标题：SAFETYANALYSIS OF WELLBORE INSTABILITY IN ORDOS BASIN AND RESEARCH ON
ENVIRONMENTAL FRIENDLY STRONG SUPPRESSION ANTI-COLLAPSE DRILLING FLUID TECHINOLOGY
摘要：Borehole instability is one of the most serious complex situations that affect the safety of drilling operations, which has always been the main tech-nical bottleneck restricting safe, efficient, and fast drilling. The inhibition and plugging properties of drilling fluids are the key to effectively solving the problem of borehole instability. Drilling fluids must not only meet the technical requirements of drilling engineering, but also have good environ-mental protection performance. Aiming at the tech-nical problems of wellbore instability in the Fuxian Oilfield in the Ordos Basin, this paper carries out a statistical analysis of the safety of wellbore instabil-ity. The average single well encountered resistance and stuck loss time was 3.64 days,and the average caliper expansion rate of complex layers reached 34.99-42.41%. From the perspective of the mineral composition, microstructure, and physical and chemical properties of the complex formations, it re-veals the instability mechanism of the Liujiagou, Shiqianfeng and Shihezi formations in the Fuxian Oilfield. The clay content in mudstone is relatively high (32.25%), mainly illite/smectite mixed layer (48%).Formation pores and fractures are well devel-oped, providing space for shale hydration. The junc-tion of Shiqianfeng Formation and Shihezi For-mation has strong hydration dispersion and expan-sion. Rock shows strong characteristics of hard and brittleness, and pressure fluctuations can easily lead to the expansion and intersection of micro-fractures around the well and cause the well wall to collapse. Based on the design principle of"inhibition of hy-dration-physical plugging-effective stress support-activity balance"multiple coordinated anti-collapse drilling fluids,and the principle ofexcellent environ-mental performance of drilling fluid treatment agents, an environmentally friendly, strong-inhibition and anti-collapse drilling fluid system suitable for Fuxian Oilfield has been constructed. The drilling fluid sys-tem has good rheology. The filtrationloss under high temperature and high pressure is only 8.8mL. In ad-dition, it has good lubrication perfommance, strong anti-collapse and plugging ability, and excellent en-vironmental performance. The 400um micro-crack pressure bearing capacity reaches 6MPa.Overall, the designed drilling fluid can ensure the "safe,efficient and environmentally friendly" drilling construction in Fuxian Oilfield.
