The Research On The Separate Layer Fracturing Technology Applied In The41/2" Casing Well Of Changqing Oilfield

Chang6, one of the main producing formations in the ultra-low permeability reservoir in Huaqing Oilfield, contains several different small oil layers like Chang631, Chang632, and Chang633. The distribution of Chang631and Chang632is very stable, but Chang633exits only in some part of formations. However, all these layers have strong difference vertically and heterogeneity. And the typical features are low permeability, low pressure and low rate. To reduce the exploring cost, some blocks have been developed by means of large well-group and some wells have been completed with41/2"casing.According to Chang6’s features and special development methods, for example, some wells have adopted completion with41/2" casing and most wells are highly directional wells, to effectively exploit these wells which has several oil layers, based on the analysis of previous separate fracturing technologies which mainly contain sand-bridge separate fracturing and two-packer separate fracturing, the system research has been launched, which mainly includes separate fracturing conditions, fracturing ways, operating technology and related tools in the wells with41/2" casing. Then the separate fracturing technology has been formed in the41/2" casing wells and the fracturing string is composed of hydraulic anchors, K344packers and sand-blasters. Finally, considering the match between the inner diameter of41/2" casing and the inner diameter of fracturing string, to reduce the operating risk, the fracturing thread has been put forward:For the two-layer separate fracturing well, it is treated by fixed string, for the three-layer separate fracturing well, the first and the second layers will be operated by fixed string, and then the string will be tripped up to treat the last layer. Based on the previous field test, to insure the operated is done well, some important measures has been adopted, such as adjusting perforating parameters, optimizing the fracturing technology, modifying the sand blaster and packer.From2009to2010years, in the Huaqing Oilfield, there are113wells with41/2" casing treated by separate fracturing,96of which are applied by fixed two-layer separate fracturing string and17of which are treated by three-layer separate fracturing string. And95%of these wells are successfully treated; all the wells’string has been tripped out successfully after the fracturing operation. So the field application has shown that the separate fracturing technology is reliable, simple to operate, fast to operate and blow out. Now this separate fracturing technology has been the main fracturing technology for the development of large well-groups and41/2" casing wells in the ultra-low permeability reservoir.