Scale formation in the near-wellbore area, the tubing and in topsides facilities is one of the major challenges associated with oil production and so must be managed. The objective of scale management is to maximise value with respect to the risks to production from scale, balanced against the cost, downtime and potential damage from any treatment. Chemical treatments to mitigate against scale and to dissolve scale are frequently applied and costly. Shell U.K. Limited Production Chemistry has applied two methods in order reach the goal of an optimised scale management system. These are Environmental Scanning Electron Microscopy/Energy Dispersive X-Ray (ESEM/EDX) and Principal Component Analysis (PCA).
ESEM/EDX can be used to determine if scale is actually formed in the well or near wellbore area. Several wells in a Shell field showed a decline in barium figures and consequently were considered to produce in a scaling regime. ESEM/EDX analysis clearly showed that there was no scale formation in the well or near wellbore area, enabling continued production and avoiding shutting in these wells.
Single ion analysis is often not accurate enough to demonstrate what is happening downhole, e.g. if seawater breakthrough (SWB) has occurred or not. PCA is a powerful tool with which one can resolve subtle yet significant changes in produced water and thus predict injection water breakthrough earlier and with higher accuracy. PCA was used in one case to prove that there was seawater breakthrough occurring in a well, although the reservoir model did not support this and single ion analysis did not give a clear message. The subsequently undertaken scale dissolver and scale squeeze not only saved the well from scaling up, but also led to a significant production gain. In another case it was possible to calculate if SWB had occurred or not much more accurately. Before the statistical analysis the suspicion was that 18 wells had undergone SWB and subsequently were treated with scale squeezes. With this analytical technique the number of wells thought to have SWB was reduced from 18 to 3 with 3 more where SWB is expected soon. Due to this, the amount of scale squeezes in one campaign was reduced from 18 to 6.
Shell U.K Limited's operations in the North Sea have benefited considerably from the use of PCA and ESEM/EDX.