Oil well cementing uses a variety of organic additives such as dispersing agents, retarders or fluid loss control additives. The later, which prevent interstitial water from filtering into the formation during cement placement, are generally polymer based. A widely used class of fluid loss control additive are the high molecular weight Sulfonated copolymers, generally comprising AMPS (2-Acrylamido-2-methylpropane sulfonic acid) copolymerized with Acrylamide (Am) or N, N′ Dimethylacrylamide (DMA). The mechanism of action of these polymers has been studied recently and it was demonstrated that adsorption onto the cement surface is crucial to achieve the required product performance. It was also shown that other solutes and admixtures present in the cement interstitial solution can hinder adsorption resulting in performance losses. Thus it has been recommended to incorporate an additional monomer containing strongly adsorbing units in the copolymer to enhance the interaction with the cement surfaces hence limiting competitive adsorption issues.

In this study we investigated the use of diblock copolymers comprising a short but strongly adsorbing block and a long second block of DMA-AMPS as a potential new class of filtration control agent. We showed that diblock copolymers with much lower molecular weights than statistical polymers can provide satisfactory fluid loss control performance. Furthermore, it was demonstrated that these structured polymers show good formulation flexibility and deliver more robust performance in the presence of a wide range of admixtures and solutes.

Finally we focused on the analysis of the adsorption on cement of various formulation admixtures and how it affected the adsorption of our diblock copolymers. With the aid of an analytical method utilising size exclusion chromatography of collected filtrate from HPHT filtration cells, it was possible to have a direct access to a fluid loss polymer concentration in the filtrate even in the case of complex formulations.

Based on these studies, the mechanism of action of the diblock copolymers as fluid loss control agents is discussed with reference to that evoked for statistical polymers.

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