Laboratory Technique for Screening Asphaltene Inhibitors for Kuwaiti Reservoirs

Abstract

Currently Kuwait Oil Company (KOC) is facing asphaltene deposition problems in the wellbore of some of the Marrat Jurassic reservoirs in West Kuwait (WK) and South East Kuwait (SEK). This has caused a reduction in production and shutting of some of the wells and a severe detrimental effect on the economics of oil recovery. This paper describes the results of the laboratory studies on the characterization and phase behavior studies of three different crude oil samples from Marrat reservoirs, and the screening of a number of commercially available inhibitors, which were proposed as a remedy and prevention of asphaltene deposition for this reservoir. Initially the samples were characterized for their chemical and physical properties. Then the phase diagram (P-T) and Asphaltene Deposition Envelope (ADE) for bottom-hole samples were established by measuring the saturation and Asphaltene Onset Pressures (AOP) at different temperatures from reservoir to surface conditions by using the laser technique Solid Detection System (SDS). Asphaltene Flock Point (AFP) analyses were then performed by the titration technique using Stock Tank Oil (STO) samples and n-Heptane as the asphaltene precipitant. The effects of different concentrations of each inhibitor on different reservoir fluids were investigated in the laboratory, using the AFP technique. The most efficient inhibitor with the optimized concentrations for each reservoir fluid was established for economical evaluation purposes. Based on these studies, a selected inhibitor is now being used for a pilot field study. Introduction Asphaltene precipitation and deposition from oil reservoir fluids during production is a serious problem as it can cause plugging of reservoir formation, wellbore, tubing and production facilities.

High Throughput Prescreening of Asphaltene Chemical Inhibitors Using Molecular Dynamics Approach

“…13 Recently, researchers used experimental techniques to select the most effective inhibitor for their target asphaltene and petroleum cases. For instance, Oskui et al 14 screened the efficiency of three commercial inhibitors (named A-C) on three oil samples using asphaltene flock point analysis (titration technique). They demonstrated that Inhibitor B was effective in a range of concentrations (0.1−5%) for two oil samples, while Inhibitor A was effective for the third oil sample.…”

Effect of Chemical Inhibitors on Asphaltene Precipitation and Morphology Using Ultra-Small-Angle X-ray Scattering

“…Asphaltenes are a solubility class of crude oil and are defined as the fraction of crude oil that is soluble in aromatic liquids (e.g., toluene) and insoluble in normal alkanes (e.g., n -heptane). , Changes in the temperature, pressure, or composition may reduce asphaltene solubility within crude oil and, consequently, cause deposition in subsea wells, pipelines, and porous formations, resulting in potential losses of millions of dollars . In particular, wellbore deposition causes drops in production rates, and excessive fouling may require complete shut-in of the well, resulting in losses of up to 50 000 bbl/day. , Furthermore, the mixing of incompatible oil in a refinery can lead to asphaltene fouling of heat exchangers and other equipment . To reduce the extent of asphaltene deposition, a variety of techniques have been commercially employed, which include monitoring of thermodynamic parameters within wells to avoid conditions where asphaltene precipitations is induced and the use of chemical inhibitors. ,,, A classical mechanism of chemical inhibition is that inhibitors adsorb on asphaltene molecules/aggregates and form a steric stabilization layer that promotes asphaltene dispersion within crude oil solution; however, extensive assessment of inhibitor mechanisms of action has not been reported in the literature.…”

“…In particular, wellbore deposition causes drops in production rates, and excessive fouling may require complete shut-in of the well, resulting in losses of up to 50 000 bbl/day. , Furthermore, the mixing of incompatible oil in a refinery can lead to asphaltene fouling of heat exchangers and other equipment . To reduce the extent of asphaltene deposition, a variety of techniques have been commercially employed, which include monitoring of thermodynamic parameters within wells to avoid conditions where asphaltene precipitations is induced and the use of chemical inhibitors. ,,, A classical mechanism of chemical inhibition is that inhibitors adsorb on asphaltene molecules/aggregates and form a steric stabilization layer that promotes asphaltene dispersion within crude oil solution; however, extensive assessment of inhibitor mechanisms of action has not been reported in the literature. Inhibitor action is also highly specific to a number of conditions: oil properties, concentration of inhibitor, temperature of operation, etc .…”

“…Asphaltene floc point (AFP) analysis is another class of inhibitor screening tests, , where C 7 is added stepwise to a crude oil–toluene–inhibitor solution, and changes in optical transmittance through the length of the sample are recorded as a function of C 7 added . Transmission increases initially as a result of the heptane dilution until asphaltenes precipitate and scatter/absorb light, defined as the floc point . Effective inhibitors are those compounds that shift the floc point to values of higher heptane concentration.…”

Dynamic Asphaltene Behavior for Gas-Injection Risk Analysis

“…The asphaltene onset pressure (AOP) is one of the most important factors in understanding asphaltene precipitating behavior. The solid detection system (SDS) based on light-scattering technique has been quite popular and widely used in all over the world (Kokal et al 2003(Kokal et al , 2004Jamaluddin et al 2000;Negahban et al 2005;Gholoum et al 2003;Garcia et al 2001;Oskui et al 2006;Gonzalez et al 2007) to measure AOP. The simple experiments to measure AOP are usually conducted using a mixture of reservoir fluid and injection gas, and various gas-mixing volumes are assumed to be investigated.…”