1. According to field data, extra-heavy oil recovery through cyclic steam stimulation shows these features: cyclic oil production and oil-steam ratio changes like parabola; peak production appears in the third and fourth cycles;
Xinglongtai reservoir of Shuguang oilfield is the largest extra-heavy oil field in China at present, structurally located in middle part of west slope in western sag of Liaohe depression, with proved oil-bearing area of 5.9 km2, proved OOIP of 57 220 000 t. Since commercial production from 1997, the oilfield has constructed a productivity scale of 1 200 000 t/a.
According to characteristics of the reservoir, some new technologies and methods have been successfully applied in the pilot test, such as reasonable optimization of steam injection parameters, dual-fracture technology, dense perforation technology and steam fracturing technology. These critical technologies and methods allow the production rate, the cumulative oil-steam ratio and ultimate recovery factor of the shallow-thin and extra-heavy oil by steam flooding process to reach 17.4%, 0.21 and 37.7%, respectively.
A 67.5% viscosity reduction of the extra heavy oil has been obtained in the reaction carried out at 240 ℃ for 36h, while the material ratio (extra heavy oil to catalyst to water) is 100 to 0.04 to 8. The content of heavier fractions and sulfur decreases and the content of lighter fractions increases.
Based on flow state and commercial developing potential of crude oil in the formation and analysises of 255 heavy oil samples from 17 heavy oil blocks of 5 oil fields, taking the viscosity of degassed crude under formation temperature as the main index, and the density of dead oil as the secondary index, heavy oils are classified into four types, such as conventional heavy oil, heavy oil, extra heavy oil and super heavy oil.