Temperature and video logs from the upper oceanic crust, Holes 504B and 896A, Costa Rica Rift flank: implications for the permeability of upper oceanic crust
Temperature and video logs from the upper oceanic crust, Holes 504B and 896A, Costa Rica Rift flank: implications for the permeability of upper oceanic crust
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DOI：
10.1016/j.epsl.2004.03.033
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发表时间：
2004-06-15
影响因子：
5.3
通讯作者：
deMoustier, CP
中科院分区：
文献类型：
--
作者：
Becker, K;Davis, EE;deMoustier, CP
2001年，我们重新考察了哥斯达黎加裂谷南侧厚沉积的5.9 Ma地壳，以便在1993年最后一次钻探8年多后，重新进入两个重要的大洋地壳钻孔--504B和896A孔。在这里，我们报道了通过沉积段在套管内的两个孔中测量的井温，然后进入最上层地下室的裸眼，以及896A井地下室上部的视频记录。自1979年首次进入大洋基底以来，504b孔一直以海底水向最上层基底的井下流动而闻名，这种流动最初很强(约为100 m/h)，但后来减弱；我们的温度数据显示，以0.4 m/h的速度缓慢地向下流动。根据我们的长期水文观测站的绳索安装时获得的压力数据，确定驱动这种缓慢流动的压差为11-12 kpa。流量和压差的组合限制了504b井上基岩段平均渗透率的估计为1-5×10(-14)m(2)，这个值与过去的测定相似，但略低于过去的测定。在896A井中，温度测井显示，地层流体在平均温度为57.8摄氏度、总速度为12米/小时的情况下通过套管流动；它还表明，在最上层的基底中，至少有三个区域产生了不同温度的流体，这些流体对整个流动做出了贡献。虽然896A孔不能测量到相关的压差，但可以通过假设与在也能产生地层流体的基底高地的其他脊侧位置测得的-20kPa值的差值来估计产层剖面的平均渗透率；896A孔最上层基底的渗透率估计值约为1-4×10(-13)m(2)，这也与过去的封隔器测定结果一致。896A井的视频测井提供了前所未有的视觉图像，记录了产层渗透率的离散性质。它还表明，井眼内有大量的细菌絮体，它们可能被生产流体从地层中冲洗出来，或者因生产流体流入的营养物质而在井眼内开花。(C)2004爱思唯尔B.V.保留所有权利。
In 2001, we revisited thickly sedimented 5.9 Ma crust on the southern flank of the Costa Rica Rift for wireline re-entry of two important ocean crustal boreholes, Holes 504B and 896A, more than 8 years after they were last drilled in 1993. Here we report borehole temperatures measured in both holes within casing through the sediment sections and then into open hole in uppermost basement, as well as a video log from the upper basement section of Hole 896A. Since it first penetrated into oceanic basement in 1979, Hole 504B has been known for downhole flow of ocean bottom water into uppermost basement that was initially strong ( approximate to 100 m/h) but then waned; our temperature data indicate a very slow lingering downflow at 0.4 m/h. The pressure differential driving this slow flow was determined to be 11 - 12 kPa from pressure data acquired when the hole was sealed by our wireline installation of a long-term hydrological observatory. The combination of the flow rate and the pressure differential constrains an estimate for the average permeability of the upper basement section in Hole 504B of 1-5 x 10(-14) m(2), a value similar to but slightly less than past determinations. In Hole 896A, which is located similar to 1 km away on a sediment-covered basement high, the temperature log indicated uphole flow of formation fluids at an average temperature of 57.8degreesC and at a total rate of 12 m/ h through casing; it also showed that at least three zones in uppermost basement produce fluids of different temperatures that contribute to this total flow. Although the associated pressure differential could not be measured in Hole 896A, estimates of average permeability of the section with the producing zones can be derived by assuming a differential of - 20 kPa similar to those measured in other ridge-flank sites in basement highs also known to produce formation fluids; estimated permeability values for uppermost basement in Hole 896A are on the order of 1-4 x 10(-13) m(2), again consistent with past packer determinations. The video log in Hole 896A provides unprecedented visual images that document the discrete nature of the permeability of the producing zones. It also suggests an abundance of bacterial floc within the hole that may be either flushed from the formation by the producing fluids or blooming within the hole in response to nutrients advected by the producing fluids. (C) 2004 Elsevier B.V. All rights reserved.