Acquiring four-component seismic data with wideazimuth geometry provides an opportunity to build a very complete seismic picture for reservoir description. The recording of the full vector wavefield allows creation of both PS-wave data as well as P-wave images which contain different but complementary information. It also provides full-azimuth illumination of the subsurface. Azimuthal images improve definition of structural features, such as faults, that may only be illuminated within certain preferential shot-receiver azimuths. Differences in azimuthal images can also be very sensitive fault indicators in the case of small vertical displacements. Furthermore, and of crucial importance at the reservoir scale, wide-azimuth P-wave and PS-wave data lend themselves to the evaluation of azimuthal anisotropy. These attributes provide valuable spatial constraints in the characterization of heterogeneously distributed subseismic scale fractures.In 2003-04, Occidental Petroleum of Qatar, in partnership with Qatar Petroleum, acquired one of the first wideazimuth 4-C surveys in the Middle East, offshore Qatar which covered the Idd el Shargi "north dome" and "south dome" fields ( Figure 1). The reservoirs are within gentle anticlinal structures and have highly permeable fault zones and fracture corridors with small near-vertical displacements, which are often below the resolution of conventional narrow-azimuth streamer seismic. The reservoir now is undergoing secondary recovery with an extensive water-flooding program (Shifflet, 2003). For effective reservoir management, it is therefore of great importance to accurately detect the high-permeability zones for well placement and to increase the efficiency of injection programs.The ocean-bottom cable (OBC) data were acquired by Multiwave Geophysical using a patch geometry, with orthogonal receiver cable and shotline directions, providing full azimuthal coverage to offsets of 3000 m, equivalent to an offset/depth ratio of 2 for the main target zone. The nominal fold was 240 in the natural bin size of 9.4 ǂ 25 m. This gave sufficiently high signal/noise ratios, when used in conjunction with a more optimal bin size for imaging, to create eight azimuthlimited data sets for both the P and PS data. In total, one billion traces were acquired, making it one of the largest OBC surveys shot and processed to date. The main focus of the project was to apply an azimuth-friendly processing workflow (Gomez et al., 2004) to provide the optimum data preconditioning for a robust azimuthal anisotropy analysis following the methodology introduced by Angerer et al. (2003).In this paper, we present the main aspects of an integrated workflow comprising an adequate acquisition, specialized seismic processing, and robust attribute extraction for reservoir characterization. P-wave processing. The main objective of the study was the preservation of the azimuthal signal for subsequent anisotropy analysis. This had to be weighed against other objectives such as applying aggressive noise attenuation, or pu...

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Due to the complexity and cost of stimulating horizontal multilateral wells in an offshore environment, all aspects of this project type must be considered prior to project implementation. Utilizing all technical disciplines to understand the reservoir characteristics and select intervention candidates greatly influences the chance of success for any project. During 2006–2008, 39 wells (19 producers, 17 water injectors and 3 gas injectors) were stimulated in the Shuaiba reservoir in Idd El Shargi North Dome Field, offshore Qatar, resulting in production increases as high as 50% and injection increases as high as 100% in some wells. The wells were stimulated by rigless coiled tubing. A new tool that allows coiled tubing to enter each lateral in multilateral wells was used for these projects. This successful acid stimulation workover program utilized the fundamentals of engineering, geology, geophysics, and petrophysics and applied them with field operations. The screening methods developed led to further workover activity and new drilling development with anticipated reserve and production increases. Introduction Idd El Shargi North Dome (ISND) field was discovered in 1960. ISND is located approximately 55 miles east of Doha, Qatar. ISND is a shallow offshore field, located in water depths ranging between 100 and 150 feet (Fig 1). ISND production is dominated by the Jurassic Arab and Cretaceous Shuaiba carbonate formations, although Jurassic Uwainat (carbonate) and Cretaceous Nahr Umr (clastic) are also developed. Production began in 1964, and Occidental Petroleum of Qatar Ltd. (OPQL) entered into a production sharing agreement with the State of Qatar to operate and develop the field in 1994. The Shuaiba reservoir is the largest of the ISND reservoirs in terms of oil in place but the recovery factor is very low. The Shuaiba reservoir is a densely fractured and highly faulted, low permeability carbonate reservoir. Various well configurations such as single lateral horizontals and multilateral horizontal completions have been used to develop this reservoir. A liftboat unit was contracted in 2006 for data acquisition and rigless stimulation. The successful stimulation campaign explained in this paper is the result of utilizing all technical disciplines to understand the reservoir characteristics for selecting underperforming candidates and designing the stimulation. In this paper, an actual field example is used to show how candidate wells can be identified and how the intervention design can be prepared utilizing a multidisciplinary team effort (geophysicists, geologists, petrophysicists, reservoir and operations engineers). In addition, the paper will explain one technology that can be used to stimulate horizontal multilateral wells without a drilling/workover rig. The methodology described in this paper can be applied to any field that has horizontal and multilateral wells, especially those fields containing naturally fractured carbonate reservoirs. Reservoir Description The Shuaiba formation is extensively faulted and fractured due to domal uplift and regional tectonic events. Shuaiba is a high porosity and low permeability reservoir where large and small scale fracturing has created enhanced permeability regions and pathways in an otherwise tight matrix reservoir. The Shuaiba formation consists of four layers: Shuaiba A, B, C and D and is bounded by two shales: Nahr Umr (above) and Hawar (below). Shale barriers vertically separate the layers, although communication occurs through fractures and faults. Shuaiba A, B, and D are most productive and Shuaiba A is the most prolific, containing the highest percentage of the total Shuaiba oil in place. The Hawar Shale located below Shuaiba D closes the Shuaiba sequence. Immediately below the Hawar Shale is the Kharaib series of carbonate layers. These productive intervals are similar in nature to the Shuaiba D and are in pressure communication with the Shuaiba layers through fractures and faults.

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Summary Carbonate reservoirs are often very heterogeneous and their properties are frequently difficult to understand. The presence of faults and intense natural fractures further increases the complexity that becomes very challenging for reservoir management and field development. This is the case of the Shuaiba reservoir in Idd El Shargi North Dome (ISND) Field in offshore Qatar. The field was discovered in 1960 and was first produced in 1964. The oil is produced from multiple reservoirs, primarily carbonate, on a salt induced faulted anticline. After 1995, when Occidental Petroleum assumed the operatorship role under a Production Sharing Agreement with the State of Qatar, an extensive horizontal well drilling and waterflood campaign resulted in a substantial production increase from the primary Arab and Shuaiba reservoirs. This paper will focus on the Shuaiba development results. New technologies have been applied to effectively manage the Shuaiba waterflood and continuously increase the oil recovery factor in this complex reservoir. The practical aspects of multi-component seismic technology described in this paper can be applied in any complex fractured reservoir for improving efficiency and increasing recovery. During 2003–2005, Qatar Petroleum and Oxy acquired and processed a large 4C3D seismic survey over Idd El Shargi field (Fig.1). This technology uses multi-component phones and cross-spread acquisition geometry to record both compressional and shear (converted) waves. The survey ensured full azimuth coverage to offsets up to 3000 m, equivalent to an offset/depth ratio of two for the main target zone, achieving a nominal fold of 240 in the natural bin size, or a trace density of more than 2.7 million traces per square kilometer. The data were processed through a flow that carefully preserved the azimuthal anisotropy (Angerer et al, 2006).