The infiltration of drilling fluids into stratified shale and the subsequent degradation of its strength play a critical role in borehole instability, with the mechanisms in stratified shale differing significantly from those in conventional mudstone. This study aims to elucidate the strength degradation mechanisms of stratified shale under the influence of water-based and oil-based drilling fluids. Laboratory experiments were conducted to collect relevant parameters, and the driving forces of different drilling fluids during their penetration into stratified shale joints were compared and analyzed. Through drilling fluid intrusion experiments, the patterns of drilling fluid penetration into stratigraphic joints were examined. Furthermore, the degradation of shale strength following fluid intrusion was evaluated by measuring mechanical parameters after the intrusion process. Based on these measurements, the study analyzed the causes of shale strength deterioration due to the intrusion of various types of drilling fluids. the intrusion of drilling fluids along the stratified joints causes its strength deterioration, and the intrusion driving force of drilling fluids is mainly controlled by the capillary force when the size of the stratified joints is less than 0.007 μm, and vice versa by the bottomhole differential pressure; the driving force for fluid intrusion into smaller stratified joints is greater, but due to differences in permeability, drilling fluids are more likely to infiltrate larger stratified joints, and its strength degradation of shale is mainly due to the lubrication of filtration fluid on the formation surface and the hydrodynamic spiking effect, which is dominated by the physical effect; the depth of intrusion of water-based drilling fluid is slightly smaller than that of oil-based drilling fluid, but the hydration of illite surface caused by the filtration fluid will result in the serious dispersal of shale, and its strength degradation is controlled by the combination of physical and chemical effects.
[1] Bo W, Sun J S, Feng S. Mechanism of wellbore instability in continental shale gas horizontal sections and its water-based drilling fluid countermeasures[J]. Natural Gas Industry B, 2020, 6(7): 680-688.
[2] Li Z, Li G, Li H. Shale damage simulation considering shale swelling during shale-liquid interaction[J]. Fuel, 2023, 339: 127423.
[3] 刘均一, 郭保雨. 页岩气水平井强化井壁水基钻井液研究[J]. 西安石油大学学报(自然科学版), 2019, 34(2): 86-92, 98.
[4] 韩磊. 基于流固耦合理论的页岩井壁稳定性研究[D]. 青岛: 中国石油大学(华东), 2021.
[5] Cheng W, Jiang G, Li X. A porochemothermoelastic coupling model for continental shale wellbore stability and a case analysis[J]. Journal of Petroleum Science and Engineering, 2019, 182: 106265.
[6] 穆英, 胡志明, 端祥刚, 等. 页岩吸水对储层的作用机理研究[J]. 天然气与石油, 2020, 38(6): 73-79.
[7] Yan C, Dong L, Zhao K. Time-dependent borehole stability in hard-brittle shale[J]. Petroleum Science, 2022, 19(2): 663-677.
[8] 卢运虎, 梁川, 金衍, 等. 高温下页岩水化损伤的各向异性实验研究[J]. 中国科学: 物理学力学天文学, 2017, 47: 114614.
[9] 赵志红, 金浩增, 郭建春, 等. 水化作用下深层页岩软化本构模型研究[J]. 岩石力学与工程学报, 2022, 41(增2): 3189-3197.
[10] 刘敬平, 孙金声. 页岩气藏地层井壁水化失稳机理与抑制方法[J]. 钻井液与完井液, 2016, 33(3): 25-29.
[11] 王波, 孙金声, 申峰, 等. 陆相页岩气水平井段井壁失稳机理及水基钻井液对策[J]. 天然气工业, 2020, 40(4): 104-111.
[12] Liu J, Yang Z, Sun J. Experimental investigation on hydration mechanism of Sichuan shale (China)[J]. Journal of Petroleum Science and Engineering, 2021, 201: 108421.
[13] 金衍, 薄克浩, 张亚洲, 等. 深层硬脆性泥页岩井壁稳定力学化学耦合研究进展与思考[J]. 石油钻探技术, 2023, 51(4): 159-169.
[14] 鲁超凡. 乾安地区青山口组地层防塌钻井液技术研究[D]. 大庆:东北石油大学,2023.
[15] 熊健, 李羽康, 刘向君, 等. 水岩作用对页岩岩石物理性质的影响——以四川盆地下志留统龙马溪组页岩为例[J]. 天然气工业, 2022, 42(8): 190-201.
