Abstract:

Optimization of rational injection-production pressure system is a key part of developing water flooding oilfield.However, the methods widely used previously have certain disadvantages.The water-absorption and fluid productivity index method does not take into consideration factors such as the imbalance between injection and production fluids, density difference between oil and water, and their volume factors.The method of ‘water absorption and fluid productivity index and injection-production ratio’ignores density difference between oil and water and volume factor.The method of ‘index ratio of water-absorption to fluid-productivity and pressure difference between injection and production well’has no theoretical and practical significances.The method of‘considering single well and reservoir pressure variations pays no attention to the influences of start-up pressure of water injection well and start-up pressure of production well on oilfield development effects.To solve the above-mentioned problems, a new approach to optimize the injection-production pressure system in water flooding oilfield was proposed based on the pressure profile of injection-production.Compared with the previous ones, the new method is comprehensive, taking into account such factors as injection-production imbalance, density difference between oil and water, volume factor, start-up pressure gradient of injection wells and start-up pressure gradient of production wells.Experiments show that it can be applied to parameter calculation of all reservoir types and all reservoir pressure distributions in a water flooding oilfield.For example, it has been used to calculate the rational pressure system of injection-production of the No.1-3 sandstone reservoirs in the 2^nd Member of Shahejie Formation of Shengyi block, Shengtuo oilfield.And the result shows that the ratiional ratio of oil to water wells is 1.42, the rational formation pressure-keeping level is 17.29 MPa while the rational fluid-production volume and water-injection are 14 572.41 m³/d and 15 906.88 m³/d respectively, with 12 452.41 m³/d and 13566.88 m³/d more than before, and with a remarkable increase of fluid production and water injection.

Key words: reservoir pressure distribution, start-up pressure of injection wells, start-up pressure gradient of production wells, rational pressure system of injection-production, water flooding oilfield