Abstract

This work interprets the pore pressure distribution and in-situ stress magnitudes in the ~ 10,600 feet thick Neogene succession of the West and South Al-Khilala gas fields, onshore Nile Delta. The Messinian incised valley-fill (IVF) fluvio-marine sediments host the principal gas-bearing zones having a 0.47 PSI/feet pore pressure gradient, as seen from the downhole measurements. Early Pliocene is marked by a dramatic regional sea-level rise which deposited thick marine shales unconformably above the Abu Madi IVF reservoir facies. A high sedimentation rate during Pliocene retained excess porosity and translated to a mild overpressure of around 0.55 PSI/feet in the Kafr El Sheikh Formation due to compaction disequilibrium. Vertical (S_v), minimum (S_h), and maximum (S_H) horizontal stress gradients are estimated as 0.97–0.98; 0.64–0.76, and 0.86–1 PSI/feet, respectively. Interpreted stress magnitudes decipher a normal to strike-slip stress state in the studied fields. B-Quality wellbore breakouts with ~ 600 feet cumulative length infer NNE-SSW S_H orientation, almost parallel to the motion direction of the African plate. Wellbore stability analysis indicated a minimum mud weight of 11.45 PPG needs to be maintained against the Pliocene shales which exhibited major wellbore instability issues in the exploratory drilling campaign. Based on the interpreted pore pressure, S_h, and collapse pressure gradients, a safe drilling mud window is proposed to ensure borehole stability.

Article highlights

• Pliocene marine shales have mild overpressure resulting from disequilibrium compaction, while the Miocene Abu Madi reservoirs have 0.47 PSI/feet pore pressure gradient.

• Normal to strike-slip stress state in inferred in the West and South Al-Khilala gas fields.

• B-Quality wellbore breakouts infer NNE-SSW S_H orientation.

• Collapse pressure and safe mud weight window are inferred to ensure borehole stability in the Miocene shales.

中文翻译：

---

埃及尼罗河三角洲西部和南部Al-Khilala油气田的孔隙压力，地应力状态和井眼稳定性研究

摘要

这项工作解释了尼罗河三角洲陆上西部和南部Al-Khilala气田约10,600英尺厚的新近纪演替中的孔隙压力分布和原地应力大小。从井下测量中可以看到，墨西拿切开的河谷填充物（IVF）潮红沉积物是主要的含气区，其孔隙压力梯度为0.47 PSI /英尺。上新世早期以区域海平面急剧上升为标志，在阿布马迪IVF储层相上不均匀地沉积了厚厚的海相页岩。上新世期间的高沉积速率保留了过量的孔隙度，并由于压实不平衡而转化为Kafr El Sheikh地层中约0.55 PSI /英尺的轻度超压。垂直（S _v），最小（S _h）和最大（S _H）水平应力梯度估计为0.97–0.98；0.64-0.76和0.86-1-1 PSI /英尺。解释的应力大小在研究的领域中解释了法线到走滑应力状态。B品质井眼的累积长度约为600英尺，可推断为NNE-SSW S _H方向，几乎平行于非洲板块的运动方向。井眼稳定性分析表明，与上新世页岩相比，需要保持最低泥浆重量为11.45 PPG，而该页岩在勘探钻探活动中表现出主要的井眼不稳定问题。基于解释的孔隙压力S _h和塌陷压力梯度，提出了一个安全的钻井泥浆窗口，以确保井眼的稳定性。

文章重点

• 上新世海相页岩因不平衡压实而有轻微的超压，而中新世阿布马迪油藏的孔隙压力梯度为0.47 PSI /英尺。

• 可以推断，西部和南部的Al-Khilala气田具有正常的走滑应力状态。

• B品质井眼突破可推断NNE-SSW S _H方向。

• 推断塌陷压力和安全泥浆重量窗口可确保中新世页岩的井眼稳定性。