基于物质平衡的页岩气井压裂改造裂缝体积与面积计算

页岩气井的压后排采过程呈现明显的阶段性特征，根据生产气液比与累积产气量的关系曲线可将整个排采阶段划分为早期阶段和晚期阶段。在排采生产早期，气井表现为气液同产，并以产液为主，此时页岩基质向裂缝系统的供气能力不足，整个水力裂缝系统（主压裂缝、次级压裂缝及沟通天然裂缝）可视为封闭体系。从物质平衡原理出发，建立了基于排采早期阶段生产数据的压裂裂缝初始体积和面积的计算模型，并以龙马溪组典型页岩气井进行了实例分析。结果显示，分析井的裂缝体积为注入压裂液量的70%左右，裂缝面积可达107m2量级，较大的改造裂缝面积也说明压裂形成了较复杂的缝网，提高了气井有效泄流面积。该模型解释结果与页岩气井排采参数和产气能力吻合良好，是评价压裂裂缝参数和改造效果的有效途径，对矿场水力压裂效果评估具有指导意义。

Estimation of fracture volume and its surface area on stimulated shale gas wells by material balance method

The flowback data of stimulated shale gas wellusually show different features along with well production process，and consequently the data may be divided into two stages: the early gas production stage (EGP) and late gas production stage (LGP) according to the changes ofgas water ratio(GWR).The early stage indicates a two-phase flow，and the water phase is the dominant because the gas supply of shale matrix to the fracture network is still insufficient.Also，in this stage，the whole fracture network (including primary fractures，secondary fractures and connected natural fractures) can be regarded as a closed system.This paper established a material balance model to estimate the stimulated fracture volume and surface area via the early stage flowback data，and the validity of this model was verified through two field cases of Longmaxi Formation shale gas wells.The results showed that fracture volume of the analyzed wells was about 70% of the total injected fluid volume，and the fracture surface area reached 107m2.Huge fracture surface area indicatedthat complex fracture network had beenformed during fracturing，which couldsignificantly increase the drainage area of the stimulated wells.The analyticalresults of this model agreed well with the flowback data and well production characteristics.It further demonstratesthat this approach is an effective method to evaluate the fracture parameters of stimulated wells，and is of significance to field evaluation of fractured shale gas wells.