Adjustment well is used to improve the production and change the relationship between the injection and production wells. Slot is the most important limiting factor for adjustment wells. But because of the small design area for offshore oil and gas development platform, dedicated area for well slots becomes even smaller, eventually leading to reduction of the number of well slots. Taking S platform as an example, this article presents two layers of casing of φ3397mm and φ2245mm in diameter respectively, cutting technology was used in the large-sized slot with full annular cementing, and the twinhole-in-monobore was completed in the abandoned slot.