Technology and Applications of Foam Drilling Fluid in Fractured and Complex Formations

Fractured and complex formations where types of fractured and porous mud loss occurred in commonly induced instability of wellbore and drilling accidents such as borehole collapse and blowout; therefore, it is the technological bottleneck for the development of oil and gas. Solid free recyclable foam drilling fluid was developed and aimed to deal with the MIS oilfield of Iran, which has abnormally low pressure and developed fracture-cave hydrocarbon reservoir with a high concentration of H2S, which has problems such as serious lost circulation and H2S risk. A sectionalized drilling fluid system has been adopted in this oilfield, and drilling with water can meet the operation requirements during first spud and saturated salt polymer system or undersaturated salt polymer in second spud; the horizontal section adopts solid free recyclable foam drilling fluid to achieve near balance drilling and effectively solves the lost circulation problem in fractured limestone formation. The spot application indicates that solid free recyclable foam drilling fluid has excellent rheology, and meets the requirement of drilling engineering. Meanwhile, the system can retard the H2S corrosion effect on drillstring and guarantee to provide a good MWD transmission signal. A new idea has been provided for drilling engineering in fractured and complex formations.