Advances in LDHIs and Applications

Abstract

This paper is to represent reviews of low dosage hydrate inhibitor's (LDHI) evolution and advances, and to provide a general guide for LDHI considerations, historically, hydrate risk has been managed by keeping the fluids warm, removing water, and/or by injecting thermodynamic hydrate inhibitors (THI), commonly methanol or glycol. THIs require high dosage rate therefore production systems can reach a treatment limited by supply, storage, and umbilical injection constraints. Besides, high dosage of MeOH can cause crude contamination for downstream refineries, which may result in penalty. Over last two decades LDHIs have been extensively researched and developed as an alternative hydrate management chemical for oil and gas industry. LDHIs are divided into two main categories; Kinetic Hydrate Inhibitor (KHI) and Anti-Agglomerant (AA), both have been successfully used in field applications, but each comes with their unique challenges for applications, OPEX and CAPEX considerations. LDHIs have proven track records in numerous fields in their performance, either as stand-alone chemical treatment or reducing amounts of methanol/glycol usage, which has directly resulted in CAPEX and OPEX reduction. LDHIs have been instrumental in managing risks of early water breakthrough, high cost of THI storage and transportation, HSSE concerns around THI handling, and undersized pump capacity for required chemical volumes. Switching to LDHIs also offers an economic advantage by reducing umbilical line diameter. Latest advances in the LDHI technology is breaking barriers and pushing limits. The paper summarizes historical advancements in LDHIs over the last two decades, discusses application advantages and limitations, and the criterions to consider for selecting LDHIs.

N-Vinyl Caprolactam/Maleic-Based Copolymers as Kinetic Hydrate Inhibitors: The Effect of Internal Hydrogen Bonding

“…We have begun a program to develop multi-functional chemicals in an attempt to treat gas hydrates, corrosion, and scale, which are all water-based problems. Regarding the first issue, we have been designing and testing kinetic hydrate inhibitors (KHIs) as a method to prevent gas hydrate solids from forming in flow lines. − KHIs delay the hydrate formation process at the nucleation and crystal growth stages. , KHIs have been shown to both increase the nucleation work required to form critical nuclei and increase the effective number of sites where nucleation could occur …”

Review of Kinetic Hydrate Inhibitors Based on Cyclic Amides and Effect of Various Synergists

“…An uninterrupted gas flow is essential to maintain efficiency in natural gas pipelines and other processing plants. − Usually, both the hydrocarbon gas and water are present in the fluids produced and transported. − Hydrate plugs can easily form at low temperatures (<293 K) and high pressures (>4 MPa) with diverse water/gas ratios. − Hydrate plugs can obstruct the pipelines, which can eventually lead to pipeline failure. , A conducive hydrate-forming environment is present in permafrost and the continental shelf regions. Offshore flowlines often operate in these regions and thus are prone to plugging due to hydrate formation. ,,,, The removal of hydrate plugs, if formed, from pipelines is inefficient and time-consuming. ,, Substantial damage to machinery can happen, especially when hydrate plugs are propelled due to significant pressure difference, creating a major safety and environmental hazard . Hence, to safeguard the cost-efficient working of pipelines, hydrate plug accumulation must be effectively prevented. − The most effective solution for hydrate plug inhibition is the use of hydrate inhibitors. − …”

“…In a BP-operated Eastern Trough Area Project (ETAP), the application of a KHI instead of a THI provided a savings of 40 million U.S. dollars . Shell also reported a successful KHI implementation in their Popeye subsea well . The well needed 250 BPD of the THI to inhibit the hydrate.…”

Hydrate Risk Management in Gas Transmission Lines

“…Through collaborative efforts between industry and academia, kinetic hydrate inhibitors (KHIs) became the second chemical means by which to protect transmission lines from hydrate formation, where a few weight percent of early generation KHI in the aqueous phase could protect against hydrate formation for at least 50 h at up to 10 K below the hydrate phase boundary . Over the past 25 years, most efforts around KHI development have focused on improving the effectiveness of known chemistries (quantified in the laboratory by longer periods of suppression at greater subcooling from the phase boundary); their environmental profile, including the ecotoxicity, biodegradability, and/or bioaccumulation of the active chemical and any solvation package used for injection; and the method and interpretation of scaled-down laboratory tests − to inform the minimum dosage required for the field …”

“…To estimate the minimum effective dosage of the nominated commercial AA, high-pressure rocking cells , are typically used in the industry, as they have an established track record of conservative results and maintain the ability to inform basic environmental risks when chemical injection is being considered. , Being produced through both custom manufacturing and retail vendors, high-pressure rocking cells are typically configured as isochoric cylindrical cells containing a stainless-steel ball that oscillates between end plates as the cell is “rocked” at a constant rate; hydrate formation is typically controlled by submerging the rocking cell in a temperature-controlled laboratory bath.…”