Maxi oilfield – a deep seated reservoir, located in the central part of North Dagang structural belt of Huanghua Depression, Is an Integrated dome anticline with major axis extending in a NE direction, being steep in the north and gentle in the south. The structure covers an area of 11 square kilometers with a vertical closure of 130 meters. The main pay zones are Ban II and III, T1 of paleogene, being a suite of bar sand and beach sand deposits of deep littoral facies. The depth of burial of the reservoir is 4,000 meters with relatively poor physical properties. The porosity is 13.3% and permeability is 13.6 md. It is of argillaceous cementation with a fair sorting. Rock compaction and secondary growth are obvious.
The distribution of oil, gas and water are mainly controlled by the structure. The oil-water contact is quite clear, being 3,900 meters in Ban II and 3,970 meters in Ban III. The crude property is good with low specific gravity of stock tank crude (with an average value of 0.8408) and low viscosity (6.2 cp/50°C on an average). The asphaltene content is low (4.98 percent on an average). The reservoir temperature is high (149°C). The presssure coefficient is also high (1.473/10m) with a large pressure difference between reservoir and saturation pressure (186 atm.). The underground viscosity of crude is abnormally low (0.38 cp). Therefore, it is a structural reservoir with an abnormally high pressure, low permeability and is undersaturation.
Exploration of this field began in 1965. In 1978, commercial oil flow was encountered and put into development with a 500m 5-spot well pattern in 1980. By the end of 1981, it was put on stream. Its recovery rate has been kept high during the four-year period of production. A series of development techniques have been used for deep-seated reservoir, such as protection of the reservoir from mud contamination, through tubing perforation under negative pressure differential, water injection under high pressure (400 atm), development through separated technique, deep pentrated fracturing, and a closed oil and gas gathering and transportation system, etc. thus achieving good oilfield development results. There were 21 oil wells and 5 injection wells by the end of 1984. The daily production was 473 tons and cumulative production reached 780,000 tons. The overall water cut was 6.5%. Daily injection of water was 613 m3 in five injection wells and the cumulative water injected reached 721,000 m3. The production capacity of oil wells was quite good and waterflooding was carried out normally.