低孔低渗碎屑岩储层流体性质测井识别技术——以四川盆地安岳气田须家河组气藏为例

Logging identification of fluid properties in low porosity and low permeability clastic reservoirs: A case study of Xujiahe Fm gas reservoirs in the Anyue Gas Field,Sichuan Basin

四川盆地上三叠统须家河组二段是安岳气田的主要产气层段。由于该储层非均质性强、孔隙结构复杂,属于低孔、低渗—特低渗、高含束缚水饱和度储层,加之受到构造、岩性的影响,气水分异程度差,气层、气水同层,水层的测井响应特征差异不明显,致使储层流体性质识别难度大,试气成功率较低。针对这一现状,利用测井、试气等资料,结合须家河组储层特点,系统地分析了储层气水测井响应特征;采用饱和度重叠法、电阻率—孔隙度交会法、侧向—感应电阻率比值法、纵横波速度比法,从不同角度反映储层物性和气、水、干层之间的差异,综合判别安岳气田须二段的储层性质。通过对2011—2012年的新井跟踪对比分析,最终优选出以饱和度重叠法、电阻率—孔隙度交会法为主的流体性质判别技术,在对该区46层的储层流体性质识别中,测井解释符合率由60%提高到了83%,试气成功率也明显提高。该套技术适用性强,具可操作性,对川中地区其他区块也具有很好的指导作用。

The 2^nd member of the Upper Triassic Xujiahe Fm in the Sichuan Basin is the major pay zone in the Anyue Gas Field. The reservoirs in this member are characterized by strong heterogeneity, complex pore structure, low porosity, low to ultra-low permea bility, and high irreducible water saturation. In addition, these reservoirs are strongly influenced by tectonic structures and litholog ical facies, the degree of differentiation of gas and water is rather low, the differences in the logging responses of gas layers, interme diate gas-water layers and water layers are ambiguous. Therefore, the identification of fluid types is challenging and the success ratio of formation test is low. In this paper, logging data and formation test data in combination with the characteristics of the Xujiahe Fm reservoirs are used to systematically analyze the logging responses of the gas and water in the reservoirs. Various methods, such as the saturation superposition method, the resistivity porosity cross＋plotting method, the lateral-induction resistivity ratio method, and the compressional-shear wave velocity ratio method are used to identify reservoir properties and reveal the differences between gas, water and dry layers, so as to comprehensively determine the properties of reservoirs in the 2nd member of Xujiahe Fm in the Anyue field. Through tracking and analyzing the new wells drilled during 2011 - 2012, the saturation superimposition and resistivity-porosity cross-plotting methods were finally selected as the major technologies for the discrimination of fluid types. They were applied to i dentify fluid types of 46 layers. The coincidence rate of logging interpretation was raised from 60% to 83%, and the success ratio of formation test was also improved significantly. These technologies have strong applicability and operability, and can be applied in other blocks in the Middle Sichuan Basin.