基于岩心-电成像测井的裂缝定量表征方法——以库车坳陷ks2区块白垩系巴什基奇克组砂岩为例

Quantitative fracture evaluation method based on core-image logging: A case study of Cretaceous Bashijiqike Formation in ks2 well area, Kuqa depression, Tarim Basin, NW China

通过对大量岩心、成像测井等资料的对比分析,建立了砂岩构造裂缝的定量表征方法,对库车坳陷ks2区块白垩系巴什基奇克组裂缝＂点＂、＂线＂、＂面＂分布特征进行了研究。首先利用岩心校正相应深度的电成像测井裂缝参数,获得经验校正值,再对未取心段的电成像测井解释裂缝参数进行校正,最终得到目的层每米裂缝参数数据。研究发现,ks2区块巴什基奇克组裂缝主要为高角度构造缝,倾角主要为45°～75°,走向为近南北向和近东西向,单井裂缝线密度0.11～1.30条/m,面缝率0.027%～0.130%,平均宽度0.13～0.55 mm,长度0.39～1.20 m。依据裂缝线密度、面缝率数值,定量评价裂缝发育程度为Ⅰ类发育、Ⅱ类较发育、Ⅲ类欠发育3个级别。裂缝主要发育在巴一段、巴二段的砂岩中,形成具有较好连续性的4～6个裂缝段。裂缝参数、厚度、发育级别随至断裂、背斜轴部的距离增大呈指数减小,Ⅰ—Ⅱ类裂缝多分布在至断裂800 m、背斜轴部1 800 m范围内。据此,定量预测该区块裂缝平面分布发现,裂缝发育整体东部好于中西部、南部好于北部,ks201井、ks207—ks2-12井一带、ks203井周及断裂附近的裂缝线密度可达1条/m以上。

A quantitative evaluation method of fracture is established based on core observation and image logging, and is used to characterize the distribution feature of fractures in Bashijiqike Formation of ks2 well area. This method gets the empirical corrections of fracture parameters between cores and image logging in the same depth, and these empirical values will be used in other depth where cores are not acquired to obtain all the fracture parameters per meter of the target layer. The study shows the fractures in ks2 well area are mainly high angle structural fractures between 45°？75°, and their strikes are near SN or near EW. The fracture linear density values are 0.11？1.30/m, the fracture area ratio is 0.027%？0.130%, the average fracture width is 0.13？0.55 mm, and the fracture length is 0.39？1.20 m. The development of fracture is divided into three levels（Ⅰ-developed, Ⅱ- relatively developed, Ⅲ-poorly developed） based on the linear density value and surface area ratio. Fractures in this well area are most abundant in sandstones of 1st and 2nd members of Bashijiqike Formation, forming 4-6 fracture segments with good continuity. The thicknesses, development levels, parameters of fracture segments decrease exponentially with the increase of distance to fault and to anticline axis. The most favorable area（Ⅰ-Ⅱ） is within 800 m from the fault, or within 1 800 m from the anticlinal axis. It is predicted the fractures in ks2 well area, are more developed in the eastern area than the middle-western area, and more developed in the southern area than the northern area, and that the linear fracture density can be up to 1.0 /m around Well ks201, Well ks207-ks2-12, Well ks203 and areas near faults.