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四川砂岩储层多为低孔、低渗的储层，易受污染。钻井液中的固相物质及地层中的粘土矿物遇到水膨胀，从而堵塞本已狭窄的孔喉等渗滤通道。为了减少钻井液对砂岩储层的污染，需对油气层采取一定的保护措施。欠平衡钻井是对砂岩储层进行保护的一种有效方法，相应地，也需要进行欠平衡带压测井等油气层保护措施。章对欠平衡状态下部分测井仪器的响应特征及测井资料受到的影响进行分析，主要考虑了深浅双侧向、补偿声波、补偿中子等资料的影响因素。根据对邛西3井的欠平衡测井过程及测井资料的异常现象进行分析，提出了控制资料质量的具体措施。在潼南1井欠平衡带压测井施工中也取得了好的效果。

Controlling the Quality of Underbalance Logging Data

The sandstone reservoirs in Sichuan Basin are mainly the ones with low porosity and low permeability and they are easy to be damaged.The narrowed pore-throat channels were plugged by the solid matters in drilling fluid and the water-swellable clay minerals in formation.In order to reduce the sandstone reservoir's being damaged by drilling fluid,it is necessary to provide some protective measures for the hydrocarbon reservoir.Underbalance drilling is one of the effective methods for protecting the sandstone reservoir and corresponding reservoir protection measures as underbalance logging are needful also.In underbalance circumstances,the response characteristics of partial logging instruments and the influence upon log data are analyzed and the influemce factors of the data on deep-shallow dual laterolog,compensated sonic log and compensated neutron log,etc.,are mainly considered in the paper.Some concrete measures of controlling data quality were put forward on the basis of analyzing the abnormal phenomena of log data and the process of underbalance logging in well Qiongxi-3 and a good result was also obtained from the underbalance logging in well Tongnan-1.