Proposal

Recent technical and logistical challenges in the Gulf of Thailand have driven the development of a new approach to lightweight cementing. The industry has evolved from numerous and complicated dry cement blends being used on 45-day well constructions to the present minimum liquid additive, lightweight, single slurry approach used on 5-day wells. As nearly all wells are now slimhole monobores, the cement job has become one of the most important operations in the life of the well. The absence of packers or other isolation devices means that the cement job functions as a primary pressure barrier and is the only technique to isolate the numerous sands in each well. This combined with the logistic issues of fast offshore batch drilling exact a premium on cementing products and the entire cementing process itself.

For offshore applications it is advantageous to use an all-liquid system so as to avoid relying on mud pits to blend mixwater, to avoid the confusion of multiple dry blends in the field and to have flexibility to make last minute changes in slurry design. Recently a new approach to lightweight cementing using Multifunctional Liquid Additives (MLA’s) was developed so that on-the-fly mixing is possible with only three to four streaming additives. MLA’s have reduced what used to be a complicated set of dry blends to a few liquid additives. By simply adjusting the cement:water ratio and MLA concentration, the same base slurries can be tailored for nearly any scenario. This approach has been used recently in PTTEP’s Arthit gas field to construct a 1.60 SG. production string slurry at 190°C. The same additives work for shallow gas where temperatures are over 150°C cooler. Because the systems are so robust, slurry charts have been implemented such that the rig can decide what slurry to pump based on a given bottom hole circulating temperature (BHCT) and desired thickening time.

This paper illustrates the various ways lightweight slurries using MLA technology have created a new approach to offshore well construction in The Gulf of Thailand.

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