Successful Advanced Foam Slug Injection to Inhibit Bottom Hot-Water Condensate Zone Channeling in First Horizontal Well Steam Flooding Pilot, Bohai Bay, China

Abstract

Abstract Nitrogen-foam was usually used in late steam breakthrough stage to modify channeling profile. It was demonstrated that a special hot-water condensate zone developed at the reservoir bottom due to vertical radial flow during horizontal well steam flooding. And the poor stability of hot-water condensate zone front affected the expansion of steam chamber at the reservoir top. The risk of channeling was higher in early thermal connection stage for horizontal well steam flooding. It was showed that the higher the oil saturation, the smaller the foam resistance factor, but the foam can still be generated in the presence of oil, especially at the steam front with high water saturation. Based on indoor physical model experiments and reservoir numerical simulation method, a development technology for foam profile control was proposed during the early thermal connection stage. It was then carried out in field pilot 3 years ago. Results showed optimal time for starting foam injection was water cut reaching 40%-60%. The recommended foam concentration was 1.5%, and slug size was 0.10PV. Under this strategy guidance, the steam-foam pilot test has been carried out for 3 years smoothly. Three foam slugs including 175 t foaming agent was injected with 62000 t steam during steam flooding pilot. During foam injection, slope of Hall curve increased, and resistance coefficient reached as high as 1.01∼1.34. The daily oil production of well group increased from 180 m3 to 250 m3. Meanwhile, water cut rising rate was only 3.9%, indicating the water cut increased very slowly. It was observed that foam played a significant profile control effect on the hot water condensate zone at the reservoir bottom. Also, inter-well connectivity direction changed gradually after each foam injection, and dominant steam flow direction increased from 2 to 4, which indicated steam chamber expanded more balanced. The wellhead pressure increased from 8.8 MPa to 9.2 MPa, only increasing 0.4 MPa, indicating there was no pressure building around injection well. This type of early foam profile injection did not affect the establishment of thermal communication between injection and production wells. Different from traditional vertical well steam flooding, the timing of adding nitrogen foams was advanced. It was demonstrated that foam can effectively prevent steam channelling under high oil saturation conditions, especially at the steam front with high water saturation.