Case Study: Effective and Economical Approach to Prevent Scale Formation Using Scale Inhibitor Squeeze into Reservoir

Abstract

Producing wells in Field T, Malaysia offshore have faced significant production impairment due to deposition of calcite and barite scale in the tubing and reservoir. A proactive approach is strategized to inhibit the scale formation along the inner wall of production tubing and reservoir through a scale inhibitor squeeze (SISQ) treatment with a lifespan of 2 years. The main objective of this approach is to eliminate the need of frequent stimulation jobs to maintain the production. Several attempts of scale inhibitor pumping in the past had been applied in the operator's production fields with different scale inhibitor (SI) formulations. However, some of the SISQ jobs were unsuccessful meanwhile some did not meet the treatment life targeted. A Root Cause Failure Analysis (RCFA) was conducted and the best practices and recommendations from the previous scale treatments were incorporated into this scale inhibitor squeeze treatment while the lessons learnt were implemented to prevent reoccurrence of unwanted events. In the past, most of the failed acidizing and SISQ jobs were caused by misdiagnosis of the root cause of production drop in wells, causing wrong selection of candidates right from the beginning. Another cause is the reaction between the chemical and existing scale in the tubing wall that resulted in the disintegration of the deposits, which subsequently block the flow of the well. There were also instances where coreflooding tests were not conducted due to unavailability of core samples. From the past failure contributors, the best practice proposed is to initiate any scale inhibition program by determining the correct root cause of production drop and to proceed with remedying the existing scale buildup. Examples of the solutions are through scale clean out, acidizing or workover before implementing a prevention solution such as SISQ. During the chemical selection stage, scale inhibitors should be selected based on a series of lab tests to study the performance of scale inhibitors, potential of damage formation, scale inhibitor retention core flood analysis, scale inhibitor thermal stability and fluids compatibility. Both wells B15 and D04 SS on which the SISQ jobs were conducted after acidizing job, have until now sustained their production. The MIC is well above 5 ppm target although approaching the end of 2-year treatment life. The Multifinger Imaging Tool (MIT) run downhole after one and a half years also indicated insignificant scale buildup on tubing wall. Permanent downhole gauge flowing pressure is also stable indicating no severe skin buildup. The produced water ions data, however, is insufficient to provide a view on the upward or downward trend of the scaling ions. In future replications, produced water ions sampling frequency should be increased.