Abstract
Ansai oilfield, located on the Loess Plateau in Northwest China, is famous for its typical low-permeability reservoirs and has been developed for more than 30 years. There are more and more flooded wells, low production wells and casing damage wells, which have become the "stumbling block" on the road of stable development. How to produce the remaining reserves more effectively? Sidetracking-fracturing in the original wellbore has become an important means to tap remaining reserves.
The recoverable reserves in this area are still large. The effectiveness of conventional stimulation measures in original wells is low, and there are new problems in drilling renewal wells. Due to the strict environmental protection regulations, the wellsite approved by local governments is limited and the cost of renewal wells is high. Developers tend to sidetrack and then fracture to restore production. There is no need to apply for new wellsites. Original wellbores are not wasted and the cost of renewal wells is saved. More importantly, fracturing network can be reconstructed to fully utilize the remaining oil and improve EOR.
3.5" wellbores were sidetracked in 5.5" wellbores. The multistage fracturing in slim hole is implemented. Sidetracking technology rebuilds new wellbore and reconstructs underground well pattern, establishing a new wellbore system for fracturing. The fine fracturing is realized by fine depicting the distribution of remaining oil and optimizing the sidetracking well type. The sidetracking holes accurately pass through the remaining oil area not touched by the original wellbores, achieving a very good effect of increasing production, and the investment cost is low. Through the implementation of sidetracking-fracturing technology, old wells are revitalized and the EOR is continuously improved. Compared with other stimulation measures, the sidetracking-fracturing technology has more obvious ability to tap the remaining oil. The biggest highlight of this technology is to make full use of the upper wellbores of long-term shutdown wells and the original surface equipment to effectively utilize the uncontrolled oil reserves of the original wells without drilling new wells.
Since 2015, more than 300 wells have been implemented, and the success rate of production increase exceeds 90%. The sidetracking-fracturing technology overcomes the constraints of environmental protection regulations, investment, site and slim hole technology in Ansai Oilfield, realizes the economic and effective development of low-permeability reservoir, and successfully improves EOR.
