Prediction of Porosity in Compacted Sands
Prediction of Porosity in Compacted Sands
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DOI：
10.1306/m69613c2
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发表时间：
1997
期刊：
影响因子：
--
通讯作者：
J. Gluyas;C. Cade
中科院分区：
文献类型：
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作者：
J. Gluyas;C. Cade
摘要：我们提出了静水压埋藏条件下清洁、刚性颗粒（石英、长石）砂的新孔隙度与深度关系。这样可以在 95% 的置信水平下以 ±2.5 孔隙度单位的精度预测未胶结砂岩的孔隙度。这种关系是利用实验室压实实验的实验数据和世界各地埋藏的未胶结砂岩的现场数据得出的。方程式为： 其中孔隙率 () 的单位为百分比，深度 (z) 的单位为米。通过根据有效应力而不是深度来缩放这种关系，它可以用于对超压环境中未胶结砂的孔隙率提供同样准确的预测。这是使用以下等式完成的： 其中 z = 有效埋深（以米为单位）； z = 埋藏深度（以米为单位）； r = 岩石密度（单位为 Kgm-3 [千克每立方米]）= 通常为 2650； w = 水的密度 (Kgm-3) = 通常为 1050； g = 重力（以 ms-2 [米每平方秒] 为单位）= 9.8； = 上覆岩层的平均孔隙度 = 通常为 0.2； u = 过压（单位为 MPa [兆帕]）。我们认为“仅压实”孔隙度-深度关系具有相当大的价值。仅压实趋势可以准确预测未胶结砂岩的孔隙度，并给出最大孔隙度基线，可与水泥体积和所得胶结砂岩孔隙度进行比较。如果同时包含胶结砂岩和非胶结砂岩数据以产生“孔隙度损失-深度”关系，则该关系中所产生的分散度（对于给定深度通常为±5个孔隙度单位）限制了其有用性。 1 目前隶属关系：Monument Oil and Gas，英国伦敦 End_Page 19------------------------- 在钻井之前，新关系可用于预测已知未胶结砂岩的孔隙度，或对已知或怀疑已胶结砂岩的估计孔隙度设置上限。
ABSTRACT We present a new porosity-depth relationship for clean, rigid grain (quartz, feldspar) sands under hydrostatic burial. This allows the prediction of porosity in uncemented sandstones to an accuracy of ±2.5 porosity units at 95% confidence levels. The relationship was derived using experimental data from laboratory compaction experiments and field data for buried uncemented sandstones from around the world. The equation is: where porosity () is in percentages and depth (z) is in meters. By scaling this relationship in terms of effective stress rather than depth, it can be used to provide an equally accurate prediction of porosity for uncemented sands in overpressured settings. This is done using the following equation: where z = effective burial depth (in meters); z = burial depth (in meters); r = density of rock (in Kgm-3 [kilograms per cubic meter]) = typically 2650; w = density of water (Kgm-3) = typically 1050; g = gravity (in ms-2 [meters per second squared]) = 9.8; = average porosity of overburden = typically 0.2; and u = overpressure (in MPa [megapascals]). We propose that there is considerable value in a "compaction only" porosity-depth relationship. A compaction-only trend allows the accurate prediction of porosity in uncemented sandstones, and gives a maximum porosity baseline to which cement volumes, and resultant cemented sandstone porosities, can be compared. If both cemented and uncemented sandstone data are included to produce a "porosity loss-depth" relationship, the resultant scatter (typically ±5 porosity units for a given depth) in the relationship limits its usefulness. 1 Present affiliation: Monument Oil and Gas, London, United Kingdom End_Page 19------------------------- Prior to drilling, the new relationships may be used either to predict the porosity of sands that are known to be uncemented or to place an upper limit on the porosity estimated for sandstones either known or suspected to be cemented.