Oilfield Scales

Calcium carbonate is a slightly soluble salt occurring in nature in the form of minerals such as calcite, limestone, dolomite, and marble. The solubility is much greater in adds. Carbon dioxide in the air or within oil formations dissolves in water to form carbonic acid, HjCOj. This acid converts the carbonates in calcium carbonate to soluble bicarbonates that can be dissolved in water. 

The amount of COj that will dissolve in water is proportional to the amount of COj in the gas over the water and the pressure of the system. So, if either the system pressure or the percentage of COj in the gas were to increase, the amount of CO2 dissolved in the water would also increase, allowing more calcium carbonate to be dissolved. 

The reverse is also true, and is one of the major causes of CaCOj scale deposition. At any point in the system where a pressure drop is taken, COj comes out of solution, and the pH of the water rises. This shifts reaction (6.3) to the left and may cause CaCOj precipitation. If the pH is lowered by the use of any acid, the solubility of calcium carbonate is increased the acid does not have to be carbonic acid from the solution of carbon dioxide in water. Any increase in alkalinity, on the other hand, increases the tendency to form a precipitate. 

Contrary to the behavior of most materials, calcium carbonate becomes less soluble as the temperature increases the hotter the water gets, the more likely CaCOj scale will form. 

Water that cools as it flows up to the tubing will not deposit carbonate because of temperature change, although loss of COj from the water can be of concern. The same water in contact with a heater tube may deposit scale readily on the fire tube. The increase of temperature in water injection wells can result in carbonate scale deposition. 

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N. P. Chilcott, D. A. Phillips, M. G. Sanders, I. R. Collins, and A. Gyani. The development and application of an accurate assay technique for sulphonated polyacrylate co-polymer oilfield scale inhibitors. 2nd Annu SPE Oilfield Scale Int Symp (Aberdeen, Scotland, 1/26-1/27), 2000. 

I. R. Collins. Scale inhibition at high reservoir temperatures. In Proceedings Volume. IBC Tech Serv Ltd Advances in Solving Oilfield Scaling Int Conf (Aberdeen, Scotland, 11/20-11/21), 1995. 

Hartog F., Jonkers G., Schmidt A., and Schulling R. (2001) Lead deposites in Dutch natural gas systems. In Third International Symposium on Oilfield Scale, Aberdeen, Scotland. 

Sorbie, K. S., Mackay, E. J. 1997. Mixing of injected, connate and aquifer brines in wateiflooding and its relevance to oilfield scaling. In Journal of Petroleum Science Engineering, 27, pp. 85-106. 

However, the use of chain transfer agents containing at least one P-H bond, allows to produce polymers which combine excellent activity as oilfield scale inhibitors with good biodegradability, often in excess of that required by the OECD 306B standard (11). 

Polymers which contain phosphorus end capping groups can have a desirably high biodegradability as weU as being effective as oilfield scale inhibitors (9). 

The invention of Heath et al. relates to novel phosphonate allyl monomers, made from reaction of an unsaturated oxirane with amine- or hy-drojyl-functionalized phosphonic acids (Scheme 3.21). These monomers were copolymerized with other unsaturated species (acrylic acid, maleic acid, acrylamide, or monomer derivatives of sulfonic acid, etc), yielding phosphonate polymers or oligomers. Phosphorus-containing monomers were incorporated at a ratio of 0.1-30% and polymerized in aqueous media. The final polymers had a molecular weight of 800-30 000 g mol . With their phosphonic acids groups (free acid or salts forms), they are of particular use as oilfield scale inhibitors. 

Although field conditions vary widely, oilfield scale inhibitors for BaS04 inhibition must in general meet the following requirements ... 

There are several gas-well fields that produce hydrocarbon gas associated with very high TDS connate waters. Classical oilfield scale problems (e.g., calcium carbonate, barium sulfate, and calcium sulfate) are minimal in these fields. Halite (NaCl), however, can be precipitated to such an extent that production is lost in hours. As a result, a bottom-hole fluid sample is retrieved from all new wells. Unstable components are "fixed" immediately after sampling, and pH is determined under pressure. A full ionic and physical analysis is also carried out in the laboratory. 

R. T. Barthorpe. The impairment of scale inhibitor function by commonly used organic anions. In Proceedings Volume, pages 69-76. SPE Oilfield Chem Int Symp (New Orleans, LA, 3/2-3/5), 1993. 

L. S. Boak, G. M. Graham, and K. S. Sorbie. The influence of divalent cations on the performance of BaS04 scale inhibitor species. In Proceedings Volume, pages 643-648. SPE Oilfield Chem Int Symp (Houston, TX, 2/16-2/19), 1999. 

L. Yang and B. Song. Phosphino maleic anhydride polymer as scale inhibitor for oil/gas field produced waters. Oilfield Chem, 15(2) 137-140, June 1998. 

Y. B. Zeng and S. B. Fu. The inhibiting property of phosphoric acid esters of rice bran extract for barium sulfate scaling. Oilfield Chem, 15(4) 333-335,365, December 1998. 

Yuan, D. and A. C. Todd, 1991, Prediction of sulphate scaling tendency in oilfield operations. SPE Petroleum Engineering 6, 63-72. 

The Mesopotamian campaign against the Turks developed from a small-scale operation into one that absorbed considerable resources. An Indian Army division was dispatched to the head of the Persian Gulf in October 1914 to protect the oilfields at Abadan (of particular interest to the Admiralty following the decision to build oil-burning warships) and to prevent the expansion of Turkish influence towards India. The... 

Some oilfield waters can be plotted on a scale where the maximum lengths of the horizontal lines represent 100 meq of sodium and chloride ions and 10 meq of each of the other ions. For highly concentrated... 

Mixing of unlike brines can cause the precipitation of sulfates of barium, strontium, and calcium. This hard scale, which is a nuisance in oilfield flow lines, often can be explained by leaky casing. Soft scale, composed of calcium carbonate, usually is caused by the loss of dissolved carbon dioxide from the brine during pressure reduction. 

Despite the variety of geological differences in these oilfields, however, the Jurassic sandstones of the northern North Sea share common features, such as organic-rich Upper Jurassic source rocks and feldspar-rich reservoir sandstones, which may help explain some of their diagenetic similarities. These common threads also hint that large-scale diagenetic processes, which might be obscure or unrecognizable on the field scale, may become... 

The history of Shell as a real oil enterprise began in early 1890, when Marcus Samuel Junior made a visit to Batum on the Black Sea from where Russian oil from Baku was imported. The businessman was very impressed by the scale of operations. He saw a large market for kerosene in the Far East where it was used for lamps and cooking. Unfortunately, American Standard Oil Trust had a monopoly on the business. So, Marcus had to find a way to undercut prices. Quite separately, the Dutch company, Royal Dutch Petroleum Company, was formed to develop an oilfield in Pangkalan Brandan in Sumatra. Established in the Hague, it enjoyed the support of King William III of the Netherlands. 

Chemphonate. [Chemron] Phosphonic and phosphoric acids and salts scale inhibitors for oilfield prod. 

Chemphonate. [Chmmtm] Phosphonic and pho horic adds and salts scale inhibitors fix oilfield jxod. 

Crabtree, M., Eslinger, T., Fletcher, P., Johnson, A., King, G. 1999. Fighting Scale - Removal and Prevention. In Oilfield Review, Autumn 1999 pp. 30-45. 

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