Case Study—Calcium-Carbonate-Scale Inhibitor Performance Degradation Because of H2S-Scavenger Injection in Semoga Field
Semoga field is an oil field in the Rimau block, which is located in South Sumatra, Indonesia. There is also a nearby oil field, Kaji field, in this block. These fields experienced reservoir souring and suffered a history of calcium-carbonate (CaCO3) -scale cases before a proper scale-inhibition program was implemented. At the end of January 2011, there was a separation-system problem at free water knock-out (FWKO) #2 Semoga Station. FWKO outlet lines were dismantled for inspection purposes, and it was found that the oil-outlet line at the downstream of the level control valve (LCV) was clogged by deposits, leaving an inner diameter (ID) of only 0.5 in.
X-ray defraction (XRD) and X-ray fluorescence (XRF) analyses confirm that the deposit is CaCO3 scale, even though routine scale-coupon monitoring shows very low scale growth. There is a hydrogen sulfide (H2S) scavenger Brand X injection at the downstream of the LCV on the FWKO #2, with a concentration of 11,050 ppm. The scale-inhibitor dosage in the water line on Semoga Station was only 9–10 ppm. Laboratory simulation shows that H2S scavenger Brand X injection reduced the scale-inhibition percentage from 97.2 to 35.3%, with 9 ppm of scale inhibitor. Meanwhile, no deposits were found in the oil-outlet line at the downstream of the LCV at Kaji Station, which has the same H2S-scavenger-injection point and dosage. The scale-inhibitor dosage in the water line at Kaji Station was 17.5–22 ppm. Laboratory simulation shows that 20 ppm of scale inhibitor resulted in a scale-inhibition percentage of 58%. Laboratory analysis shows that the scale-inhibition percentage increases linearly as the scale inhibitor increases under H2S scavenger Brand X influence.
However, another laboratory test conducted using H2S scavenger Brand Y shows that the scale-inhibition percentage will decrease with the increase of scale-inhibitor concentration, until it reaches the lowest value before increasing again with the increase of scale-inhibitor concentration. Thus, the scale-inhibitor performance under H2S scavenger Brand Y influence behaves parabolically.
It is concluded that H2S-scavenger injection increases system pH, resulting in the increase of scaling tendency. However, adding scale-inhibitor concentration is not always the answer to overcoming scale growth resulting from this effect. It is important to understand scale-inhibitor performance behavior on certain H2S-scavenger brands before taking preventive measures. Scale-inhibitor performance might have a linear correlation between increasing concentration and scale-inhibition percentage, as shown by the behavior with H2S scavenger Brand X, but it might also have a parabolic correlation, as shown by the behavior with H2S scavenger Brand Y or even other correlation types. A proper understanding of scale-inhibitor behavior can prevent a production loss caused by the deposition of 8,190 barrels of oil.
Petrofac Unit Wins $1.65-Billion Contracts for ADNOC’s Dalma Gas Project
Petrofac continues working relationship with UAE following contract awards for Dalma Gas Development project.
New Innovations Enable Autonomous Pipeline Inspections
As companies look to reduce the time it takes to inspect a subsea pipeline, as well as the costs involved in the operation, autonomous systems have become a more desirable option. How close are they to becoming the norm?
SPE Launches Flow Measurement Technical Section
Approved in October, the Flow Measurement Technical Section will help engage the greater SPE technical community in flow-measurement-related issues and technologies. It will cover the full spectrum of flow measurement, including single-phase and multiphase flow.
Don't miss out on the latest technology delivered to your email every two weeks. Sign up for the OGF newsletter. If you are not logged in, you will receive a confirmation email that you will need to click on to confirm you want to receive the newsletter.
05 February 2020
12 February 2020
07 February 2020
12 February 2020