Calcium sulfate scale is one of the challenges that face production stability in the oilfield industry as it is one of the most challenging scales to manage. Sulfate-scales are very hard to dissolve because of their low solubility-product. This work studies the dissolution capacity of different chemical additives and recipes on calcium sulfate scales. In this work, the maximum dissolution capacity (gram of scale/mole of chelating agent) of various chemical additives and recipes will be studied to evaluate the efficiency in the dissolution of Calcium Sulfate scales. Several experiments were conducted at multiple doses, pH, and in-presence of a catalyst. Potassium Carbonate was used as a catalyst in the dissolution of Calcium Sulfate scales. The performance of each additive was studied in a catalyzed and non-catalyzed pathway and with various. A Series of experiments conducted showed that parameters such as the additive-dose, pH, and a catalyst affect the dissolution efficiency. The dissolution performance efficiency of each additive (Lactic Acid, Citric Acid, L-Glutamic Acid-N, N-diacetic Acid (GLDA), and Gluconic Acid) was compared to the additive performance efficiency under a catalyzed pathway in a formulated recipe. The outcome of this work will contribute to the economic value added by finding the most efficient and cheap recipe to remove Calcium Sulfate scales from the wellbore.
Scale is considered as one of the major concerns in the oilfield industry. Usually, scale formation causes several issues such as: reduced production, formation damage, jeopardizing well integrity, and causing damage to assets such as artificial lift equipment. Therefore, a scale inhibition operation has to be conducted to sustain oil and gas production by assuring the flowing conditions of the reservoir and production assets. Scale inhibition in oilfield industry is carried out in one of four ways: 1- squeezing the inhibitor inside the formation, 2- continuously injecting the inhibitor through a capillary tubing, 3- apply an encapsulated inhibitor in the rat hole, 4- applying batch treatments. In this study, we are evaluating various treatment designs for the scale inhibition through the squeezing technique in terms of efficiency and lifetime. The efficiency of scale inhibition squeeze treatments is bound to a certain lifetime which depends on the interaction between the inhibitor and the reservoir rock. The inhibitor interacts with the rock in an adsorption fashion, then it desorbs to maintain a certain concentration in the aqueous portion of the produced fluids; thus, inhibiting scale deposition. When squeezing the scale inhibitor deep inside the reservoir, the inhibitor has a greater surface area to adsorb onto; therefore, less of it will be retained when flowing the well after the operation. The drawback of the squeeze technique is the duration, and the inhibitor loss right after the operation, the greater the inhibitor production the shorter the treatment lifetime. Squeezing the treatment deep inside the formation has reduced the inhibitor concentration; thus, increased the treatment estimated lifetime by almost 5 folds.
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