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This paper is focused on a dual approach for silica scale control, inhibition and dissolution by use of designed chemical approaches. Inhibitors that are tested include the polyaminoamide STARBURST dendrimers (PAMAM) of generations 0.5, 1.0, 1.5, 2.0, and 2.5. Of these, only the NH 2 -terminated ones (PAMAM-1.0 and 2.0) show significant inhibitory activity, in contrast to COOH-terminated ones (PAMAM-0.5, 1.5, and 2.5), which show virtually no inhibition performance. The synergism between the above dendrimers and an anionic polyelectrolyte (poly(acrylamide-co-acrylate) copolymer) is also described. Addition of poly(acrylamide-co-acrylate) copolymer in silica supersaturated solutions containing PAMAM-1 or 2 alleviates the appearance of silica-PAMAM insoluble precipitates, resulting in stable colloids. The paper also describes silica dissolution approaches, as an alternative to inhibition, by using nonhazardous additives based on polycarboxylates with one to five -COOH groups (acetate, oxalate, citrate, diethylenetriaminepentaacetate, and others), mixed polycarboxylates/phosphonates (2-phosphonobutane-1,2,4-tricarboxylate), and amino acids (L-histidine and L-phenylalanine). Their reactivity is linked to their chemical structure in this structure/function study. The presence of additional chemical groups (e.g., -PO 3 H 2 , -NH 2 , or -OH) in the dissolver molecule augments the dissolution process.

The formation of barium sulfate (BaSO4) in the oilfield is known to occur as a precipitation process from the aqueous phase within oil production facilities. This barite deposition causes many problems related to flow assurance. In this paper, the initial stages of barium sulfate deposition on a metallic surface are investigated. The mass rate of deposition of barite on the surface was measured using a quartz crystal microbalance (QCM). The morphology of the deposited BaSO4 was then observed directly with an atomic force microscope (AFM) and the main crystal faces of barite were identified. Both the formation kinetics and the crystallography of the deposited barium sulfate were studied at three supersaturation ratios and in the presence and absence of 2 chemical scale inhibitors, namely, polyphosphino carboxylic acid (PPCA) and diethylene triamine penta acetic acid (DETPMP). In addition, the precipitation of the barite in the bulk phase was also monitored (by turbidity measurements) thus giving a more complete description of the overall bulk/surface barium sulfate kinetics. PPCA proved to be an effective barite inhibitor both at the surface and in the bulk phase in these measurements. DETPMP did not perform so well but there are several reasons why this may be so in such early time experiments and these are discussed in the paper. Thus, such experiments must be interpreted with some caution when we are relating the results to the oilfield scale system. In the industrial application addressed here, the brine system is very specific in that it is at relatively high ionic strength, the divalent cations (Ca2+/Mg2+/Sr2+) play an important role and the supersatuaration ratios of barite are very high. However, barite deposition is currently a very significant problem in the oil and gas industry, and this paper presents findings that will contribute to better ways of managing barite scale in the future.

No abstract

The effect of various environmentally friendly chemical additives on the dissolution of colloidal silica is systematically studied. These silica scale dissolvers are principally polycarboxylates with one to five -COOH groups, mixed polycarboxylates/phosphonates and aminoacids. Based on these results, an effort is made to link their dissolution performance to structural features in this structure/function study. Presence of additional groups (eg. -PO 3 H 2 , -NH 2 , or -OH) in the dissolver molecule augments the dissolution process.