A Method for Predicting Formation Pressure during High Water Cut Stage

Formation pressure is a crucial evaluation index for the development of water-injected oil fields. In the process of oilfield development, the magnitude of formation pressure represents the level of energy in the formation. Excessive or insufficient formation energy can affect the development efficiency of oil fields. Therefore, how to quantitatively predict formation pressure is of great significance for oilfield development. Existing methods for determining formation pressure in water-injected oil fields consider only a single factor and neglect the changing patterns of oil field development. To more reasonably evaluate reservoir formation pressure, based on the principle of material balance and considering the changing patterns of oil field development, a prediction method for formation pressure is established. This method can provide formation pressure under different injection-production ratios and degrees of recovery. Research shows that: when the cumulative injection-production ratio remains constant and is always less than 1, as the degree of recovery increases, the formation pressure gradually decreases, and the smaller the cumulative injection-production ratio, the lower the formation pressure; when the cumulative injection-production ratio remains constant and is always greater than 1, as the degree of recovery increases, the formation pressure gradually increases; when the cumulative injection-production ratio is initially less than 1 but gradually increases later, the change pattern is related to the formation voidage. When the cumulative injection-production ratio is initially greater than 1 but gradually decreases later, the change pattern is related to the formation over-injection volume. This method has been applied in an offshore oil field, and the formation pressure at different development stages of the oil field has been calculated. Based on the current formation pressure, the development of the oil field has been guided, and good results have been achieved. This method has important guiding significance for the development of similar oil fields.