ABSTRACT:

As the activity for new underground gas storage wells is increasing, the operations scenario also is rapidly changing, introducing different requirements than conventional production activity. In Italy, the main goal of new well construction campaigns is not only to increase overall gas storage capacity, but also to better handle the reservoirs and optimize their use. Infilling wells in depleted unconsolidated sandstone is the main challenge to face for current underground gas storage activity in Italy, as they may have to be drilled through shale or shaley sand unknown sections. Sand control is absolutely required to guarantee well longevity and constant production rates. The high peaks of production require large-bore horizontal open-hole wells. The major challenge in completing such reservoir types is how to treat the shale lobes encountered while drilling the main reservoir. Clays can cause troubles during conventional open-hole gravel packs, leading to bore instability or screen plugging. They can also jeopardize the well longevity as zonal isolation, required to limit fines production, is not easy to obtain with conventional gravel-pack equipment. In this paper we present a different approach to underground gas storage wells. A case history for expandable screens operations will be presented to evaluate the benefits and limits of this technology in treating unconsolidated sandstone for underground gas storage wells. Three main advantages will be shown. The first benefit is the mechanical zonal isolation achieved through the use of expandable tubular and packers. The technology not only allows isolating the shale below the casing shoe but also straddling shale or water saturated sand sections between two main reservoir sections to reduce possible fines production during well life. This solution, compared to a chemical approach toward stabilizing the shale, has the main advantage of guaranteeing a mechanical straddle-type and, therefore, longer, well longevity. A second benefit would be reduction of operational risks. Not having to displace to brine or circulate clearly alleviates borehole instability issues. A third advantage of expandable technology is to allow larger bores to better handle the required high peaks of production and injection. The paper will show through actual case history how the above-mentioned targets have been achieved and how the operating procedures for the new technology have been finetuned. Challenges for future wells will be also discussed

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