"Silicalock" - A Novel Sand-Control Process for Gas Wells

Abstract

Summary A novel sand-consolidation technique especially suited for the prevention of sand influx in gas wells is described. This technique-"Silicalock"-has the advantage of being a single-chemical one-phase dynamic treatment that can be carried out through tubing and that leads to reduced chances of productivity impairment. The results of three successful field tests also are described. Introduction The importance of natural gas as an essential and clean source of energy has increased considerably in recent years. Much of this gas is produced from loosely consolidated sandstone reservoir that require some form of sand control. Experience in both field and laboratory has shown that the probability of sand influx increases as a reservoir is depleted and pore pressure decreases. Production facilities may be, designed to cope safely with the production of small amounts of sand. However, sand production over a long time is generally not acceptable since it often leads to serious erosion problems. Furthermore, some of the produced sand will normally remain in the wellbore, which may result in a sand fill that adversely affects the well's productivity. The standard forms of sand control, primarily developed for oil wells, also may be applied to gas wells. These include(1) beaning back production, (2) mechanical methods such as wire-wrapped screens with and without gravel packs, and (3) consolidation processes in which the sand grains are "glued" together. However, none of these methods makes allowance for the special conditions found in gas wells, and they are therefore not optimal. The Shell group of companies has been exploiting several large gas fields during the past decade, including the giant Groningen field [operated by the Nederlandse Aardolie Mij. (NAM)] where about 280 wells can produce up to 480 × 10 std m /d during peak winter production periods. A view to possible future sand problems justified the star, of development of a sand control process especially geared to the conditions prevailing in gas wells. This has resulted in the novel chemical technique "silicalock" described in this paper. The process is based on the following reaction. SiCl4 + - 2H20- silica cement +4 HCl. The water is supplied by the connate water naturally adhering to the sand grains. The process differs from previous sand consolidation processes involving silicon tetrachloride in that it operates from the gas phase. The "silicalock" technique consists in vaporizing liquid silicon tetrachloride into a stream of high-pressure nitrogen gas. The mixture is injected into the well, preferably through coiled tubing. Immobile water present in the near-wellbore region is converted into silica cement, which cements the grains together, thus preventing any (further) influx of sand into the well. JPT P. 2087^