CORK : A HYDROLOGIC SEAL AND DOWNHOLE OBSERVATORY FOR DEEP-OCEAN BOREHOLES
CORK : A HYDROLOGIC SEAL AND DOWNHOLE OBSERVATORY FOR DEEP-OCEAN BOREHOLES
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CORK：深海钻孔的水文密封和井下观测站
DOI：
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发表时间：
2006
期刊：
影响因子：
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通讯作者：
R. Macdonald
中科院分区：
文献类型：
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作者：
E. Davis;K. Becker;T. Pettigrew;B. Carson;R. Macdonald
一种新的工具已经开发并成功部署，它提供了一种手段，通过这种手段，海洋钻探计划钻的套管再入孔可以进行水文密封和仪表化。密封件防止水流入或流出孔，否则会对所钻地层造成严重的热和化学干扰。密封件能够承受可能存在于热液或构造活动环境中的正压差和负压差，并且可以在以后的钻井操作中移除。该仪器是为大洋钻探计划第139航次期间的初始部署而开发的，其设计目的是在钻探扰动恢复期间和之后监测地层温度和压力长达2年。记录仪测量密封件下方钻孔中的绝对压力。一个包含10个热敏电阻的传感器串和一个流体采样管悬挂在记录包下面的孔中。取样管穿过密封件延伸到端口，允许测量压差并从孔内深处抽取流体。数据恢复和流体采样可以通过潜水器或遥控潜水器进行。在Juan de Fuca海岭北方沉积物丰富的中谷裂谷部署了两支部队。第一个安装在857 D孔，该孔钻到海底以下936米的总深度，穿过470米的浊流沉积物，进入一个高渗透性的沉积物-岩床复合体，推测该复合体是一个沉积物封闭的热液“储层”。“第二个部署在858 G孔，该孔钻到海底以下433米的总深度，进入一个位于热液喷口区下面的埋藏火山建筑物。部署后约三周，数据从两个孔中成功恢复。858 G孔记录的温度和压力表明，钻井和通过附近未加套管的勘探孔（未充分用水泥密封）向下流入地层的流体严重影响了地层条件。858 G孔中密封件两端的压差最初为-0.24 MPa，在数据恢复时变得越来越负。857 D孔记录的温度和压力似乎正在从钻井干扰中缓慢恢复。最初，该孔中密封件两端的压差为-1.10 MPa;在数据恢复时，压差已降至-0.55 MPa。该仪器将继续监测地层压力和温度，每小时一次，为期2年。
A new tool has been developed and successfully deployed that provides a means by which cased reentry holes drilled by the Ocean Drilling Program can be hydrologically sealed and instrumented. The seal prevents flow of water into or out of a hole that would otherwise cause severe thermal and chemical disturbance to the formation drilled. The seal is capable of withstanding both positive and negative differential pressures that may be present in hydrothermally or tectonically active environments, and can be removed for later drilling operations. The instrumentation, developed for initial deployments during Ocean Drilling Program Leg 139, was designed to monitor the formation temperatures and pressures for up to 2 years during and following the recovery from drilling disturbances. A recording gauge measures absolute pressure in the borehole below the seal. A sensor string containing 10 thermistors and a fluid-sampling tube hang in the hole below the recording package. The sampling tube extends through the seal to a port, allowing the differential pressure to be measured and fluids to be tapped from deep within the hole. Data recovery and fluid sampling can be done via submersible or remotely operated vehicle. Two units were deployed in the sediment-filled Middle Valley rift of the northern Juan de Fuca Ridge. The first was installed in Hole 857D, which was drilled to a total depth of 936 meters below seafloor, through 470 m of turbidite sediment and into a highly permeable sediment-sill complex that is inferred to be a sediment-sealed hydrothermal "reservoir." The second was deployed in Hole 858G, which was drilled to a total depth of 433 meters below seafloor into a buried volcanic edifice that underlies a hydrothermal vent field. Data were recovered successfully from both holes about three weeks after deployment. Temperatures and pressures recorded in Hole 858G show that formation conditions are severely affected by drilling and by downward fluid flow into the formation through a nearby uncased exploratory hole that was not adequately sealed with cement. The differential pressure across the seal in Hole 858G was initially -0.24 MPa, and at the time of the data recovery was becoming increasingly negative. Temperatures and pressures recorded in Hole 857D appear to be recovering slowly from drilling disturbances. Initially, the differential pressure across the seal in this hole was -1.10 MPa; at the time of the data recovery, the differential had reduced to -0.55 MPa. The instruments will continue to monitor formation pressures and temperatures once per hour for 2 years.