基于目标的多层疏松砂岩气藏动态储量评价方法研究-以涩北气田为例

Due to the influence of wells interference and sand caused by unconsolidated sandstone ,water influx, pressure-sensitive rock and layers interference caused by commingling, the pressure and output of single layer is changing with production, which increases the difficulty of the dynamic reserves evaluation. Traditional dynamic reserves evaluation model based on single-layer flow, static pressure data, the complex multi-parameter input and the pseudo-steady state flow conditions can not meet the needs of unconsolidated sandstone gas reservoir development. The rock physical parameter database can be established with Sebei gas field rock outcrop rock samples. The samples combination of two and three layers for single-well reservoir physical analog can be selected through the random function. The sequential Gaussian algorithm can be used to set up the random geological model with multiple implementations of multiwell and multilayer (4-9 layers).we can record pressure and output data of physical analog and numerical simulation. There are a lot of interrelated production influencing factors which can not be "stripping" . The project put forward the goal-based ideal which focused on the parameters associated with these influencing factors - namely gas well production ,instead of concerning the single influencing factor. Through a lot of production data observation, analysis and the mathematical description of the variation of production, a new dynamic reserves evaluation method for multilayer unconsolidated sandstone gas reservior can be established.

砂岩疏松引起的井间干扰、多层合采导致的层间干扰、气井出砂、岩石压力敏感、气井出水使得单层压力和产量动态变化，这增大了动态储量评价的难度。传统的基于单层渗流模型、静压力数据、复杂多参数输入、拟稳态渗流条件的动态储量评价方法不能满足此类气藏开发的需要。选取涩北气田岩石露头，测定物性参数，建立基础数据库；通过随机函数选取岩样组合开展单井两层和三层气藏非均质物理模拟，采用序贯高斯算法建立多井、多层（4-9层）、多个实现的随机地质模型和数值模拟研究；记录单层和合层的产量和压力变化数据。由于影响气井产量的因素多而相互关联，无法单独"剥离"，且单个因素与储量之间没有明显相关性，项目提出基于目标的解决理念，不关注单个因素对储量的影响程度，而将研究重点放在与这些影响因素都关联的目标参数-产气量。通过大量的数据观察、分析，拟采用数学方法描述产量变化规律，建立一种新的疏松砂岩气藏动态储量计算方法。

涩北气田属于典型的多层疏松砂岩气藏。砂岩疏松引起的井间干扰和气井出砂、多层合采导致的层间干扰使得单层压力和产量动态变化使得各单层压力和产量呈现动态变化，给涩北气田的动态储量评价和长期稳产带来挑战。本项目以涩北气田为依托，开展物理模拟和数值模拟研究，揭示了多层气藏合采时的产量变化规律，进一步探讨了多层疏松砂岩气藏的动态储量评价方法。模拟表明：多层气藏合采时，气井的生产呈现动态变化，表现出层间自动接替的特征；渗透率差异较大的气层合采时，高低渗层的产气贡献率不同，开采初期由高渗层主导气井产气，稳产结束后由低渗层主导产气；渗透率级差增大会加剧高低渗层间供气能力的差异；气井压裂能加快早期产气速度，弱化纵向非均质性的影响；不同压力气层合采时具有明显的干扰现象，且易发生”倒灌”；初始压力不同会加剧渗透率级差的影响，使前期高低渗层间的产量差异加剧；层间窜流时，低渗层流体通过高渗层产出，低渗层基本不产气，可将高低渗层看作统一的压力传播系统。Arps产量递减法和物质平衡法在多层疏松砂岩气藏的动态储量评价中是适用的。造成涩北气田储量动用比低的原因主要有：拟合数据选取不当，忽略部分储层的动用储量；井底压力求取不准确；层间压差较大，发生井筒窜流。采取不同的拟合方式，相对高渗层和相对低渗层的拟合曲线出现上凸和下凹现象，与现场情况一致。基于此，针对多层疏松砂岩气藏动态储量评价问题，提出了一套评价思路。