鄂尔多斯盆地东部刘家沟组反复井漏机理及治理措施OA

In order to address the challenges of repeated lost circulation in network fracture developed-stratum at the bottom of Liujiagou formation in eastern Ordos Basin,the mineralogical natures of rocks were analyzed by using X-ray diffraction and scanning electronic microscope,and flow tests on water sensitivity and velocity sensitivity of rocks were conducted,which revealed that the clay minerals in target stratum reaches as high as 22%to 67%,exhibiting stronger water sensitivity and velocity sensitivity,leading to weakness of the fracture wall strength and increase of the fracture width.The conventional lost circulation materials are prone to corrosion and fail to prop up the fractures,resulting in diminished plugging effect and ultimately repeated lost circulation.Thus,a weak gel-bridge plug composite lost circulation material with high suspension capacity and alkali corrosion resistance was introduced.This kind of material enables to largely invade the lost circulation channels to block the contact between drilling fluid and fracture walls,thereby inhibiting water sensitivity and velocity sensitivity.Laboratory slot tests show that the fluid loss gradually stabilizes with further pressure increases after the pressure climbs to 6 MPa,and the pressure essentially remains unchanged after 50 minutes of shut-in.Field trials in 40 wells reached a primary success ratio of 97.5%without recurrence of lost circulation.This research offers an effective solution for repeated lost circulation in fractured strata with strong water sensitivity and velocity sensitivity,and also points to a direction for the development of novel plugging materials.