TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractHydraulic fracturing using proppants is a well established technique for increasing well productivity.However, uncontrolled mineral scale deposition within the proppant pack can result in reduced conductivity and fracture performance, thereby devaluing the initial investment in the fracture. To protect this investment an active scale control strategy is required especially when executed in the presence of a water flood. A number of different techniques have been proposed and used historically, however they have all suffered with one or more drawbacks. These drawbacks have included excessive volumes, poor placement control, short treatment life and / or the potential for fines and sand generation and pack instability. The ability to place scale inhibitor within the voids of a porous proppant offers a robust technique for placing a large amount of scale inhibitor throughout the proppant pack while its controlled released protects the productivity of the fracture.Previous papers have described the development of porous, scale inhibitor impregnated proppants and highlighted the initial returns from field trials performed on land wells on the North Slope of Alaska. The impregnated proppant technology has now been further developed and two treatments have recently been deployed in the North Sea. The treatments were both designed to stimulate production and to protect the fracture against future scaling scenarios. This paper will describe the design criteria used to select this method of protecting the future performance of the fracture. In addition this paper will describe the design and execution of the treatments while highlighting the fracture performance and scale inhibitor return profiles generated by recent treatments performed in the British and Norwegian sectors of the North Sea.

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With an initial reservoir pressure of 911bar and a downhole temperature of 170 o C Kristin is the first HPHT field in the world that has been completed and produced using subsea solutions. CaCO 3 scale has been identified as the major production problem due to the expected high draw down from the reservoir together with the high level of bicarbonate and calcium in the formation water. In April 2007 breakthrough of formation water in two of the wells were detected and the subsurface safety valve in one of them showed increasing inertia. In August/September 2007 the first combined scale dissolver & squeeze treatments were carried out in these two wells. This culminated after more than 5 years of testing of a large variety of chemicals and operational planning. The jobs were successfully carried out using the unique HP injection system on board that is dedicated for such well intervention. In this paper a full case history of these first treatments on Kristin will be presented. It starts with a brief summary of the difficult path to qualify various chemicals for the challenging conditions. This is followed by the early detection, diagnosis and data interpretation processes when the formation water first broke through. The paper will include the operational planning with special focus on the constraints to inject chemicals at an adequate rate against a HPHT well. The challenges in delivering and maintaining separation of the different chemical pills to a well lying 7km away will be highlighted. Despite the best intension some compromises on the treatment design have to be made in order to maintain safety and system integrity and these will be discussed. Finally the paper will conclude by presenting the results from these treatments, the assessment of the operations, the experiences being learnt and the area identified for future improvement.

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractAqueous based scale inhibitor squeeze treatments have been routinely deployed on Total Oil Marine's North Alwyn field for many years. More recently, declining reservoir pressure in parts of the field, coupled to poor reservoir communication has led to a considerable increase in the time required to bring treated wells back onto production. On subsea well 3/4a-15s, it was anticipated that extended shut-in periods would be required to allow sufficient pressure build up for production restart following a platform squeeze.To minimise deferred oil cost associated with scale inhibitor treatments an alternative deployment technique has been applied to treat subsea wells such as 3/4a-15s on North Alwyn.A weighted solid scale inhibitor capsule, suspended in a carrier brine has been pumped to the wellhead and allowed to fall, under gravity into the sump. On reaching the sump, the diffusion of scale inhibitor from the capsule established a concentration gradient, which delivered a near constant level of inhibitor over the lifetime of the treatment.The subsea well on North Alwyn treated using this technique returned to production in less than 24 hours. In addition, the encapsulated inhibitor treatments have out-performed previous squeeze treatments, protecting a large volume of water to the minimum inhibitor concentration (MIC). This paper will describe the concept of the delivery system, details of the treatments and present the return profiles.

Inhibitor squeeze treatments have been regularly carried out to prevent both sulphate and carbonate scale depositions from reservoir to topside facilities in North Sea field since 1990s. Some of the wells, especially for the short perforation, high water production wells and relatively clean sandstone with little amount of clay material, had experienced a relatively short squeeze life with traditional squeeze treatment.In this paper, an oilfield scale technology toolbox has been introduced to meet the challenge of squeeze treatment for high water production and short perforation ESP well, including scale inhibitor molecular design, squeeze life enhancement technique, squeeze design, inhibitor residual analysis technique, application and deployment techniques. Field trials were carried out with a satisfactory result. This paper outlines the idea of how a special monomer was introduced into a polymer to provide improved inhibition performance and enhanced adsorption and retention capability, along with squeeze life enhancement technique through crosslinking and bridging capability with other ionic polymer additives. In addition, the squeeze life enhancement techniques through squeeze treatment design, residual analysis and deployment are discussed. A detailed lab test program to qualify the squeeze scale inhibitors will be introduced including brine compatibility, static jar test, dynamic loop test and coreflood test to qualify the scale inhibitor for squeeze application. This polymer scale inhibitor showed good efficiency in both sulphate and carbonates scale inhibition under the test conditions, along with very good adsorption and desorption property without formation damage. This paper will give a comprehensive study of oilfield scale squeeze treatment for challenged well, which includes molecular synthesis, program of lab qualification, field design, deployment, application and monitoring. In addition, the mechanisms of squeeze life enhancement through molecular design, squeeze life enhancement and squeeze design will be addressed. TX 75083-3836, U.S.A., fax +1-972-952-9435