Khan Majedul Islam, Das Pranta, Mogira Md Abu, Howladar M Farhad, Chnapa Sushmita Sarker, Chowdhury Mohammad Saeiduj Jaman
Department of Petroleum and Mining Engineering, Shahjalal University of Science and Technology, Sylhet, 3114, Bangladesh.
Heliyon. 2024 Aug 2;10(15):e35622. doi: 10.1016/j.heliyon.2024.e35622. eCollection 2024 Aug 15.
Cementing is an essential downhole operation during the drilling of oil, gas, and geothermal wells, with the primary objective of providing structural support and a seal in the wellbore. It is important to attain adequate cement strength to preserve well integrity, inhibit fluid movement, enhance zonal isolation, and hold the wellbore casing in place. However, a significant challenge arises from the potential contamination of the cement by drilling mud (DM) during the placement process. This study aims to assess the impact of both water-based drilling mud (WBDM) and oil-based drilling mud (OBDM) contamination on the strength of API Class G wellbore cement by comprehensively investigating the underlying causes and the mechanism of strength degradation. Following a systematic methodological approach and the guidelines provided by API and ASTM, cement slurries were prepared and contaminated with DM at 10 %, 20 %, and 30 % concentrations by volume. Subsequently, both neat and contaminated samples were cured for 1, 3, 7, and 14 days, after which a series of uniaxial compressive strength (UCS) tests were conducted, and the results were further reinforced by microstructural and petrophysical property analysis. The results demonstrate that both WBDM and OBDM contamination significantly reduce cement strength, irrespective of curing time. Though the effect of OBDM contamination appears to be more pronounced, the effect of WBDM contamination is also remarkable. After final curing of 14 days, WBDM-contaminated cement samples exhibited an average strength reduction of 45.06 %, while OBDM contamination led to a 66.32 % reduction in strength compared to the neat cement with 30 % contamination. Additionally, for the same curing time and contamination percentage, porosity was found to be increased by 71.18 % and 91.33 %, respectively. The mechanism of neat and contaminated cement hydration is explained with the support of SEM-EDS tests, which confirmed the presence of contamination and revealed how two different drilling muds generate dissimilar pore structures within the cement sheath, affecting the hydration and ultimately contributing to the observed reduction in strength. The findings quantify the negative impact of WBDM and OBDM contamination on wellbore cement, emphasizing the importance of mitigating mud contamination during cementing operations.
固井是石油、天然气和地热井钻井过程中的一项重要井下作业，其主要目的是在井筒中提供结构支撑和密封。获得足够的水泥强度对于保持井的完整性、抑制流体流动、增强层间封隔以及固定井筒套管至关重要。然而，在水泥浆注入过程中，钻井泥浆（DM）可能会污染水泥，这带来了一个重大挑战。本研究旨在通过全面调查强度降低的根本原因和机制，评估水基钻井泥浆（WBDM）和油基钻井泥浆（OBDM）污染对API G级井筒水泥强度的影响。按照系统的方法和美国石油学会（API）及美国材料与试验协会（ASTM）提供的指南，制备了水泥浆，并分别用体积浓度为10%、20%和30%的钻井泥浆进行污染。随后，将纯水泥样品和受污染样品养护1天、3天、7天和14天，之后进行一系列单轴抗压强度（UCS）测试，并通过微观结构和岩石物理性质分析进一步强化测试结果。结果表明，无论养护时间如何，WBDM和OBDM污染都会显著降低水泥强度。虽然OBDM污染的影响似乎更明显，但WBDM污染的影响也很显著。在最终养护14天后，受WBDM污染的水泥样品平均强度降低了45.06%，而受OBDM污染且污染率为30%时，与纯水泥相比强度降低了66.32%。此外，对于相同的养护时间和污染百分比，孔隙率分别增加了71.18%和91.33%。通过扫描电子显微镜 - 能谱（SEM - EDS）测试对纯水泥和受污染水泥的水化机制进行了解释，该测试证实了污染的存在，并揭示了两种不同的钻井泥浆如何在水泥环套内产生不同的孔隙结构，影响水化过程并最终导致观察到的强度降低。研究结果量化了WBDM和OBDM污染对井筒水泥的负面影响，强调了在固井作业中减轻泥浆污染的重要性。
