Many Khuff reservoir gas wells in Saudi Aramco fields are classified as sour producers with H2S levels as much as 8 mol% and CO2 contents as much as 5 mol%. Despite being completed with carbon steel tubular, corrosion failure has not been a major issue even after more than 20 years of service. On the other hand, most wells are experiencing scale buildup in production strings, causing an estimated production loss of up to 7 MMscfd for some wells. Besides, scale deposits are limiting well access for downhole surveillance and intervention. Significant efforts have been taken to understand the scale formation mechanisms. Extensive scale samples have been collected and characterized over the years. Although the exact chemical compositions change from well to well and also vary with depth in a given well, the scale deposits are usually mixtures of many compounds and often dominated with iron sulfide minerals. These iron sulfides include pyrrhotite, troilite, mackinawite, greigite, pyrite and marcasite. Other iron containing compounds, such as iron oxide and iron carbonate, are also found in significant amounts in most cases. Additionally, mineral scales, such as calcium carbonate and barium, strontium and calcium sulfate, are often present. Both mechanical and chemical methods have been applied for scale removal. Chemical dissolvers based on concentrated hydrochloric acid have been the most effective solvents. This types of dissolvers are very corrosive to well completion metallurgy at elevated temperatures, and the spent acids can cause severe formation damage due to re-precipitation of iron sulfides, if entering the near wellbore area. The rapid generation of large amounts of H2S gas creates a potentially lethal health hazard. This paper presents an effort to identify alternative dissolvers with high dissolving power and low corrosivity to carbon steel.
Blockage of gas flow lines by gas hydrates is a major problem in the oil and gas industry, which leads to severe safety issues and causes economic losses. Kinetic hydrate inhibitors (KHIs) are water-soluble polymers that are employed to circumvent this problem due to their effectiveness at low dosage, which makes logistics (transport, storage, and pumping) less costly particularly in offshore operations. However, some of the currently available KHI polymers have subcooling constraints against class I hydrates in high sour gas conditions, which limit their utilization. In this Article, we report a new KHI copolymer synthesized from N-acryloyl pyrrolidine and N-acryloyl piperidine monomers. Detailed characterization and compatibility studies were carried out using a variety of techniques and tests. The rocking cell test demonstrated the new formulation’s effectiveness to a high subcooling temperature of 8.5 °C at 140 bar of a gas mixture containing a high concentration of CO2 and H2S. The performance of the copolymer was investigated at 2% and 3% dosage, where the increased dosage of copolymer showed a higher subcooling temperature. Collectively, these results set a stage for the design, development, and evaluation of a new type of polymers as an effective KHI.
Corrosion poses safety and operational challenges in the oil and gas field, particularly in a sour environment. Corrosion inhibitors (CIs) are thus employed to protect the integrity of industrial assets. However, CIs have the potential to dramatically impair the effectiveness of other co-additives, such as kinetic hydrate inhibitors (KHIs). Here, we propose an acryloyl-based copolymer, previously used as a KHI, as an effective CI. The copolymer formulation provided a corrosion inhibition efficiency of up to 90% in a gas production environment, implying that it can reduce or even eliminate the need for an additional dedicated CI in the system. It also demonstrated a corrosion inhibition efficiency of up to 60% under field-simulated conditions for a wet sour crude processing environment. Molecular modeling suggests that the enhanced corrosion protection is imparted by the favorable interaction of the heteroatoms of the copolymer with the steel surface, potentially displacing adhered water molecules. All in all, we show that an acryloyl-based copolymer with dual functionalities can potentially overcome issues caused by incompatibilities in a sour environment, resulting in significant cost savings and operational ease.
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