页岩气未开发区单井可采储量评估方法

Evaluation method of recoverable reserves of single well in undeveloped area of shale gas

页岩气作为非常规气藏,储量评估结果受地质特征和工程因素的双重影响。已开发区在产井的单井最终可采储量(EUR)通常根据产量递减规律直接评估。北美页岩气勘探开发实践表明,同一地质区带内,在相似的钻完井技术条件下,不同年度完钻井的单井最终可采储量的统计分布具有可重复性,其累积概率曲线通常服从对数正态分布。因此,可以选取生产时间较长、评估结果较为准确的在产井作为类比井,分析其单井最终可采储量的统计分布规律,用于类比评估未开发区单井最终可采储量。实际工作中,需要根据已开发区的非均质性(P10/P90),结合地质特征与工程因素的差异将在产井划分为不同区带,建立不同分区的单井最终可采储量概率统计分布图版,类比评估与在产井相邻的、钻完井技术条件相似的未开发区单井最终可采储量。未开发区单井最终可采储量取值方法包括Swanson法、P^法和修正系数法等,各种取值方法应用条件有差异,应根据勘探开发进展和认识程度合理选值,为项目决策提供可靠依据。

As an unconventional gas reservoir, the reserves assessment of shale gas are affected by both geological characteristics and engineering factors. The estimate ultimate recovery(EUR)of a single producing well in the developed zone is usually directly assessed based on the production decline law. The practices of shale gas exploration and development in North American show that within the same geological zone and under the similar technical conditions of well drilling and completion, the EUR of a single well completed in different years exhibits repeatable statistical distribution, and its cumulative probability curve usually follows lognormal distribution. Therefore, producing wells with long production time and more accurate evaluation results can be selected for analogical analysis, so as to further analyze the statistical distribution law of the single well EUR for the analogous evaluation of the single well EUR in the undeveloped area. In practice, it is necessary to divide the production wells into different plays based on the heterogeneity of the developed zone(P10/P90), taking into account the differences between geological characteristics and engineering factors, aiming to set up the chart of single well EUR probability statistical distribution in different zones and analogically evaluate single well EUR in an undeveloped area adjacent to a producing well when using the similar drilling and completion technology. The value taking methods of single well EUR in the undeveloped zone includes the Swanson method, P^ method, and correction coefficient method. The application conditions of various value taking methods are different, and values should be selected reasonably according to the progress of exploration and development and the degree of understanding, thus providing a reliable basis for project decision.