[16] 邓富元, 何世明, 赵转玲, 等. 逆流自吸效应对页岩油储层坍塌压力的影响研究[J]. 石油钻探技术, 2019, 47(1): 37-44.
[17] 王跃鹏, 刘向君, 梁利喜, 等. 黏土矿物水化膨胀及无机盐溶液对其抑制作用[J]. 科学技术与工程, 2022, 22(22): 9574-9581.
[18] 王跃鹏, 刘向君, 熊健, 等. 富有机质页岩水化特征的试验研究[J]. 地下空间与工程学报, 2022, 18(3): 891-900.
[19] He S, Liang L, Zeng Y. The influence of water-based drilling fluid on mechanical property of shale and the wellbore stability[J]. Petroleum, 2016, 2(1), 61-66.
[20] 戴文浩. 页岩气地层水基钻井液体系优化实验研究[D]. 青岛: 中国石油大学(华东), 2017.
[21] Gholami R, Elochukwu H, Fakhari N. A review on borehole instability in active shale formations: Interactions, mechanisms and inhibitors[J]. Earth-Science Reviews, 2018, 177: 2-13.
[22] 徐建根. 页岩气地层水基钻井液稳定井壁技术研究[D]. 青岛: 中国石油大学(华东), 2019.
[23] 丁乙, 刘向君, 曹雯, 等. 页岩渗吸过程中的水化损伤演化特征研究[J]. 工程地质学报, 2024, 32(4):1262-1272.
[24] 曾凡辉, 张蔷, 陈斯瑜, 等. 水化作用下页岩微观孔隙结构的动态表征——以四川盆地长宁地区龙马溪组页岩为例[J]. 天然气工业, 2020, 40(10): 66-75.
[25] 晏军, 张潇, 梁冲, 等. 钻井液处理剂对长宁地区页岩抗压强度的影响研究[J]. 钻采工艺, 2019, 42(3): 13-16, 6.
[26] 梁利喜, 王光兵, 刘向君, 等. 页岩水化特征及其井壁稳定分析[J]. 中国安全生产科学技术, 2017, 13(9): 77-83.
[27] He S, Liang L, Zeng Y. The influence of water-based drilling fluid on mechanical property of shale and the wellbore stability[J]. Petroleum, 2016, 2(1): 61-66.
[28] 孙金声, 蒋官澄, 贺垠博, 等. 油基钻井液面临的技术难题与挑战[J]. 中国石油大学学报(自然科学版), 2023, 47(5): 76-89.
[29] You L, Kang Y, Chen Z. Wellbore instability in shale gas wells drilled by oil-based fluids[J]. International Journal of Rock Mechanics and Mining Sciences, 2014, 72: 294-299.
[30] Li X, Yan X, Kang Y. Investigation of drill-in fluids damage and its impact on wellbore stability in Longmaxi shale reservoir[J]. Journal of Petroleum Science and Engineering, 2017, 159: 702-709.
[31] 杨智光, 李吉军, 齐悦, 等. 松辽盆地富含伊利石的古龙页岩水化特性及其对岩石力学参数的影响[J]. 大庆石油地质与开发, 2022, 41(3): 139-146.
[32] 刘厚彬, 孙航瑞, 崔帅, 等. 层理性页岩变形机理及力学特性研究[J]. 地下空间与工程学报, 2023, 19(增1): 174-180.
[33] 王小军, 崔宝文, 冯子辉, 等. 古龙页岩微—纳米孔缝油气原位形成与富集机制[J]. 石油勘探与开发, 2023, 50(6): 1-11.
[34] 孙龙德, 王小军, 冯子辉, 等. 松辽盆地古龙页岩纳米孔缝形成机制与页岩油富集特征[J]. 石油与天然气地质, 2023, 44(6): 1350-1365.
[35] Sanfillippo F, Brignoli M, Santarelli FJ. Characterization of conductive fractures while drilling[A]// SPE European Formation Damage Conference[C]. 1997: 2-3.
[36] Liu Y X, Guo J C, Chen Z X. Leakoff characteristics and an equivalent leakoff coefficient in fractured tight gas reservoirs[J]. Journal of Natural Gas Science and Engineering, 2016, 31(4): 603-611.
