An Overview: Practice, Experience and Achievement of Polymer Flooding In Daqing Oilfield

摘要

Daqing oilfield was put into production in 1960. Excellent achievement is acquired. It has maintain the production of 5000×10~4 tons/year for 27 years and 5500×10~4 tons/year for 13 years. Main technologies adopted in Daqing oilfield include early-stage water flooding for pressure maintenance, separate-zone water injection and separate-zone production, division of series of development-zone, well infilling, chemical flooding and conventional stimulation measures such as hydraulic fracturing and acidizing. Research on polymer flooding was started in 1960s. This technology was widely put into industrialized application since 1996. Current proportion of production rate from polymer flooding is over 25%. Technology of polymer flooding experienced laboratory experiment, pilot field test, industrialized field test and industrialized application, successively. In this paper, practice, experience and achievement of polymer flooding in Daqing oilfield were elaborated in view of class I reservoirs, class II reservoirs and class III reservoirs respectively. When it comes to class I reservoir, its effective thickness of single layer is more than 3 meters and effective permeability is greater than 0.3. When it comes to class II reservoir, its effective thickness of single layer is between 1 meter and 3 meters and effective permeability is between 0.1 and 0.3. Daqing oilfield use HPAM as polymer usually. When it comes to class III reservoir, its effective thickness of single layer is less than 1 meter and effective permeability is lower than 0.1. Each types of reservoir were produced by polymer flooding in different period. Class I reservoir was put into production for polymer flooding at first stage. Concentration of polymer solution is 2000mg/L and relative molecular weight of polymer is 2.5×10~7. Polymer dosage is 1100 PV.mg/L and injection rate is 0.12 PV/a. Injection-production well spacing is between 200 meters and 250meters. Class II reservoir was put into production with polymer flooding at second stage. Concentration of polymer solution is 1000mg/L and relative molecular weight of polymer is between 1.2×10~7 and 1.6×10~7. Polymer dosage is 640PV.mg/L and injection rate is 0.14 PV/a. Injection-production well spacing is between 150meters and 175meters. Class III reservoir was put into production with polymer flooding at third stage. Concentration of polymer solution is between 800mg/L to 1000mg/L and relative molecular weight of polymer is 5×106. Polymer dosage is 570PV.mg/L and injection rate is 0.25 PV/a. Injection-production well spacing is between 100meters and 125meters. Each types of reservoir adopt five-spot polymer flooding well pattern. Perfect achievement from polymer flooding is acquired. Compared with water flooding, water cut is declined by 20% to the maximum, and recovery efficiency is increased by 10% for polymer flooding of class I reservoir. Water cut is declined by 11% to the maximum, and recovery efficiency is increased by 7.8% for polymer flooding of class II reservoir. Water cut is declined by 6% to the maximum, and recovery efficiency is increased by 5% for polymer flooding of class III reservoir. Daqing oilfield has accumulate lots of experience for polymer flooding in aspects of oil displacement mechanism, design of reservoir engineering program, adjustment of scheme, evaluation and prediction of technique indexes and distribution of remaining oil.