Abstract This work presents the assessment of overburden stress, pore pressure and fracture pressure distribution in the Paleozoic stratigraphic units in the Takouazet field, eastern Illizi basin, Algeria. We studied a vertical exploration well, where significant hydrocarbon discoveries have been established in Devonian and Ordovician sandstone reservoirs. Overburden stress interpreted from density log has an average 1.07 PSI/ft (24204.04 Pa/m) gradient. Pore pressure derived from sonic log reveals that hydrostatic conditions prevail in Devonian and Ordovician units, whereas abnormal pore pressure with a maximum 0.66 PSI/ft (14929.60 Pa/m) gradient was recorded against the marine Silurian shale. Fracture pressure was modeled using effective stress ratio models as well as a Poisson's ratio based approach. Rock property based fracture pressure estimate is more sensitive to lithological variations and hence this estimate was used for determining safe drilling mud window and casing placements. The estimated pore pressure and fracture pressure were calibrated with direct downhole formation pressure measurements and leakoff test (LOT)measurements, respectively. Shear failure using Mohr- Coulomb rock failure criterion detected the minimum allowable mud pressure to avoid wellbore instability issues and the result was validated with caliper log observations. It indicated that solid production from the reservoir is very likely during initial production from the reservoir and a solid control mechanism has been suggested. Also widening of breakouts and deteriorating wellbore interpreted from time lapse formation imaging logs strongly suggest against open-hole completion. Based on interpreted pressure gradients and image log analyses, optimum drilling (mud and casing design) and completion policies were recommended for safe and successful operational planning.

中文翻译：

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孔隙压力、破裂压力、剪切破坏的特征及其对钻井、井筒稳定性和完井设计的影响——来自阿尔及利亚伊利齐盆地 Takouazet 油田的案例研究

摘要 这项工作对阿尔及利亚伊利齐盆地东部 Takouazet 油田古生界地层单元的上覆应力、孔隙压力和破裂压力分布进行了评估。我们研究了一口垂直勘探井，在泥盆系和奥陶系砂岩储层中已经发现了重要的油气发现。从密度测井解释的上覆应力具有平均 1.07 PSI/ft (24204.04 Pa/m) 梯度。来自声波测井的孔隙压力显示，泥盆纪和奥陶纪单元存在流体静力条件，而海相志留系页岩记录到的异常孔隙压力最大为 0.66 PSI/ft (14929.60 Pa/m) 梯度。使用有效应力比模型以及基于泊松比的方法对断裂压力进行建模。基于岩石特性的裂缝压力估计对岩性变化更敏感，因此该估计用于确定安全钻井泥浆窗口和套管放置。估计的孔隙压力和破裂压力分别通过直接井下地层压力测量和泄漏测试 (LOT) 测量进行校准。使用 Mohr-Coulomb 岩石破坏准则的剪切破坏检测到最小允许泥浆压力，以避免井眼不稳定问题，结果通过卡尺测井观测进行验证。这表明在储层初始生产期间很可能从储层中产生固体，并提出了固体控制机制。从时间推移地层成像测井中解释的突破和恶化的井眼也强烈表明不利于裸眼完井。基于解释的压力梯度和图像测井分析，推荐了最佳钻井（泥浆和套管设计）和完井政策，以实现安全和成功的运营规划。