Kinetics Study of Iron Sulfide Scale Dissolution

Abstract

Iron Sulfide deposition in production facilities is one of the flow assurance issues in oil and gas industry. It can cause tubing blockage, interfere well intervention, and reduce production in both sour oil and gas wells. Mechanical descaling is currently applied, but it is time consuming and costly. Dissolvers based on concentrated hydrochloric (HCl) acid have high dissolving power, but with a limited applicability due to overwhelming drawbacks such as corrosion and H2S generation. Low corrosive, non-acid chemical dissolvers were developed. However, the dissolution rate is low and is not comparable to concentrated hydrochloric (HCl) acid performance. Following the development of the iron sulfide dissolver presented in ADIPEC 2017, this work focuses on the improvement of the kinetics of iron sulfide dissolution, the kinetic factors of the dissolution rate. The non-acidic iron sulfide dissolver was used in lab dissolution tests. The effect of dissolution temperature, particle size, agitation, and ratio of volume of dissolver and mass of scale, were studied. Scale dissolution tests at temperature between 40°C and 125°C were carried out to evaluate the dissolution rate of pyrrhotite scale particles of sizes between 10 and 80 mesh. The ratios of volume (ml) of dissolver and scale particles (gram) were tested from 10:2 to 20:1. The agitation was from static to 160 rpm. The tests lasted for 6 hours. The dissolving amount was calculated by weight difference between the initial and final solids. The results show that the kinetics of pyrrhotite dissolution can improve significantly at high temperature due to the increase in the thermodynamic of dissolution, and by reducing the particle size to increase the contact surface area of scale particles. The increase of volume ratio of dissolver with the mass of scale particles and increasing agitation have limited effect on the kinetics of scale dissolution under the test conditions. This study provides and ranks the kinetic factors for iron sulfide dissolution. It gives a guideline to improve iron sulfide dissolution during field application using non-acid based iron sulfide scale dissolver.

Barium Sulfate Scale Removal at Low-Temperature

“…The solubility test is commonly studied to report the dissolution efficiency of the developed chemical dissolver for the scale sample by calculating the weight decrease of the scale before and after the exposure to the developed dissolver. The test was conducted several times to determine the optimum scale mass to dissolver volume ratio for the assessment of the economic and technical aspects [19,47]. The high efficient dissolver should provide a high dissolution rate with lesser dissolver volume 5.…”

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

“…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.…”

“…The test determines the fluid dissolution rate in terms of a mass unit of scale per volume unit of the fluid under the required temperature, pressure, operation condition if static or dynamic. The scale mass to removal solution liquid ratio is considered a critical parameter for the technical and economic design for the field descale job. , The scale precipitations mass was calculated from the diameter dimension reduction because of the scale and its density. , The main objective of the descaling operation is to achieve a higher dissolution rate with less dissolver amount for cost-saving . The static solubility test was performed as follows: A quantity of 100 mL of the fluid was put in a flask to be heated to 70 °C for 1 h with the hot plate as in Figure . A mass of 10 g from the scale sample (W1) was obtained. The scale mass was then added to the dissolver fluid in the flask. The test was continued for 6 h under 70 °C and atmospheric pressure. After the test period, the solution was left to cool down. After cooling down, a filter paper with a vacuum pump setup was used to separate the nondissolved scale solids from the solution. The weight of the dry filter paper (W2) was determined. The filter paper with the nondissolved scale solids was dried in an oven (70 °C) for 2 h. The weight of the filter paper with the scale solids after drying (W3) was measured. The weight of the nondissolved scale solids = W3 – W2 = W4 was determined. The dissolution efficiency of the scale dissolver = [(W1 – W4)/W1] × 100 was determined. …”

A Novel Low-Temperature Non-Corrosive Sulfate/Sulfide Scale Dissolver

“…However, the solid to liquid ratio was 2.0 g from the fine-scale to 20 mL from the new scale dissolver. The solid to liquid ratio is considered an important factor in the solubility design [21,48]. The solid amount represents how much of the scale was deposited and plugged the internal pipeline capacity for the fluid flow.…”