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TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractThis paper presents results related to the use of the ball sealer diversion technique to fracture long and multiple Triassic sand intervals in the Alwyn Field. It also focuses on the methodology adopted to design and prepare the treatment. This technique was applied on a well producing from a gross pay zone thickness of 350 m with a perforated length of 98 meters. The production decreased drastically after condensate deposition in all reservoir intervals induced high skin levels. Due to low permeability, matrix treatments were discarded as a solution. Instead, a proppant fracture treatment was planned to by-pass the skin, using ball sealer diversion to treat the entire perforated interval.The treatment was performed successfully in several stages including gel pad, proppant and ball sealers. Good indications of diversion showed that most of the intervals were fractured. However, performing such a treatment requires sophisticated engineering to determine the optimum number of stages, number of ball sealers per stage, gel and proppant volumes per stage and pumping rate. The success of this operation will allow the technique to be considered for wider application such as fracturing long intervals in deviated or horizontal perforated wells at moderate cost.

Building on the successful acidification of long cemented and perforated drains (~1000m) during the Central Area Development Phase of its AlKhalij Offshore field in Qatar (refer to SPE 54739), TotalFinaElf faced a new challenge for upcoming South-East Area Development Phase: how to boost productivity in extra-long drains applying previously proven principles, without going through unaffordable rig time? To snatch the maximum productivity (highest Productivity Index - PI) from horizontal drains in the over 2000m range, an homogeneous participation to production of the perforated intervals throughout the drain is crucial. In the matrix Mishrift carbonated horizon, a successful acid job is the key to meet the high production expectations that such long drains promised. The success of the stimulation relies on the necessity to open first the "toe" of the drain prior to bull heading - through a DST string - emulsified acid and water soluble balls sealers as the diverting agent. To deal with the here above requirements and in a "Rig time saving" approach, the "toe" and the remaining zones (the "heel") were successively perforated in one TCP run while ensuring pre-acidification of the lowermost perforations. The "double trigger" perforation technique was designed by the TotalFinaElf team in collaboration with the Service supplier. This technique consists in shooting the lower perforations in acid, squeeze this "in place" acid through annulus at a high pumping rate (to ensure a good Injectivity Index at the toe) and trigger the remaining perforations (remaining production intervals) in the same TCP run. Once TCP are pulled out of hole, a DST / acid string is run in hole and the main acid job performed in bull heading. The reservoir being hydrostatic to sub-hydrostatic, the well is kept on losses while running final completion. This paper documents the engineering approach and operational methodology implemented to reach high efficiency targets. Case histories are presented to illustrate these procedures, treatment designs and productivity results. Introduction The AlKhalij field. AlKhalij is an oil field located in the northern part of the Qatar sector of the Arabian Gulf. The Mishrift Reservoir. The reservoir is a stratigraphic trap. The oil bearing reservoir is part of the Mishrift formation within the Cenomanian limestones. The reservoir consists of a vertical succession of 6–9m (20–30ft) shallowing-up sequences. Each of them containing an alternance of poor permeability matricial layers and highly productive "drains" which can be correlated at the scale of the field. The total thickness of the Mishrift formation can reach 150m 500ft).

The Khuff Formation is a major reservoir in Qatar and the rest of the Middle East Gulf region, and contains some of the world's biggest gas reserves. Geologically the carbonate platform system is complex with fine-scale heterogeneities which impact the static and dynamic reservoir characteristics. These heterogeneities are depositional, stratigraphic and diagenetic in nature and therefore reservoir characterization needs to be an integrated multidisciplinary and multiscale approach. In order to address these issues a large multidisciplinary and multiscale subsurface study has been launched on a large database including fields from across the region. The aim is to better understand the facies distributions, sequence stratigraphic architecture and the regional reservoir development, in order to better characterize dynamically reservoir behavior.