SPAs are polymers that are available in various ranges of molecular weight and offer high temperature stability. SPAs of low molecular weight are deflocculants for clays and are used to improve fluid loss
control by that mechanism. SPAs of very high molecular weight are effective for fluid loss control by increasing the viscosity of the filtrate and by plugging in the cake. They are sensitive to calcium ions, especially at high molecular weight. Derivatives of SPA which are less sensitive to ionic content are available as proprietary thinners and fluid loss additives. An example is the AMPS type polymers.
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