Hydrate Prevention Strategies and the Associated Cost in the Gulf of Mexico

With the petroleum industry endeavoring to develop promising oil and gas in deeper water, gas hydrates prevention is a serious concern for oil and gas producing companies producing at conditions in the hydrate region. This paper details lessons learned from the successful field deployment of AA LDHI and proper implementation strategies used for 3 different practical fields as case studies in the Gulf of Mexico. From the 3 field experiences, the AA LDHI has been used to replace the conventional thermodynamic hydrate inhibitor due to its numerous benefits during steady state operations and transition operations where AA LDHI is injected prior to extended shut in and restart for fields producing at low water cut. However, the strategy to develop a cost effective chemical management of hydrates for fields producing at high water cut is by pumping methanol or diesel to push down the wellbore fluid below the mud line during planned and unplanned shut-ins to delay water production, it also secures the riser with non hydrate fluids. This illustrates how the AA LDHIs are used in conjunction with more conventional hydrate management approaches to reach an optimal cost effective field hydrate management solution. However, this shows that the key to overall success of hydrate prevention is a full integration of a good front end design, a comprehensive deployment and an effective down hole monitoring system.

Experimental and density functional theory computational evaluation of poly(N-vinyl caprolactam-co-butyl methacrylate) kinetic hydrate inhibitors

Natural gas hydrate inhibitor has been serving the oil and gas industry for many years. The development and search for new inhibitors remain the focus of research. In this study, the solution polymerization method was employed to prepare poly(N-vinyl caprolactam-co-butyl methacrylate)(P(VCap-BMA)), as a new kinetic hydrate inhibitor(KHI). The inhibition properties of P(VCap-BMA) were investigated by tetrahydrofuran(THF) hydrate testing and natural gas hydrate forming and compared with the commercial KHIs. The experiment showed that PVCap performed better than copolymer P(VCap-BMA). However,low doses of methanol or ethylene glycol are compounded with KHIs. The compounding inhibitors show a synergistic inhibitory effect. More interesting is the P(VCap-BMA)-methanol system has a better inhibitory effect than the PVCap-methanol system. 1% P(VCap-BMA) + 5% methanol presented the best inhibiting performance at subcooling 10.3 °C, the induction time of natural gas hydrate was 445 min.Finally, the interaction between water and several dimeric inhibitors compared by natural bond orbital(NBO) analyses and density functional theory(DFT) indicated that inhibitor molecules were able to form the hydrogen bond with the water molecules, which result in gas hydrate inhibition. These exciting properties make the P(VCap-BMA) compound hydrate inhibitor promising candidates for numerous applications in the petrochemical industry.

A new high performance gas hydrate inhibitor

In petroleum exploration and production operations,gas hydrates pose serious flow assurance,economic and safety concerns.Thermodynamic inhibitors are widely used to reduce the risks associated with gas hydrate formation.In the present study,systematic laboratory work was undertaken to determine synergistic effects between methanol and a Poly Vinyl Methyl Ether as Low Dosage Hydrate Inhibitors（LDHIs）.A valuable effect was discovered at a certain ratio of methanol to the low dosage hydrate inhibitor.

Kinetic hydrate inhibitor performance of new copolymer poly(N-vinyl-2-pyrrolidone-co-2-vinyl pyridine)s with TBAB

In oil and gas field, the application of kinetic hydrate inhibitors （KHIs） independently has remained problematic in high subcooling and high water-cut situation. One feasible method to resolve this problem is the combined use of KHIs and some synergists, which would enhance KHIs’ inhibitory effect on both hydrate nucleation and hydrate crystal growth. In this study, a novel kind of KHI copolymer poly（N-vinyl-2-pyrrolidone-co-2-vinyl pyridine）s （HGs） is used in conjunction with TBAB to show its high performance on hydrate inhibition. The performance of HGs with different monomer ratios in structure II tetrahydrofuran （THF） hydrate is investigated using kinetic hydrate inhibitor evaluation apparatus by step-cooling method and isothermal cooling method. With the combined gas hydrate inhibitor at the concentration of 1.0 wt%, the induction time of 19 wt% THF solution could be prolonged to 8.5 h at a high subcooling of 6℃. Finally, the mechanism of HGs inhibiting the formation of gas hydrate is proposed.

