川西致密气藏压裂液氮助排剂优化研究及应用

由于川西气藏具有低渗、致密.压力低的特点,在压裂施工中,通常导致压后返排困难,返排率较低,残留的压裂液不仅对裂缝导流能力造成一定的伤害,同时也会影响压后产量.采用液氮助排剂可以大幅度缩短排液时间,提高压后返排率,液氮量越大虽然返排能力越强,但这种增大不是线性的,液氮用量过大超过线性助排阶段时,过度提高液氮用量,大大增加施工成本.因此,对液氮用量和混气方法进行优化研究.通过对川西致密气藏启动压力的规律研究,结合液氮的最小返排干度,提出最小液氮用量的评价公式,为液氮最小用量的评价提供理论基础;按照进入地层中液体先后和滞留时间长短,提出混注氮气量按照泵注压裂液的次序线性递减或台阶性递减,到井壁缝口处降至零左右的施工过程优化措施.此优化方法和措施,在川西气藏9口井中的现场试验表明24 h内返排率均达到72%以上,反排效果显著、压裂后气井增产效果显著.

OPTIMIZED RESEARCH AND APPLICATION ON LIQUID NITROGEN AMOUNT AND MIXING GAS METHOD

Gas reservoir in west Sichuan is usually low-permeability,tight and low-pressure.This cause difficult flow-back and low ratio after conventional fracture.The residual fracture liquid will injure fracture conductivity certainly and affect fractured production.Liquid nitrogen cleanup can decrease flow-back time and increase flow-back ratio obviously.Considered economical factors we must seek a combination point between construction effect and economic benefit.Optimization liquid nitrogen amount and mixing gas method is researched in this paper.Field application is implemented in 9 wells in west Sichuan and the success ratio is 100% and the flowback efficiency achieved 72% in 24 hours,the stimulation effect is remarkable.The research and application on this technology offer a good clue for efficient development same type gas/oil reservoir and is deserved to extend and apply.