Development and Qualification of New Zinc and Lead Sulphide Scale Inhibitors for Application under Harsh Conditions

Abstract

The paper will describe the challenges facing sulphide scale control in the challenging environment found in Totals Elgin and Franklin Fields. It will present the advances made in developing new thermally stable and compatible chemical inhibitors able to withstand the extreme conditions in these fields. The paper will then describe the test methodologies and experimental approach developed to examine the performance of various prototypes or candidate chemicals followed by more detailed testing on selected chemicals under the more challenging field representative conditions as well as application specific testing for both squeeze treatment and downhole continuous injection at temperatures of 196°C/282 °F. In collaboration with University of Lyon Total has developed a range of new inhibitor types specifically designed to inhibit sulphide scales and remain stable under the harsh conditions of these fields. The chemicals have been qualified independently using recently developed test methodologies for lead and zinc sulphide and show better performance against these unconventional scales comparing to the other chemistries examined. In addition, a new method was developed for scale inhibitor residual analysis. This method based on time resolved fluoroscopy allows a quick and very sensitive measurement. The work concludes that a new range of Zn/Pb sulphide specific chemicals have been developed for field application with selected species also being suitable for application under the extreme conditions of the Elgin and Franklin Fields. Zinc and lead sulphide scales became an increasing challenge in oil and gas production. More specifically when formed from wells producing under very severe conditions of high temperature (196°C/282 °F) and high salinity formation waters such as those experienced in Central Graben Fields, their prevention by conventional scale inhibitors has proved challenging. To date after extensive chemical qualification over several years, no conventional scale inhibitor has been found which can both inhibit lead and zinc sulphide and survive under the extreme conditions of these fields. Therefore, the results in this paper represent a significant advance in the ability to control sulphide scales and test the inhibition under appropriate conditions.

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

“… 11 Commonly, zinc and lead sulfides precipitated in downhole completion tools as control valves. 12 , 13 The drilling operations utilized barite (barium sulfate) as a weighting material for the drilling fluids, and during drilling operations, the mud invades the drilled formation with barite solids, and therefore, barium sulfate scale precipitated and damaged the drilled formation by reducing the rock porosity and permeability. 14 Strontium-based sulfate is a common scale with the production surface facilities and processing units.…”

“…Due to these controlling conditions for the scale precipitation, the location of scale is different based on the existing source and operation condition as the sulfate scales precipitated with the seawater injection system because of incompatibility of water sources and this is considered as a hard scale type due to its low solubility with acid . Commonly, zinc and lead sulfides precipitated in downhole completion tools as control valves. , The drilling operations utilized barite (barium sulfate) as a weighting material for the drilling fluids, and during drilling operations, the mud invades the drilled formation with barite solids, and therefore, barium sulfate scale precipitated and damaged the drilled formation by reducing the rock porosity and permeability . Strontium-based sulfate is a common scale with the production surface facilities and processing units .…”

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

“…The locations of scale depositions differ due to temperature and pressure conditions. Lead and zinc sulfide scales are found to be deposited in the shallower part of the well completion, control valves, and in the subsurface safety control valves [13,14]. Sulfate scales were found to be deposited by the seawater injection operations, and such a scale is one of the hardest scales to be removed as it has low acid-solubility.…”

Dissolution Kinetics of Different Inorganic Oilfield Scales in Green Formulations

“…Inorganic scales can form at any point of the production system including reservoir, near wellbore, production tubings, downhole pumps, and surface facilities . Technical problems associated with scale formation include but are not limited to fluid flow obstruction, heat transfer impedance, metal parts wearing, reduced equipment life, localized corrosion, reduced performance of corrosion inhibitor, and unanticipated equipment shutdown .…”

“…Inorganic scales can form at any point of the production system including reservoir, near wellbore, production tubings, downhole pumps, and surface facilities. 2 Technical problems associated with scale formation include but are not limited to fluid flow obstruction, heat transfer impedance, metal parts wearing, reduced equipment life, localized corrosion, reduced performance of corrosion inhibitor, and unanticipated equipment shutdown. 3 The common types of inorganic scales found in the oil field are carbonate scales such as calcite (CaCO 3 ) and siderite (FeCO 3 ) and sulfates such as barite (BaSO 4 ) and celestite (SrSO 4 ) in addition to sulfides like pyrite (FeS 2 ) and pyrrohtite (Fe 7 S 8 ).…”