With the extension of exploration and development of hydrocarbon into deeper formations, hydraulic fracturing and acidizing in these formations has become more and more important. Fracturing and acidizing ultra-deep wells added more difficulties to the optimization design and the safety of operation due to factors such as high formation temperature, high pumping pressure, high reaction rate between the formation rock and acid. These factors also affect the screening of chemicals and formulation of the working fluids. This paper discusses the investigation and practice of fracturing and acidizing technology in ultra-deep water injection wells (5830 to 5910 m in depth, 140·) in DH Oil Field emphasizing in: a) prediction of pumping pressure and measures to reduce it; b) optimization design and treatment implementation; c) field results of the application of the technology in production and water injection wells.

Significant stimulation results in production and injection wells were obtained with the applications of the fracturing and acidizing technology in DH oil field. The daily total water injection rate in five wells was only 672m3/d, a rate of 2200 m3/d was obtained after the first fracturing and acidizing treatments in 1995, 3500 m3/d after the second fracturing and acidizing treatments in 1997. The increase ratio of injectivity was 5.6. The average oil production rate per well stabled at about 217 t/d, the production decline rate was almost zero. The PFL rose from 1810 m to 1275 m.

Field practice shows that with a full understanding of the characteristics of the formation and requirements for the stimulation technology, difficulties associated with ultra-deep well fracturing and acidizing can be resolved and good stimulation results can be obtained.

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