Worldwide increase demand for oil and gas led to an evolution in drilling techniques that maximize oil and gas production such as inclined, multilateral, and long horizontal drilling. The interaction of the drilling fluid and mud filtration with the penetrated formation is very critical and very important to be evaluated especially in the case of horizontal drilling where the drilling operation may take more than 20 days. This study aims to assess the effect of exposure time on the changes of the unconfined compressive strength (UCS) while drilling horizontal sandstone formation using water-based drilling fluid. Modified high-pressure high-temperature (HPHT) filter press cell was used to soak Buff Berea sandstone cores with barite-weighted mud under 300 psi differential pressure and 200 °F temperature for different periods. Nuclear magnetic resonance (NMR) was used to assess the change of the porosity while the scratch test was conducted to evaluate the changes in the UCS. The obtained results showed that UCS decreased significantly with increasing exposure time. For instance, the UCS was reduced by 18% after 5 days. NMR results confirmed that there was a corresponding increase in formation damage as shown by a progressive decrease in the rock porosity and permeability with time. The exposure time was found to be a controlling factor for both reducing the rock UCS and porosity. The statistical analysis showed that there is an inverse linear relationship (with 0.92 coefficient of determination R²) between the UCS values vs the extended exposure time. Meanwhile, an approximate logarithmic relationship (with R² of 0.98) for estimating the reduction in rock porosity with the exposure time was investigated.

全球范围内对石油和天然气的需求不断增长，导致了钻井技术的发展，从而使油气产量最大化，例如倾斜，多边和长水平钻井。钻井液和泥浆过滤与渗透地层的相互作用非常关键，而且非常重要，要进行评估尤其是在水平钻井的情况下，钻井作业可能需要20天以上。这项研究旨在评估暴露时间对无侧限抗压强度（UCS）变化的影响），同时使用水性钻井液进行水平砂岩地层的钻探。在300 psi的压差和200°F的温度下，使用改良的高压高温（HPHT）压滤机将重晶石加重的泥浸入Buff Berea砂岩岩心中，持续不同的时间。核磁共振（NMR）用于评估孔隙率的变化，而刮擦测试用于评估UCS的变化。获得的结果表明，UCS随着暴露时间的增加而显着降低。例如，UCS5天后减少了18％。NMR结果证实，地层破坏相应增加，如岩石孔隙度和渗透率随时间逐渐降低所显示。发现暴露时间是降低岩石UCS和孔隙率的控制因素。统计分析表明，UCS值与延长的曝光时间之间存在反线性关系（测定系数R ²为0.92 ）。同时，研究了估计对数关系（R ²为0.98），以估计岩石孔隙度随暴露时间的降低。