柴达木盆地东部石炭系古岩溶缝洞单元测井响应

柴达木盆地石炭系多发育致密化储层，后期成岩改造尤为重要。目前在盆地东部多口钻井中发现石炭系存在孔洞、溶缝以及溶蚀残丘等不同尺度的岩溶改造迹象，且个别钻井在该段有明显气测异常。因此，岩溶缝洞特征、缝洞测井响应是该区石炭系储层的基础问题。鉴于此，以柴东钻井资料为基础，岩石学-测井地球物理方法相结合，开展古岩溶缝洞单元测井响应研究。研究表明，石炭系岩溶缝洞可划分为风化壳型岩溶和沿构造断裂有关的岩溶缝洞两种类型。岩溶多见于克鲁克1~2段、扎布萨尕秀组以及怀头他拉与上覆层界限处。缝洞横向可对比，往往自然电位负异常，自然伽马中低值（20.5~35.0 API），声波时差异常增高，中子（13.9%）、密度（2.50 g/cm3）有一定镜像特征，电阻率（215.2~1100.0 Ω·m）低于围岩（>1100.0 Ω·m）。该区成熟的风化壳型岩溶缝洞在测井上表现为五个结构单元，上覆层、渣状层、溶洞层、裂隙-溶缝层、致密层。岩溶风化壳缝洞为该区主要岩溶缝洞类型，改造强度大于裂缝型，且共生。二者改造机制各异，但改造时间近似，推测为印支期的构造响应，时间持续到早中侏罗世甚至到早白垩世结束。 

Logging characterization of Carboniferous fracturedvuggy karst reservoirs in the eastern Qaidam Basin

Since the Carboniferous reservoirs are characterized by low porosity and permeability in the Qaidam Basin, the later diagenetic transformation is particularly important for oil and gas exploration. Karstification of different scales, such as pores, fractures, and dissolution residual mounds, have been found in the Carboniferous of many wells in the eastern Qaidam Basin. In addition, some well data shows obvious gas logging abnormalities in this section. Therefore, the characteristics and the logging response of fractures and caves are the necessary study issues for Carboniferous reservoirs in this area. Basing on petrology and the logging data, and the logging response of paleokarst fractures, the study shows that the Carboniferous karst fractures and caves can be divided into two types: structural faults related-type and weathering crust-type. The later one commonly develops in the first and second sections of the Keluke Formation, the Zhabusagaxiu Formation, and the boundary between the Huaitoutala Formation and the overlying formation. The horizontal comparison of the characteristics of the two types of karst fractures and caves shows that the value of natural potential is negative, the natural gamma is medium and low (20.5~35.0 API), the acoustic jet difference is abnormally increased, and the neutron (13.9%) and density (2.50 g/cm3) have mirror image feature, resistivity (215.2 Ω·m~1100.0 Ω·m) is lower than that of surrounding rock (>1100.0 Ω·m). The mature weathering crust-type karst reservoir could be classified into five structural units according to the logging curves, the overlying layer, paleosol layer, cave layer, fractured-vuggy layer, and tight layer. In general, the weathering crust-type karst reservoir was more dominant in the study area, with larger alteration intensity. However, these two types of reservoirs were also associated with each other in many cases. Except for their different alternation mechanisms, they shared similar timing in terms of their responses to tectonism, which was speculated to be from the Indosinian period to the Early Middle Jurassic and even the Early Cretaceous.