The Effects of Suspended Solids and Fine Migration on the Design of Immiscible WAG Process in the Bokor Field

Abstract

Among the different Enhanced Oil Recovery methods being implemented in the matured fields of Malaysia,Immiscible Water Alternating Gas (iWAG) appears to be the most viable option. However, reduction in well injectivity and productivity would be very harmful to this process and render it ineffective. Therefore, extensive laboratory testing, interpretation and integration have been performed to reach the conclusions and recommendations presented in this paper.The target reservoirs in the Bokor are made up of unconsolidated and very heterogeneous rock with high permeability streaks. The mineralogy of the target reservoirs shows over 10% of clay, with abundance of kaolinites and illites which tend to cause fines migration and mixed layer illites/smectite which can swell. Therefore special handling of core samples is necessary for the laboratory testing; this includes flow through cleaning and critical point drying. The aim of the study is to establish the potential mechanisms of formation damage during the iWAG progress and determine preventive, mitigative measures and provide guidelines for treatment if damage occurs. The main focus is on formation damage by fines migration, dirty injection fluids (Mechanically induced damage)and clay swelling and de-flocculation (Chemical induced damage -fluid rock interaction) effect to Bokor field. The laboratory tests performed includes capillary suction time, filtration level test, critical velocity and fines stabilizer test, constant rate injectivity test and formation damage by iWAG injection test.Key areas of interesting findings include (1) Potential formation damage mechanism during the iWAG process (2) Strategies to prevent damage and improved injectivity, (3) Recommended treatment frequency based on injection half-life established in this study and (4) Field monitoring strategies.