| Popis: |
The most challenging cementing problems that been encountered in KS gas field of Tarim oilfield in China occurred in the salt-gypsum formation having the thickness of about 1000~3000m and the maximum depth of 7000m above. In most cases, there are high pressure saltwater layers among the salt-gypsum formation with the highest pressure gradient of 2.60g/cm3. HPHT (130 MPa, 160 °C, BHST), ultra deep well and narrow safety density window with the density of about 0.07-0.12 g/cm3 brought huge problems which made the well cementing very hard to achieve good bonding quality, especially for production liner cementing. The qualification rate of cementing quality of the salt-gypsum formation section was only about 40% in 2013. The bad cement bonding quality was recognized as one of the main reasons for this issue, which was the one of the top headaches for the operator. To answer these challenges, the ultra-high strength toughness casing, casing running downhole simulating technology, salt-tolerant spacer fluid and high density cement slurry, and step by step pressurized casing annular cement until cement set have been developed and applied successfully. The qualification rate of cementing quality of the salt-gypsum Layer section increased to 78% in 2014. The successful application of these techniques improving cementing quality of the significant thick salt-gypsum formation under the extremely challenging downhole condition promoted the exploration and development of ultra-deep subsalt reservoirs in China. |
