The Use of Sea Water in Well Cementing

Abstract

The performance of cement slurries using sea water can be predictable to a safe degree. Using sea water reduces placement time, increases early strength development, and shortens waiting-on-cement time. The effects of sea water on accelerators, retarders, fluid loss, and dispersant additives are discussed. Introduction This study shows that if sea water is used in place of fresh water for mix water in cementing systems, the setting rate of cement is accelerated. This affects cement thickening time, early strength development, and waiting-on-cement time. Using sea water also affects the prehydration of bentonite and the activity of accelerators, retarders, fluid loss, and dispersant additives. Also, improved bonding characteristics are indicated. Uncontaminated waters from seven oceans under current drilling activity are analyzed and are shown to be very similar in composition. For preliminary laboratory testing with cements, the composition of sea water can be approximated by the ASTM standard sea water. Also, a complete analysis of a specific sea water can be obtained by measuring only the chloride content. The other major constituents can be calculated from this chloride ion. Other investigators have found that, for most practical purposes, the ratios of all major components of sea water to chlorides are constant. Cement slurries for well completions generally perform best when mixed with fresh water. It is generally believed that if the water is potable, it is satisfactory for cements. This practice is followed generally on land operations, where practical and economical, and has been the practice in practical and economical, and has been the practice in several offshore areas. However, with increased offshore drilling activities, the use of sea water for mixing cement slurries for down-hole cementing applications has increased significantly. Sea water is being used as the mix water for casing, liner, and squeeze cementing operations. Also, because of the large loads placed on offshore platforms, it is now the practice in many cases to grout the piles to the jacket structures for effective load transfer. Some of these grouts are mixed with sea water. The reasons for this increased application of sea water become readily apparent when the advantages of sea-water cementing are examined. The advantages includeready availability,lower costs because transportation is eliminated, andreduced fresh-water storage on offshore platforms. Perhaps the most significant effect on cement performance is caused by the presence of sodium chloride in performance is caused by the presence of sodium chloride in sea water. The effect of sodium chloride on physical properties of oilwell cements has been discussed by Ludwig properties of oilwell cements has been discussed by Ludwig and by Slagle and Smith. These are both excellent presentations on the effect of sodium chloride, but generally presentations on the effect of sodium chloride, but generally only limited data on sea water were included, or the concentration of the salt studied was considerably higher than salt concentration in sea waters. Therefore, a better definition of the effects of sodium chloride and other salts in sea water on the various physical properties of cement in the slurry state and the set state was required. Sea-Water Composition The concentration of dissolved materials in ocean water varies with location and with seasons of the year. Sea water is diluted by rivers, rain, or melting ice, or is concentrated by evaporation. Sea water also contains all types of suspended material, such as colloidal and larger particulate minerals, insoluble organic compounds, and particulate minerals, insoluble organic compounds, and living creatures. JPT P. 759