基于概率法的页岩气单井最终可采量评估——以焦石坝页岩气田加密井为例

Shale gas EUR estimation based on a probability method:a case study of infill wells in Jiaoshiba shale gas field

页岩储层大面积连续分布的地质特征和“工厂化”作业的工程特性,使得同一区域内页岩气单井最终可采量(Estimated Ultimate Reserve,EUR)的统计分布具有可重复性,是概率法计算EUR的基础。常规确定性方法只能给出一个储量值,概率法能够计算储量的概率分布。四川盆地焦石坝页岩气田一期工程采用600 m井距开发,井间动用程度不高;为了提高气藏采收率,开展了焦石坝加密井网调整。采用概率法对加密调整方案的最终可采量进行计算,通过对焦石坝一期产建区页岩气井的地质、工程及试气情况的分析,筛选合适的类比井组,建立类比井组的EUR概率分布;借助蒙特卡洛算法,生成加密井网内页岩气平均单井EUR的概率分布,确定不同概率下的储量大小;借鉴类比井组动态储量评估参数,确定了加密井网内不同水平段长度页岩气井的典型井曲线。采用概率法实现了焦石坝气田加密井网内生产动态和最终可采量的预测,可为下一步开发方案部署和投资安排提供科学决策依据。

The characteristics of shale gas reservoirs and the engineering characteristics of“factory”operation lead to repeated production performance among wells,which is the theoretical basis of a probability method to calculate estimated ultimate recovery(EUR).Compared to the conventional deterministic method,the probability method can calculate a reserve probability distribution.The well spacing of the Jiaoshiba shale gas field in the Sichuan Basin is 600 m,leading to low production extent.Infill wells have been introduced in order to improve gas recovery.In this paper,a probability method was adopted to calculate the EUR for the infill adjustment.Suitable analogy wells were selected by taking geological characteristics,engineering conditions,testing data and well locations into consideration.Based on the EUR probability distribution of analogy wells,the EUR probability curves of infill wells were calculated with the MonteCarlo method.Typical well curves were established by analyzing the decline parameters of analogy wells.Future production performance and EUR of new wells or undrilled wells can be estimated with this probability method,which is the basis for future strategic decisions.