Cementing in Front of Soluble Salt Zones

Abstract

Abstract Cementing in front Salt Zones requires an appropriate cement slurry design to assure minimum dissolution of the formation by the cement slurry and also minimum deleterious impact on the properties of the cement. The influence of halite on the cement slurry properties is already well discussed in the literature, but there’s no much information regarding the influence of other salts like taquidrite, carnalite, which are much more soluble than halite and are found in Brazil Offshore Fields. The first stage of the work consisted in evaluating the influence of different levels and types of salt on the hydration process and its effects on the behavior of the main physical properties. It was produced fourteen cement pastes, five of them containing NaCl at the contents of 5, 10, 15, 20 and 36% by weight of water and eight containing KCl at contents of 1, 3, 5, 7, 10, 15, 20 and 34% by weight of water. It was also prepared a cement slurry with no salt added to be used as reference. The dissolution rate of the different salts core formation in these cement slurries was determined. The influence on the cement slurry properties, such as free fluid, thickening time, compressive strength and rheological parameters due to halite, carnalite and taquidrite incorporation were also determined. This paper presents the studies conducted to design cement slurries for cementing well through salt layers (halite, carnalite and taquihydryte) located in the Aguilhadas Field in Northeast, Brazil. Based on the results, about 500 m of salt were cemented with a semi-saturated cement slurry which provided an excellent quality of the cementing, proved by acoustic logs. Salt cores of halite, carnalite and taquihydryte were used to determine the dissolution rate of salt into the cement slurry. X-Ray tomography was used to visualize and to quantify the salt dissolution in the dynamic tests. The shear bond strength between halite core and hardened cement slurry with 15% NaCl was determined showing good results.