Removal of Iron Sulfide Scale with a New Formulation: A Field Application in a Sandstone Reservoir in Egypt

Abstract

Iron sulfide scale is a significant problem in the oil and gas industry whereas the iron sulfide deposition has an adverse impact to the production operations. The scale is present in various species with different iron to sulfur ratios. Iron sulfide species with high iron content is soluble in acids, whereas those rich in sulfur are almost insoluble in acids. East ZEIT oil wells have been produced for 20 years in Egypt. Scales with iron sulfides as the major components form in nearly every producing well. These scales have minor compositional but form at differing rates and thicknesses in the lower half of tubing string. Well East ZEIT-13 was completed initially in Nubia formation which is communicated with another formation called ‘’Lower Senonian’, whereas the drive mechanism is active water-drive. The formation is sandstone with the following specs: Lose, pale yellow, quartz, very fine to fine-grained, sub-rounded to rounded, and moderately sorted sand grains. The reservoir temperature is 300°F. The well was producing using a jet pump (JP), the production stopped due to scale formation. A workover started to replace the completion. The JP was used again to produce the well with very low productivity; +/-0.06 bbl/psi. The power fluid of the JP is oil with 1% water cut. The scale was expected to cover all the casing area below the tubing end until PBTD. A scale sample was obtained and analysis of the scale through XRD showed that the scale composition is as follows; 36% Marcasite (FeS2), 21% Greigite (Fe3S4), 17% Pyrite (FeS2) and 26% Siderite (FeCO3). Both pyrite and marcasite have a very low solubility in HCl, and the only available method of removal in the oil industry is milling. The milling operation failed to solve the problem, therefore, the production was stopped until finding an alternative solution. An effective treatment strategy proposed to remove the scale efficiently; the technical proposal was designed taking into consideration the complicated nature of the scale. Furthermore, the proposed treatments were conducted and placed using coiled tubing (CT). The first application using the SCSR-02 solution has been successfully carried out and the job results were outstanding. Production has been returned with an increment of 50% above its original rate. The well is producing natural flow without using the JP, and efficient cost/Bbl.

New Environmentally Friendly Acid System for Iron Sulfide Scale Removal

“…The DTPA formulation dissolved 85% of the scale at 70 • C for 48 h. They suggested several catalysts that can enhance the dissolution rate of the pyrite scale such as potassium carbonate, cesium formate, and cesium carbonate. Abou Baker et al [26] used a novel product that combines the effectiveness of chelating agent and dissolver of iron sulphide in actual field application (sandstone reservoir with a temperature of 149 • C). They concluded that the well production was returned with an increment of 50% above its original rate and the well was producing natural flow without using the jet pump.…”