应用生产数据进行气井重复压裂选井的方法

低渗透气藏气井压裂完井生产一段时间后，裂缝导流能力逐渐下降，往往需要重新进行压裂。现场一般把通过不稳定试井计算的表皮系数作为重复压裂选井参考指标。但目前由于天然气供不应求，为保证产量，气田很难进行大规模的关井压力恢复测试，无法得到气井的表皮系数，而且有些井做不稳定试井的时间较早，表皮系数已经发生变化，因此无法根据表皮系数的大小选井，导致重复压裂的效果不佳。而气井长期的生产历史数据包含了气藏动态的重要信息，文章利用定容气藏的物质平衡方程和产量递减曲线联合分析生产数据的方法，对达到拟稳态流动的气井通过拟合变流量和井底压力的生产数据，达到不关井测试计算表皮系数的目的。通过现场实例验证，根据此方法计算的表皮系数与重复压裂井施工的效果有明显的相关性。该方法简单实用，不但为下一步重复压裂选井提供了量化的参考指标，而且节约了大量的测试时间，具有明显的经济效益和推广价值。

METHOD OF SELECTING REFRACTURING WELLS BY PRODUCTION DATA ANALYSIS

The flow conductivity of fractured gas well in low-permeability gas reservoir will decline along production and needs to be restored by refracturing. In general, skin factor calculated by common transient well test is an important index for refracturing candidate. However, a well test is hard to be implemented and skin factors can not be obtained in a gas well because of gas loss, especially under current situation that gas demand exceeds supply, besides, the skin factors from earlier well tests could change largely after production for some time. Therefore, the selection of a gas well candidate can not be performed based on the skin factors, leading to unsuccessful refracturing generally. Fortunately, important information of gas reservoir performance may be reflected by a well with long-time history production data. It is presented a method based on declined-curve and material balance time to calculate skin factor with well production data, which can realize the calculation of a skin factor of a gas well with pseudosteady state flow at non-shut in test through matching the production data of variable flow rate and bottomhole pressure. The history cases in Jingbian gasfield show good consistency between the skin factor and refracturing results. The method has apparent economical benefit and practical application in the selection of refracturing wells.