| The reserve of Dong Hetang oil field is mainly in CIIIO-6 formation which is strongly lack of homogeneity and has good permeability in the middle section, poor in both ends.In 2001, a period of moderate containing water, the water volume increased fast and it had heavy contradiction among layers which led to injection and production imbalanced and lower the production. Until 2008, it carried out a specific delamination to become two sets of straticulate exploitation, CIII1 and below of CIII2.They had good performance after water injection. The lower section achieved the requirement of design while the upper had poor result due to the difficulty of injecting water. Because CIII1 has abundant reserve up to 300×104t/km2, it is vital to launch gas injection test and feasibility study for gas drive analysis.This paper has a research on Dong Hetang oil field and the conclusions are below:(1) Flash Evaporation study on Dong Hetang oil field suggests that it has low gas-oil ratio, 15.1m3/m3, low dissolve gas volume and low bubbling pressure,6.549Mpa. The volumetric factor of crude oil is relativelv large of 1.904m3/m3 and the contractibilitv rate is low of 8.29% and the oil density is low. It shows this oil field had good quality which is suitable for gas drive to improve recovery ratio.(2) Phase state test of injecting associated gas indicates that the bubbling pressure was raised from 6.549Mpa to 40.261Mpa after injecting associated gas of 67.64%, which, however, was still lower than formation pressure. The gas-oil ratio had an increase from 15.10m3/m3 to 273.10m3/m3 but the density decreased to 0.6051g/cm3 from 0.7593g/cm3. The drop range of saturated oil was relatively huge. The bulk factor increased fast from 1.0904 to 1.8303 which had a big rise. The capability to dissolve associated gas had improved and the quality promoted.(3) Dry gas injection reveals that the bubbling pressure raised from 6.549Mpa to 44.037MPa w:hich was higher than formation pressure after injecting day gas of 67.64%. The gas-oil ratio had an increase from 15.10m3/m3 to 242.91m3 but the density decreased to 0.6276g/cm3 from 0.7593g/cm3. The drop range of saturated oil was relatively huge. The bulk factor increased fast from 1.0904 to 1.7103 which had a big rise. The capability to dissolve associated gas had improved and the quality promoted.(4) Thin tube test shows that in 900,000 m3/day natural gas processing station of Lunnan the minimum miscibility pressure of associated gas drive was 33.07MPa whicn was lower than formation pressure.It was belonging to miscible drive. The minimum miscibility pressure in 400,000 m3/day miscibility pressure natural gas processing station was 43.50MPa which was higher than formation pressure. It was immiscible drive.(5) Long core displacement experiment shows that continuous injection of Dong Hetang field can get higher recovery ratio. Comparison with different injection rates, the best efficiency reached 89% and 90% when the injection rate was 1.0ml/h and 7.5ml/h respectively. But when the injection rate was 7.5ml/h, gas channeling occurred which did not influence recovery ratio.When the rate was 3ml/hr or 5ml/hr, it also had a good recovery. In a nutshell,1ml/h is the best rate.(6) Based on experiment results,it analysis the potential of injection exploitation and chooses the suitable injection matter, injection and production method and keeps the formation pressure condition. |
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