Integration of Seismic Forward Modelling, Seismic Interpretation and Core and Log Analysis, Shuaiba Build-Up Area, Al Shaheen Field, Block 5 and Block 5 Extension, Offshore Qatar

Abstract

Abstract The Shuaiba reservoir of the Al Shaheen Field (Block 5 and Block 5 Extension, offshore Qatar) can be subdivided into a larger carbonate platform area located in the NE of Block 5 and an intra-platform basin (southern part of Block 5) that was filled in by a forced regressive wedge (FRW) system during the Upper Aptian regression. The FRW is characterized by clinoforms with a marly base that act as intraformational baffles or seals. Capturing these 3D geometries in detail, and specifically the exact location and nature of the platform-basin transition, is essential to developing the next generation geomodels for field development. Hence, an integrated study of core and log analysis, seismic forward modelling and seismic interpretation of a re-processed data cube was conducted. As a start, a field-wide correlation grid of available core and log data allowed for an initial coarse understanding of the depositional geometries and defined an approximate location of the platform-basin transition. As a second step, the expected depositional geometries were forward-modelled in order to better understand possible seismic responses within the bandwidth of the available 3D seismic survey. A complication is the relatively small thickness of the examined reservoir elements that are close to the limit of vertical seismic resolution. Finally, seismic interpretation picked up on this groundwork and it was possible to clearly map the platform margin, as well as the onset of the FRW in 3D. The obtained result was a detailed 3D seismic interpretation of the Shuaiba reservoir geometries, where the interpreted elements are tied with a grid of core and log interpretations. The key elements in the successful Shuaiba interpretation was early adaption of fully integrated and iterative geological and geophysical workflows where forward modelling of seismic responses was important for hypothesis testing. Introduction The Shuaiba Formation is amongst the most important reservoir units in the Middle East. Its layout on the SE Arabian Peninsula has been extensively studied over the years (e.g., Murris, 1980; van Buchem et al. 2002; Droste and Van Steenwinkel, 2004) and a regional sequence stratigraphic synthesis has been established by van Buchem et al. (2010). Yose et al. (2006; 2010) and Droste (2010) published seismic cross-sections from the U.A.E and Oman, respectively, which document the internal depositional geometries of the Shuaiba Formation in great detail. Capturing these 3D geometries, specifically the exact location and nature of the platform-basin transition, is essential for developing a robust structural framework as input to geomodelling. The Shuaiba Formation of Al Shaheen Field, Block 5 and Block 5 Extension, offshore Qatar, fits well into the regional sequence stratigraphic framework and thus comparable internal depositional geometries are to be expected. However, the interval in question is about 30% thinner than in many of the published examples (about 300 ft in Al Shaheen compared to 500 ft feet reported in the U.A.E.; Yose et al., 2006; 2010), which makes it difficult to interpret in the seismic realm. This is because the relevant stratigraphic building blocks are close to, or at the vertical resolution limit of the available 3D seismic data set. Seismic interpretation this close to the resolution limit calls for non-standard techniques. The focus of this paper is on documenting the integrated approach that was developed to successfully map the depositional geometries of the Shuaiba reservoir of Al Shaheen Field and presenting the resultant key outcomes.