Massive Annular Fracturing Practices in BJC Gas Field, Sichuan, China

Abstract Massive hydraulic fracturing has been successfully applied in tight gas reservoir development. Economic completion of tight gas sands with large hydraulic fracturing treatments requires cost effective and time saving operations. Traditional large fracturing jobs usually pump down 5.5" or 4.5" casing to meet the requirement of high pumping rate (30~55bpm). Post-frac snubbing operations are often needed to run tubing and clean out wellbores. Snubbing operations can be costly in terms of investment and time. Annular fracs have been applied in the industry as an alternative completion strategy. However, previously documented annular jobs are small size and range from 40k to 200k lbs of proppant pumped at relatively low injection rates of 15-25 BPM (3-4m3/min). This paper describes the practices of massive annular fracturing treatments down 5-1/2" by 2-3/8" annulus used at the Bajiaochang Gas field, Sichuan Basin, China, to replace fracturing down casing and subsequent snubbing operations. Three treatments have been performed since October 2005. The first job had to be terminated with 70% of the designed proppant (394k lbs) pumped because of the failure of the blast joint. Lessons learned were outlined and modifications were made to the blast joint and wellhead. Subsequent treatments were performed without mechanical failures with 350k and 282k lbs of proppant pumped at 30 to 35 bpm injection rates. The completion cycle time was reduced about 20% with substantial savings of up to $260k in well completion costs. Improved monitoring of BHP from static tubing for 3D fracturing modeling and effective treatment evaluation were also a benefit. This data has aided fracture design in highly complex fracture stimulation applications. Additional advantages also include: easily circulating out proppant if screen outs occur and more efficient flowing back for lower rate wells.