It is estimated that tight oil takes up 46% of the total reserve volume, including conventional tight oil, super-tight oil and ultra-tight oil whose viscosity is 5.8×104mPa·s (degassed crude oil at 50°C). Some tight oil resources are 600-900m deep, while others are found in deep formations (1300-1700m). In order to deal with sand production and low recovery rate integrated researches on super-tight and ultra-tight oil buried in deep formations have been accomplished.
A group of 7 wells were selected and the overall steam stimulation was simulated by software. All modified chemicals such as the high temperature frothers, high temperature gel particle plugging agents and special resins were tested in labs in order to prove their performance, while downhole tools had been applied in adjacent wells. At last the average sweep efficiency and oil production rate of wells in the group were compared with that of adjacent wells.
Casing programs, horizontal sidetracking technologies and slim hole cementation technologies shall be optimized to extend the well's life. The multi-well steam stimulation technology which depends on injecting steam into a group of wells and creating a uniform temperature field is useful, as steam channeling caused by longitudinal heterogeneity in the tight oil reservoir and repetitive steam injection may be overcome. Mechanical interval selection technology and vacuum heat insulation pipe are recommended to obtain steam of appropriate volumes. Various high temperature frothers and gel particle plugging agents shall be applied to adjust the steam injection and production profile, improving the sweep efficiency. Liquefied carbon dioxide and other cleanup additives may be injected before steam as more water comes out and remaining oil keeps farther away from the borehole after repetitive steam huff and puff. Fracturing and sand exclusion may be achieved at the same time by squeezing special resins into formation while fracturing. Sand may be controlled by artificial boreholes, optimized liners and flushing foams. Series of drilling and production technologies have been optimized, therefore the average sweep efficiency and recovery rate of single wells in the group were improved by 12.52% and 13.23% respectively.
Conventional steam stimulation used to be adopted by scale in Block CH, while the daily production rate began dramatically decreasing after 4 to 5 rounds of steam injection. The integration of multi-well steam stimulation technology, mechanical interval selection technology, vacuum heat insulation pipe running technique and optimization of chemicals and gases improves heat utilization and sweep efficiency. While the optimized drilling and completion technology improved the quality of horizontal wells.