The Najmah, Sargelu and Marrat are the main Jurassic reservoirs in Kuwait. These fractured carbonate reservoirs with moderate to low porosity were deposited in an inner to mid ramp warm marine environment. The fracture systems play a significant role in production from these reservoirs and it is imperative to identify areas of high fracture density. It has been observed that fractures associated with certain faults have facilitated the flow in the Jurassic reservoirs. Identification of faults and associated fractures has been mainly based on 3D/2D seismic data, image logs, cores and thin sections. A recent successful exploratory well in the Arifjan Prospect located on the eastern flank of the Greater Burgan Field, has opened up a large area which was previously considered to be nonproductive. There is excellent correlation between the fractures observed in cores, image logs and those predicted from the converted component of the zero-offset VSP. After registration of the z-component image with the converted image for various prominent reflectors, the discontinuities in the reflectors in the converted component image revealed fracture swarms which could be traced away from the well bore. This technique of processing the VSP data to identify fracture clusters could form a bridge between surface and borehole data and improve confidence in predicting fracture swarms away from the well bore in addition to assisting in planning for future surface seismic and 3D VSP surveys. Introduction The Arifjan prospect is located around 15 km east of the Greater Burgan field and lies along the Ahmadi ridge (Fig. 1). The area was considered to be non-prospective since a dry well was drilled in the year 2000 around 30 km to the north.The Ahmadi trend was re-interpreted and the reasons for the dry well were analyzed. Accordingly, an exploratory well was drilled during 2005 which showed excellent production from the fractured carbonate (Middle Marrat) formation which opened a large area for further appraisal drilling. In Kuwait, the Marrat formation is subdivided into Upper, Middle, and Lower members. Generally, the productive pay zones are limited to the 800' thick Middle Marrat, which is characterized by relatively clean limestone's with low gamma log character. By contrast, the Upper and Middle Marrat are more argillaceous and marly but are however reservoirs in some parts of north Kuwait. The overlying Najmah/Sargelu formation is composed of packstone and bituminous limestone deposited in outer-shelf depositional environment. The Arifjan prospect is covered with 240 fold 2D seismic data with a line spacing of around 2km. Using the available data, time and depth maps for all the major formations were produced. The relative fracture density for Marrat and Najmah reservoirs from geomechanical modeling studies based on the fault framework, were also generated to identify areas of better reservoir potential (Fig. 2). As part of the logging program, a zero-offset vertical seismic profile (ZVSP) was recorded utilizing a multi-level three component borehole seismic tool with a high peak force vibrator that provided superior signal fidelity with the consequence that the data quality was excellent even in zones with marginal cement behind the casing. Although the ZVSP was acquired for time-depth relationship and for correlation purposes, but special processing and analysis of the mode converted data indicated a strong correspondence with fractures identified in cores and image logs. While the processing of borehole data to obtain mode converted image is quite common in the industry, but this innovative method utilizes median velocity and F-K filtering using a 9 × 7 level sliding window in addition to special enhancement techniques on the ZVSP data to obtain superior images of the mode converted shear data. The registration process of the P-image with the mode converted image was achieved initially by the seismic time ratio attribute and subsequently by comparing events within a package to geological lithostratigraphic units. This new approach is expected to fill the gap between high resolution borehole image logs and relatively lower temporal resolution but higher spatial ZVSP data in predicting locales of better fracture clusters or swarms.

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Summary The Najmah, Sargelu, and Marrat reservoirs are the main Jurassic reservoirs in Kuwait. These fractured-carbonate reservoirs that have moderate-to-low porosity were deposited in an inner- to midramp warm marine environment. The fracture systems play a significant role in production in these reservoirs, and it is essential to identify areas of high fracture density. It has been observed that fractures associated with certain faults have facilitated the flow in the Jurassic reservoirs. Identification of faults and associated fractures mainly has been on the basis of 3D-/2D-seismic data, image logs, cores, and thin sections. The Greater Burgan field consists of the Burgan, Magwa, and Ahmadi structures. The four main reservoir units in the Greater Burgan field are the Wara, Mauddud, Burgan Third, and Burgan Fourth sands. The deeper reservoirs--namely, the Lower Cretaceous Ratawi and Minagish limestone--and the Jurassic Marrat formation contain significant oil reserves but are of less importance. However, a recent successful exploratory well in the Arifjan prospect, which is located on the eastern flank of the Greater Burgan field, has opened up a large area that was previously considered to be nonproductive. It has been noticed that there is excellent correlation between the fractures observed in cores and image logs and those predicted from the converted component of the zero-offset vertical seismic profile (VSP). After registration of the z-component image with the converted image for various prominent reflectors, the discontinuities in the reflectors in the converted-component image revealed fracture swarms that could be traced away from the wellbore. This technique of processing the VSP data to identify fracture clusters could form a bridge between surface and borehole data and improve confidence in predicting fracture swarms away from the wellbore and also assist in planning of future surface seismic and 3D VSP surveys.