页岩气井返排规律及控制参数优化

Flowback laws and control parameter optimization of shale gas wells

压后排液作为压裂和后期生产"衔上接下"的关键一环,页岩气井压裂后返排控制参数的选择及返排制度的制定还一直处于探索阶段,返排控制参数对页岩气井返排率及气井产量的影响尚不明确,返排关井时间、返排油嘴使用和更换基本都凭经验和固定模式。通过某区大量页岩气井返排数据分析,研究了返排速度、压裂+关井期间压裂液与页岩作用对返排率和气井产量的影响,明确了页岩气井压后返排作法,研究结果表明,提高返排率有利于提高页岩气井产能,但返排率不是决定气井产能高低的关键因素;页岩气井压裂施工结束后关井有利于人工裂缝的继续扩展,提高单井产量,但关井时间过长会引起大量的压裂液滞留于地层对储层造成伤害,反而降低气井产能;提出开井初期采用慢返排模式更有利于提高返排率和单井产能,采用对"油嘴进行控制、逐级放大、连续、平稳"的排液制度。页岩气井返排规律及控制参数优化结果为该区块页岩气井压后返排控制参数的优化提供了依据。

Postfrac flowback plays a key role in connecting the fracturing and the later production. At present, the selection of postfrac flowback control parameters of shale gas wells and the formulation of flowback mechanism are still in the exploratory stage, the effects of flowback control parameters on the flowback ratio and production rate of shale gas wells are not defined clearly, the shut in time of flowback and the utilization and replacement of flowback choke are basically based on experience and fixed models. Abundant flowback data of shale gas wells in one block were analyzed and the effects of flowback speed and action between fracturing fluid and shale during fracturing ＋ shut in on flowback ratio and production rate were studied. And accordingly, the flowback method after the killing of shale gas well was confirmed and the following conclusions were reached. First, the increase of flowback ratio makes contribution to the increase of shale gas well productivity, but flowback ratio is not the key factor controlling the numerical value of gas well productivity. Second, the shut in of shale gas well after the fracturing is favorable for the continuous propagation of hydraulic fractures and the increase of single well production, but if the shut in period is too long, a large amount of fracturing fluid will be detained in the reservoir, and consequently the reservoir is damaged and the productivity of gas well is decreased. It is pointed out that low speed flowback in the early stage of well startup is more favorable for the increase of flowback ratio and single well productivity. And it is recommended to adopt the flowback mechanism of ＂choke based control, gradual enlargement, continuity and smooth＂. The flowback laws and control parameter optimization results of shale gas wells provide the basis for the optimization of flowback control parameters after the fracturing of shale gas wells in this block.