. It was discovered in 1939 and has produced from three oil reservoirs (Arab-C, Arab-D, Uwainat) and one gas reservoir (Khuff). It is the only onshore field in Qatar and more than 750 wells have been drilled to date. Over the past 70 years, the hydrocarbon development and production history at Dukhan has undergone several phases. Initially, the oil and gas reservoirs were produced using natural pressure depletion. Water injection was started in the mid to late 1960's as pressures begin to fall. A more efficient power water injection system and horizontal well technology were introduced in the late 80's.