Insights into kinetic inhibition effects of MEG,PVP,and L-tyrosine aqueous solutions on natural gas hydrate formation

It is necessary to understand all the prerequisites, which result in gas hydrate formation for safe design and control of a variety of processes in petroleum industry. Thermodynamic hydrate inhibitors (THIs) are normally used to preclude gas hydrate formation by shifting hydrate stability region to lower temperatures and higher pressures. Sometimes, it is difficult to avoid hydrate formation and hydrates will form anyway. In this situation, kinetic hydrate inhibitors (KHIs) can be used to postpone formation of gas hydrates by retarding hydrate nucleation and growth rate. In this study, two kinetic parameters including natural gas hydrate formation induction time and the rate of gas consumption were experimentally investigated in the presence of monoethylene glycol (MEG), L-tyrosine, and polyvinylpyrrolidone (PVP) at various concentrations in aqueous solutions. Since hydrate formation is a stochastic phenomenon, the repeatability of each kinetic parameter was evaluated several times and the average values for the hydrate formation induction times and the rates of gas consumption are reported. The results indicate that from the view point of hydrate formation induction time, 2 wt% PVP and 20 wt% MEG aqueous solutions have the highest values and are the best choices. It is also interpreted from the results that from the view point of the rate of gas consumption, 20 wt% MEG aqueous solution yields the lowest value and is the best choice. Finally, it is concluded that the combination of PVP and MEG in an aqueous solution has a simultaneous synergistic impact on natural gas hydrate formation induction time and the rate of gas consumption. Furthermore, a semi-empirical model based on chemical kinetic theory is applied to evaluate the hydrate formation induction time data. A good agreement between the experimental and calculated hydrate formation induction time data is observed.

Experimental study of hydrogen sulfide hydrate formation: Induction time in the presence and absence of kinetic inhibitor

In this paper, the effect of adding different concentrations of kinetic inhibitors on the induction time of hydrogen sulfide hydrate formation in a reactor equipped with automatic adjustable temperature controller is studied. A novel method namely ＂sudden cooling＂ is used for performing the relevant measurements, in which the induction time of H2S hydrate in the presence/absence of PVP and L-tyrosine with different concentrations （100, 500, and 1000 ppm） is determined. As a result, PVP with the concentration of 1000 ppm in aqueous solution is detected as a more suitable material for increasing the induction time of H2S hydrate formation among the investigated kinetic hydrate inhibitors.

Mechanism of shales stabilization by hydrophobized poly(ethylene glycol)/K^(+) in water-base drilling fluids

The mechanism of the hydrophobized poly(ethylene glycol)(PEG)/K^(+) system inhibiting shale hydration was studied by laboratory experiment. The inhibition performance was evaluated through cuttings hot-rolling dispersion, bentonite inhibition and contact angle tests. The inhibition became stronger as contact angle and PEG concentration increased. A modified cuttings hot-rolling dispersion experiment suggested that these molecular systems did not act through the thermally activated mud emulsion(TAME) mechanism. The interaction of the PEG/K^(+) with clay samples was investigated through adsorption studies and by Fourier transform infrared spectroscopy(FT-IR), X-ray diffraction(XRD) and thermogravimetric analysis(TGA). The adsorption isotherms showed that the presence of K^(+) increased the PEG affinity for the clay surface. This inhibition effect was accompanied by a reduction of the bentonite hydration with PEG adsorption, evidenced by FT-IR, TGA and differential thermogravimetric(DTG) curves. XRD patterns were conclusive in showing that the presence of K^(+) ions limited the expansion of the clay interlamellar region to only one PEG layer, and the terminal hydrophobic segments of the PEG chains turned out to be determinant in enhancement of the inhibitory efficiency. The cuttings hot-rolling dispersion was carried out on water-base drilling fluid with PEG/K^(+), which proved the inhibition performance of PEG/K^(+) in oil field drilling.

Experimental and modeling study of kinetics for methane hydrate formation in a crude oil-in-water emulsion

A low-viscosity emulsion of crude oil in water can be believed to be the bulk of a flow regime in a pipeline.To differentiate which crude oil would and which would not counter the blockage of flow due to gas hydrate formation in flow channels,varying amount of crude oil in water emulsion without any other extraneous additives has undergone methane gas hydrate formation in an autoclave cell.Crude oil was able to thermodynamically inhibit the gas hydrate formation as observed from its hydrate stability zone.The normalized rate of hydrate formation in the emulsion has been calculated from an illustrative chemical affinity model,which showed a decrease in the methane consumption（decreased normalized rate constant） with an increase in the oil content in the emulsion.Fourier transform infrared spectroscopy（FTIR） of the emulsion and characteristic properties of the crude oil have been used to find the chemical component that could be pivotal in selfinhibitory characteristic of the crude oil collected from Ankleshwar,India,against a situation of clogged flow due to formation of gas hydrate and establish flow assurance.

