Abstract:
The Kuche Piedmont is an important oil production area of the Tarim oilfield. Well depths in this area are generally between 6,000 m and 7,000 m, and geological conditions are very complex. The maximum temperature encountered during drilling was 180℃ and the maximum gas reservoir pressure 150 MPa. Wells of five intervals were drilled to the Bashijiqike Formation, the target formation of only 200 m in thickness, and cased with liner string. In designing the thermal stability, rheology and mechanical property of the cement slurries, consideration has to be given to the challenges such as well depth, bottom hole temperatures (120-180℃), narrow clearance between borehole and the liner string, and the length of the liner string of only 200 m. Meanwhile, some of the wells were drilled with water base drilling fluids, leaving thick mud cakes on the borehole wall which were difficult to remove. This presented challenges to performing the cementing job with safety and high quality. To address these difficulties, cement slurries with high thermal stability and high strength as well as high temperature flushing spaces that are able to clean the mud cakes were selected for cementing the wells. A special cementing technique was engineered to use in combination with the cement slurries and spacers. Using this cementing technology, the efficiency of displacing annular space was greatly improved, and the strength of the cement slurries was developed quickly, which in turn improved the bonding quality of set cement and ensured the performing of late-stage channeling test at negative differential pressure. This technology has been applied in cementing the φ127 mm liner string in the well Dabei-1101, 97.2% of the cementing was qualified and 79.4% excellent. The cementing of the liner string passed the channeling test at 33 MPa negative differential pressure.
