4.- Problems in well cementing.
Well cementing technology presents failure sources that must be considered in order to decrease well construction process risks. The failure level of cementing technology is considered about 15%. The cementing process represents 8% of the well cost, however, if something fails during the cement job, it could increase to 20% and even the well may run a risk due to zonal isolation failure
The failure sources of cementing technology and their possible solutions have been described (1). There are three authors involve in the technology application in the real job, the cement manufacturer, the service company and the oil company, well and oil reserves owner.
The failure sources include the cement quality, slurry design, chemical additives, relationships between API tests and well conditions, tools calibration, technologies to determining well geometry and simulators available to design the cementing process.
As general rule, three basic aspects should have particular attention such as: both cement and service quality offer by service companies and simulators and expert systems that allow the cementing engineers the job planning, to follow and evaluate the cementing operation.
Some technologies using in well cementing have special risk of failure, for example if the cementing operation is running in the present sour gases (CO2 and H2S), generally present in petroleum reservoirs. Both gases inhibited the formation of convenient phases to avoid strength retrogression at high temperatures (2).
Failures in zonal isolation technology and new requirements in well construction operations support the necessity for checking the process, materials, tools, etc., used in cementing. In other words, it is necessary technological efforts that allow the petroleum industry to decrease the operation risk.
In other words, it is necessary technological efforts that allow the petroleum industry to decrease the operation risk. An important event happened on April 20, 2010, the platform that allowed construction to BP an offshore horizontal well in the Gulf of Mexico exploded (MC252 well, "BP's Macondo prospect"), killing 11 workers and started months of oil spill the Caribbean Sea. What went wrong in the construction of this well? (3, 4)
(1)“Failure sources in well Cementing Technology”, R.A. Bolívar, A. Centeno, V. Ciccola y W. Rodríguez, Visión Tecnológica, septiembre 2003, vol.10, n°2,169-190.
(2) “Effects of sour gases on oil well cements”, R.A. Bolívar C., M. E. Campos S. and C. Ramirez, Interciencia, 2008, vol.33, nº9, September, 1-9.
(3) A.Gonzalez, “BP alleges Halliburton destroyed test results on Deepwater Horizon cement”, World Oil, December 07, 2011, http://www.worldoil.com/BP_Halliburton_destroyed_test_results_on_Deepwater_Horizon_cement.html
(4) Deep Water, The Gulf Oil Disaster and the Future of Offshore Drilling Report to the President, National Commission on the BP Deepwater Horizon Oil Spill and Offshore Drilling, January 2011, http://www.gpo.gov/fdsys/pkg/GPO-OILCOMMISSION/content-detail.html
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