A method for preventing hydrates from blocking flow during deep-water gas well testing

Based on the research of the formation mechanism and evolution rule of hydrate flow obstacle during deep-water gas well testing,a new method for the prevention of hydrate flow obstacle based on safety testing window is proposed by changing the previous idea of"preventing formation"to the idea of"allowing formation,preventing plugging".The results show that the effective inner diameter of the testing tubing and the wellhead pressure decrease gradually with the formation and precipitation of hydrates during deep-water gas well testing,and it presents three typical processes of slow,fast and sudden changes.There is a safety testing window during deep-water gas well testing.The safety testing window of deep-water gas well testing decreases first and then increases with the increase of gas production rate,and increases with the increase of hydrate inhibitor concentrations.In the case with different testing production rates,a reasonable testing order with alternate low and high gas production rates has been proposed to further reduce the dosage of hydrate inhibitor and even avoid the use of hydrate inhibitors considering the decomposition and fall-off of hydrates.Compared with the traditional methods,the new method based on safety testing window can reduce the dosage of hydrate inhibitor by more than 50%.

Effects of Low Concentration Methanol, PVP and PVCap on Structure-I Methane Hydrate Formation

Kinetic mechanisms describing how THIs （thermodynamic hydrate inhibitors） and KHIs （kinetic hydrate inhibitors） work on gas hydrate formation have drawn interests for decades. These mechanisms could be better revealed with more fundamental experimental studies. With experiments performed in an isochoric cell with continuous cooling and stirring, this paper presents observed effects of methanol, PVP （polyvinylpyrrolidone, Mw= 15,000） and PVCap （polyvinylcaprolactam, Mw = 6,000） on both nucleation and growth of structure-I methane hydrate at concentrations 100 to 3,000 ppm （i.e., 0.01 to 0.3 wt%）. The results suggest that methanol had no significant effect on nucleation, while it weakly promoted, spontaneous hydrate growth at an early stage. PVP and PVCap gave reduced average nucleation rate at and prior to hydrate onset, while increased the induction time and the degree of sub-cooling. PVP gave no observable effect on total gas intake and average hydrate growth rate. A decreased total gas intake was observed for all concentrations of PVCap.

High efficient development of green kinetic hydrate inhibitors via combined molecular dynamic simulation and experimental test approach

The development of environmental friendly low dose hydrate inhibitors like kinetic hydrate inhibitors(KHIs)is of great significance for the flow assurance in oil&gas production and transportation.In this work,a combined molecular dynamic simulation and experimental verification approach was adopted to increase the efficiency of KHIs development.The inhibition effect of a series of copolymers(N-vinylpyrrolidone and N-acrylate)on hydrate growth was studied by using both molecular dynamics simulation and experimental approaches.The simulation results demonstrated that introduction of hydrophobic ester and butyl group in PVP is beneficial for the inhibition.The length of the alkyl chain of ester group played an important role in improving inhibition performance.PVP-A,the one being introduced butyl ester group into PVP gets the best inhibition effect.In addition,inhibitors can restrict methane bubbles to re-dissolve into the liquid phase,thereby inhibiting the growth of methane hydrate.Increasing the interaction between KHIs and methane can also improve the inhibitory effect of KHIs.The experimental results confirm the reliability of the molecular dynamics simulation.

Synthesis and application of a novel combined kinetic hydrate inhibitor

In oil and gas exploration and transportation, low dosage hydrate inhibitors （LDHIs） are more favorably utilized to inhibit the formation of hydrates than thermodynamic inhibitors （THs） as a trend. However, there are no industrial products of LDHIs available domestically, and the corresponding application experience is in urgent need. In this paper, a combined hydrate inhibitor （HY-1） was synthesized after a series of reaction condition optimization, and its performance on THF hydrate inhibition was investigated using kinetic hydrate inhibitor evaluation apparatus with 6 cells bathing in air. The results show that when the reaction temperature is 60℃, the reaction time is 6 h, and the monomer： solvent ratio is 1：2, the product has the best kinetic hydrate inhibitor performance on THF hydrate. On these bases, the scale-up production of this combined hydrate inhibitor was carried out. Although the scale-up product （HY-10） performs less effectively on the THF hydrate inhibition than HY-1, it functions better than a commercial product （Inhibex501） during in-house tests. HY-10 was successfully applied to the gas production process. Field trials in northem Shaanxi PetroChina Changqing Oilfield Company （PCOC） show that 2 wt% of HY-10 is effective on natural gas hydrate inhibition. It is found through economic analysis that the use of HY-10 has obvious economi- cal advantage over methanol and Inhibex501.