New Environmentally Friendly Acid System for Iron Sulfide Scale Removal

Abstract

Iron sulfide scale is a common problem in the oil and gas industry. The precipitation of the iron sulfide scale on the well completion tools or inside surface flow lines restricts the flow of the produced fluids and might affect the integrity of the pipelines or the surface and subsurface tools. Failure of the downhole completions tools will not only reduce the production rates but it might require workover and remedial operations that will add extra cost. The main objective of this paper is to evaluate a new environmentally friendly acid system (NEFAS) for iron sulfide scale removal using an actual field sample. The scale sample collected from a natural gas well is dominated by pyrrhotite (55%) in addition to calcite (21%), pyrite (8%), and torilite (6%) with minor traces of hibbingite, siderite, geothite, akaganeite, and mackinawite. High-temperature solubility tests were performed by soaking 2 g of the scale field sample with 20 cm3 of the NEFAS under static condition at 125 °C for different time periods (2, 6, 12, 18, and 24 h). The solubility results were compared with commercial solutions for iron sulfide scale removal such as hydrochloric acid (15 wt.%), glutamic acid diacetic acid (GLDA, 20 wt.%), and high density converters (HDC-3) under the same conditions. The corrosion test was performed at 125 °C for the developed solution after mixing with 2 wt.% corrosion inhibitor (CI) and 2 wt.% corrosion intensifier (CIN). The results were compared with HCl (15 wt.%) under the same conditions. NEFAS consists of 75 wt.% biodegradable acid at pH of 0.04. NEFAS achieved 83 g/L solubility of iron sulfide scale after 6 h at 125 °C under static conditions. The solubility efficiency was very close to 15 wt.% HCl after 24 h where the solubility was 82 and 83 g/L for NEFAS and HCl, respectability. HDC-3 and GLDA (20 wt.%) achieved a lower scale solubility; 18 g/L and 65 g/L respectively, after 24 h. NEFAS achieved a corrosion rate of 0.211 kg/m2 after adding the CI and and CIN compared to 0.808 kg/m2 for HCl. The new environmentally friendly biodegradable acid system provides efficient performance for the scale removal without harming the environment and causing any side effects to the operation.

Barium Sulfate Scale Removal at Low-Temperature

“…In addition to that, the performance of HCl was found efficient in specific scale types as zinc sulfides [39], pyrrhotite, and troilite of iron sulfides. However, the results did not show great solubility with sulfate scales as strontium, calcium, and barium [20,21]. Organic acids as citric acid, maleic acid, formic acid, and acetic acid were employed for the scale removal at highpressure high-temperature reservoirs [40][41][42].…”

“…The descaling process should be designed from technical and economic aspects [18,19]. The scale precipitations might lead to production reduction or shutdown [20], and hence, utilizing the scale inhibitors might be efficient for preventing the scale deposition [7,21,22]. The proper chemical design for the scale inhibitors has shown successful results for field applications [23].…”

Development of a Unique Organic Acid Solution for Removing Composite Field Scales

“…On the other hand, economics should consider the chemical and/or mechanical job cost and solution volume to scale mass ratio. 18 , 19 …”

“…The scale mass to removal solution liquid ratio is considered a critical parameter for the technical and economic design for the field descale job. 19 , 49 The scale precipitations mass was calculated from the diameter dimension reduction because of the scale and its density. 14 , 50 The main objective of the descaling operation is to achieve a higher dissolution rate with less dissolver amount for cost-saving.…”

“…Commonly, the corrosion test is performed for 6 h as this time is sufficient for the descale jobs in the field. 19 The coupon and solution should be extremely observed by the end of the test to get the indications about the precipitations and color change in the solution and that will help for further analysis.…”