川东北巴中地区须四段裂缝特征及有效性分析

Characteristics and Validity Analysis of Fractures in the 4th Member of Xujiahe Formation of Bazhong Area,Northeastern Sichuan Basin

巴中地区须四段储层属于低孔、低渗的致密砂岩储层,裂缝是改善储层物性和促进天然气富集的重要因素,开展裂缝方面的地质研究十分必要。基于钻录井、岩心、成像测井,测试等资料,对该区须四段裂缝特征及有效性进行了详细研究,取得了以下两点认识:1研究区须四段裂缝以构造缝为主,优势走向为NWW-SEE向(285°±15°),具有高陡倾角,充填程度较低。裂缝发育宽度较小,井上所识别的裂缝平均线密度较低,可能与高陡倾角裂缝的钻遇率低有关。裂缝的纵向分布不均匀,须四段上部裂缝发育程度高于下部,且局部存在裂缝发育密集段;2NWW-SEE向(285°±15°)且倾角大于45°的裂缝张开程度大,充填程度低,有效性好,对储层产量的提高有积极贡献,可作为研究区须四段重要的勘探目标。

The reservoir in the 4 th Member of Xujiahe Formation（ Xu4 member） of Bazhong area is characterized as tight sandstone reservoir with low porosity and low permeability,fracture is the important factor to improve reservoir property and promote gas accumulation. Therefore,it is very necessary to research on geologic characteristics of the fractures in Xu4 member. Based on drilling,logging,cores,imaging logging and test data. The characteristics and validity of fractures in the Xu4 member were studied and the following two conclusions were obtained： 1The fractures in the Xu4 member mainly belong to tectonic fractures and take the form of NWW-SEE（ 285° ± 15°）trending,high dip angle and low degree of filling. Meanwhile,statistics show that the fractures primarily have relatively small widths,the average line density of fractures identified on well is low,it is connected with the low drilling ratio of high dip angle fractures. The longitudinal distribution of fractures on well is uneven,the development degree of factures in the upper part of Xu4 member is higher than that in the lower part,and particularly,fractures are intensively developed in some places of the upper part. 2The factures with NWW-SEE（ 285° ± 15°） trending and dip angle above 45°have large opening degree,low filling degree. These fractures are evaluated as high effectiveness fractures,which have positive contribution to improvement of reservoir productivity. Therefore,they are the important targets of gas exploration in the Xu4 member of the study area.