Gamal Hany, Elkatatny Salaheldin
Department of Petroleum Engineering, College of Petroleum Engineering & Geosciences, King Fahd University of Petroleum & Minerals, Dhahran 31261, Saudi Arabia.
ACS Omega. 2022 Sep 29;7(40):35961-35969. doi: 10.1021/acsomega.2c05032. eCollection 2022 Oct 11.
The rock saturation condition affects the rock elastic and strength characteristics due to the role of fluid-rock interaction. However, the role of this parameter has not been studied well for mud-rock exposure during drilling operations. Hence, this study targets to assess the role of different rock saturation conditions on the rock geomechanics changes during the rock exposure for the drilling fluids. During the drilling operation, the mud filtrate invades the drilled formation pore system and replaces the saturating fluid and consequent alterations occur for the rock elastic moduli and failure properties. The current study employed Berea Buff sandstone rock type with different saturation conditions (brine-saturated, dry, and oil-saturated) to interact with drilling mud (water-based) through the filtration test to mimic the downhole rock-mud exposure under pressure, temperature, and time conditions. Extensive laboratory analysis was accomplished that covered the scratching test to get the strength of rock samples, acoustic data determination, elastic moduli evaluation, and scanning electron microscopy to assess the internal alterations of the rock pore system. The obtained results showed that the oil-saturated sample showed the least filtration characteristics for the rock-mud exposure and the best condition to maintain the rock strength from deterioration compared to the dry and brine-saturated samples. The rock strength showed a weakening behavior for the brine-saturated and dry samples by 5 and 18% respectively, while the oil-saturated sample showed only a 2% strength reduction after the mud exposure. Poisson's ratio showed a 21% increase for the brine-saturated sample and the dry sample showed a small increase from 0.2 to 0.22, while the oil-saturated sample maintains a stable Poisson's ratio at 0.24. Young's modulus showed an increase for the dry and brine-saturated rock samples by 10 and 7%, respectively, while a 25% reduction for the oil-saturated. The spectrometry analysis results showed the internal changes in the rock samples' pore system for the brine-saturated and dry samples, while the oil-saturated sample showed no internal changes that maintain the rock structure and strength after the mud exposure.
由于流体 - 岩石相互作用，岩石饱和状态会影响岩石的弹性和强度特性。然而，在钻井作业中，对于泥岩暴露时该参数的作用尚未得到充分研究。因此，本研究旨在评估不同岩石饱和条件对钻井液岩石暴露过程中岩石地质力学变化的作用。在钻井作业过程中，泥浆滤液侵入钻孔地层孔隙系统并取代饱和流体，从而导致岩石弹性模量和破坏特性发生变化。本研究采用具有不同饱和条件（盐水饱和、干燥和油饱和）的贝雷阿缓冲砂岩，通过过滤试验使其与钻井泥浆（水基）相互作用，以模拟井下岩石在压力、温度和时间条件下与泥浆的接触情况。完成了广泛的实验室分析，包括划痕试验以获取岩石样品的强度、声学数据测定、弹性模量评估以及扫描电子显微镜检查以评估岩石孔隙系统的内部变化。所得结果表明，与干燥和盐水饱和样品相比，油饱和样品在岩石与泥浆接触时表现出最小的过滤特性，并且是保持岩石强度不恶化的最佳条件。盐水饱和和干燥样品的岩石强度分别降低了5%和18%，而油饱和样品在泥浆接触后仅表现出2%的强度降低。泊松比方面，盐水饱和样品增加了21%，干燥样品从0.2小幅增加到0.22，而油饱和样品在0.24保持稳定的泊松比。杨氏模量方面，干燥和盐水饱和岩石样品分别增加了10%和7%，而油饱和样品降低了25%。光谱分析结果显示了盐水饱和和干燥样品岩石样品孔隙系统的内部变化，而油饱和样品在泥浆接触后未显示内部变化，保持了岩石结构和强度。
