Sequestering Agents for Prevention of Scale Deposition in Oil Wells
- R.C. Earlougher (Earlougher Engineering) | W.W. Love (Dowell Inc.)
- Document ID
- Society of Petroleum Engineers
- Journal of Petroleum Technology
- Publication Date
- April 1957
- Document Type
- Journal Paper
- 17 - 20
- 1957. Original copyright American Institute of Mining, Metallurgical, and Petroleum Engineers, Inc. Copyright has expired.
- 3.2.4 Acidising, 5.4.1 Waterflooding, 2.2.2 Perforating, 2.4.3 Sand/Solids Control, 6.5.2 Water use, produced water discharge and disposal, 4.1.2 Separation and Treating, 4.3.4 Scale
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Precipitation of insoluble mineral deposits, in and near the wellbore and on down-hole well equipment, lowers production rates considerably in many oil fields. Scale deposits have been prevented in industrial equipment by conditioning the water with phosphate sequestering agents. Such agents inhibit crystal growth so that, when the ions combine to form insoluble compounds such as calcium carbonate, calcium sulfate, and barium sulfate, these minerals remain in colloidal suspension.
A 12-to-40 mesh, granular phosphate has been used successfully to prevent such deposition in oil wells. The phosphate granules are mixed with the sand injected into the producing formation during fracturing treatments. Tests show that the phosphate is slowly dissolved by produced well fluids, preventing scale deposition within the formation and on down-hole well equipment. More than 30 wells have been treated by this special phosphate fracturing method, and production data indicate that the problem of formation plugging by mineral deposition is being effectively overcome.
A frequent oilfield problem is the well which declines sharply after being completed and tested for a good initial production rate. Often there is no apparent reason for the rapid decline, and the reservoir is known to hold large amounts of oil. In many of these cases, deposition of calcium carbonate, calcium sulfate, or barium sulfate may be curtailing production.
Mineral deposition occurs in the wellbore, in formation flow channels adjacent to the wellbore, and on down-hole well equipment such as pumps, rods, and screens. Such deposition may be caused by changes in reservoir equilibrium near the wellbore, or by the mixing of incompatible brines from different formations in openhole completions. These difficulties occur both in primary and secondary production wells.
Such deposits can sometimes be dissolved or disintegrated by acidizing, depending upon the amounts of carbonate they contain. If, however, the deposit consists principally of sulfates, it is usually necessary to fracture the well to overcome this obstruction.
A summary was made recently of the results of fracturing treatments on 187 waterflood production wells. This summary covers three years, and includes some treatments completed as recently as a few months ago. In virtually every case the remedial fracturing treatments were necessitated by mineral deposition in the well that plugged off the flow channels and reduced production.
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