Scale deposition is one of the most serious oilfield problems and is largely caused when two incompatible waters interact chemically, creating high concentrations of carbonate (calcium), sulphide (iron, zinc) and sulphate (calcium, barium, strontium). The formation and growth of scale can also occur in fluids that have become supersaturated either as a result of changes in their temperature, pressure or pH. If left unattended, this can create a harmful and difficult to remove coating on any system or tool eventually hindering and blocking fluid flow, reducing production rates and causing costly damage to equipment. In the worst-case scenario, the well may have to be abandoned.
Though common in oilfield applications due to the geochemical processes between injection water, water trapped in the rock and the rock itself, the complex composition of reservoir fluids makes scale difficult to control and potentially costly to eradicate.
ChampionX, a global leader in upstream and midstream oilfield chemical and technology solutions, was contracted in 2016 by Gazprom Neft Badra to examine significant scale build-up in the Badra oilfield located in the Wasit Province in Eastern Iraq. The company’s global centre of excellence for scale technology in Aberdeen, UK was tasked to evaluate and propose a solution to restore full efficiency.
Located in the Wasit Province in Eastern Iraq, the Badra oilfield started production in 2014 and had produced more than 115,000 barrels of oil per day during that time. During FEED and field start-up, the potential of scaling due to the different dissolved solids and high salinity of the produced oil and wash water was underestimated as a major concern. It had a low water cut and was therefore not assessed. Normally, productivity is ensured by handling scale deposits via removal or through prevention from the start-up with a scale inhibitor treatment, which is proven to prevent or reduce likely deposits.
As no scale inhibition program was instigated at the process plant at the start of production, a very aggressive and hard scale deposit had formed that could not be removed mechanically.
Generally, large and heavy scale deposits can accumulate and coat perforations, casing, production tubulars, valves, pumps, and downhole completion equipment, such as safety systems and gas lift mandrels. In this case and over a period of 2 years, internal scale deposition had formed on the interior and casing of the oil export booster pumps, which led to an incremental reduction in the pump’s efficiency.
Bespoke analysis and treatment
A project team from ChampionX, with support from Gazprom Neft Badra Chief Specialists Mikhail Ognev and Evgenii Sigida, visited the field and performed a site survey whereby the pump was isolated and opened up to remove a sample of the scale. This was taken from Iraq to the Bundrant Technical Center in Aberdeen for laboratory analysis and testing. The facility also boasts extended laboratories for corrosion, hydrates and analytical work.
Knowing the chemical nature of the scale is an important factor to the success of a dissolution process. The ability to diagnose the composition of scales can lead to significant optimisation of chemical cleaning procedures. This will enhance the overall decontamination results and minimise equipment downtime.
With the scale deposits from the oil export booster pump, ChampionX performed exploratory structural equation modelling (ESEM) and energy-dispersive x-ray (EDX) analyses to characterise the location of the abnormal deposits at the micrometer scale. This demonstrated that the predominant scale present in the field scale sample was calcium sulphate (CaSO4). Furthermore, small amounts of barium sulphate (BaSO4), barium strontium sulphate (Ba, SrSO4) and trace amounts of iron sulphide (FeS) were found.
It was vital that an appropriate mix of chemicals was formulated which would not have a detrimental impact on other materials, such as the seals, beading and gaskets, causing further issues.
Comprehensive, customised solution
Based on the results, ChampionX identified a bespoke treatment package consisting of a scale dissolver, KCl dissolver solvent, and 10% of a mutual solvent and oil film cleaner/dissolver enhancer. For example, as calcium sulphate scale is not directly soluble in hydrochloric acid, it is converted to an acid soluble form by soaking in a carbonate or organic solution. It is then treated with dilute hydrochloric acid to remove the scale.
This package was rigorously tested on the sample piece of scale to ascertain its behaviour when dealing with extreme heat, cyclical processes and pressure. In developing and testing the solution, the laboratory team mimicked conditions in the well to adequately and efficiently remove the deposits from the pump. Based on the dissolver testing results, the company issued a comprehensive treatment proposal to the customer.
The oil export booster pump was isolated to run the chemical treatment. A customised procedure was developed involving application and circulation, the optimum heat and pressure regime, soaking, mechanical cleaning and removal of the debris, and a fresh scale dissolver package activated. This process was successfully completed across eight cycles, successfully dissolving and eliminating scale from the interior and casing of the pump with minimal to no impact to the integrity of the pump itself. Following treatment, the oil booster pump’s production efficiency was restored to its original design pump operating parameters.
Scale eradication and management
Scale formation is a common problem in the oil and gas industry and there are various methodologies for its remediation and prevention, which have their own associated costs and challenges.
In this project, as the deposits on the pump were at a critical level, chemical treatment was applied. However, while this was successful, by the very nature of the combination of produced water and wash water, scale build-up would return, and efficiency issues recur. This could ultimately mean either repeating the chemical process or replacing the damaged pump every 2 years, potentially costing more than USD1 million.
ChampionX, as well as treating the issues of scale build-up on the pump, also investigated the root cause of the problem and instigated a bespoke scale inhibitor program. This continues to be closely monitored to assure the long-term efficiency and performance of the operation.
Ali Abbas Nasser has 23 years’ experience in the petrochemical industry. The last 7 years have been spent in oilfield chemical application and management. He has participated in many local scientific conferences in Iraq and graduated from Basra University/College of Science/Chemistry Department in 1985. He Joined ChampionX in 2014 and is currently a service engineer working in the Badra oilfield, Iraq.
This article is based on 2016 testing and conclusions. Results may vary if a similar process was applied today. To learn more about ChampionX, visit www.championX.com.