页岩气产量数据分析方法及产能预测

Production data analysis and productivity forecast of shale gas reservoir

关键词:  页岩  产量分析  典型曲线  产能预测  储量评价

Key words:  shale  production analysis  type curves  productivity forecast  reserves estimation

摘要:

基于页岩气井线性非稳态流动特点,运用双重孔隙线性瞬态流典型曲线分析Eagle Ford页岩气藏一口多级压裂水平井产量数据,并进行储量评价。根据产量与时间双对数曲线关系,将该气井生产分为表皮效应、线性流动、边界效应3个流动阶段;运用基质线性流动模型计算该气藏基质渗透率,利用数值模型对计算结果进行验证;根据边界效应时间点求取该井体积压裂范围游离气储量,在此基础上进行产能预测,并研究吸附气解吸对气井产量的影响。结果表明:该井体积压裂范围游离气储量与裂缝模拟结果符合度超过85％;解吸气对页岩气井产量贡献取决于平均地层压力与吸附曲线形态;解吸气对该页岩气藏开发早中期的影响可忽略,对开发后期产量的影响很大,气体解吸能增加总采出量30％以上。

Abstract:

Based on the linear unsteady-state flow behavior, the type curves with the assumption of double porosity transient linear flow were used to analyze the production data of one multi-stage fractured horizontal well in Eagle Ford shale gas reservoir, and the original gas in place(OGIP) was estimated. Three flow regimes were identified on log-log plot consisting of apparent skin effect, matrix linear flow and boundary dominated flow. The matrix permeability was estimated based on matrix linear flow regime, and the results were verified with numerical model. The OGIP was calculated based on the boundary dominated flow regime which represents the total free gas in stimulated reservoir volume region. Furthermore, the productivity forecast was carried out and the effect of desorption was investigated. The results show that the total free gas in stimulated reservoir volume region is close to the result from hydraulic fracturing modelling, and the error is less than 15％. The effect of desorption depends on the reservoir pressure and the shape of isotherm adsorption curve. In early time of this case, desorption is not effective. However, for long-term productivity forecast, it is necessary to account for this phenomenon by providing an accurate isotherm since gas desorption makes the estimated ultimate recovery increase over 30％.