Abstract
The buried depths of reservoirs in North Buzachi oilfield range between 400~500m, but Its geologic structure is very complex due to the existence of shallow gas and aqueous layer within 20~160m and a HP gas layer at 300m(1.30–1.50 g/cm3). In addition, the reservoir is easy to leak for its high permeability and low fracture gradient (1.6g/cm3), and the ground temperature is −40□ in winter. All these factors bring great challenges for the cementing jobs here and often result in poor cementing quality such as shallow water & gas channeling from wellheads and serious leakage in reservoirs. 72 out of the 97 wells cemented during 1974~2000 were abandoned due to poor cementing jobs. Gas and water channeling were found from 15 wellheads that were cemented from 2003 to 2004. This paper focuses on how we develop a new cementing technology to improve the cementing quality in this oilfield. Based on the High Packing Theory, we developed the High Performance Low Temperature No-waiting & Low Density Cementing ™ technology(NLDC) whose slurry density can as low as 1.20g/cm3, which includes high performance cementing additives, superfine active mineral materials, Super-low temperature accelerator, and Anti-migration additive, etc. This technology are characterized by good anti-channeling & Anti-leakage & early strength development ability under the temperature 20~30□. Up to now, more than 300 wells have been cemented successfully with this technology, 97% of which are with excellent bonding quality. Those problems which have puzzled the North Buzachi for long have been radically solved, such as bad isolation, annular migration, shallow gas and water blowing off from wellheads and leakage during cementing. This NLDC cementing technology has been widely applied in North Buzachi oilfield for 5 years and also a good solution to shallow gas & water cementing and low pressure-easy-leakage formation cementing.
