标题：NUMERICAL SIMULATION AND ANALYSIS OF THE BITUMEN INTRUSION MECHANISM BASED ON DENSITY DIFFERENCE BETWEEN BITUMEN AND DRILLING FLUID IN HALFAYA OILFIELD, IRAQ
摘要：High viscosity active bitumen is often drilled during the carbonate reservoirs development in the Middle East, such as Yadavaran oilfield, Halfaya oilfield, Ahdeb oilfield, etc. The distribution rules of bitumen in the stratum is not clear and cannot be effectively predicted. Inter-well formation pressure and great difference in physicochemical properties of bitumen bring great difficulties to the drilling operation. Therefore, an in-depth analysis of bitumen intrusion mechanism is essential to develop effective technical measures to prevent bitumen intrusion and reduce or avoid bitumen pollution. A lot of field experiences show that the density of formation bitumen is usually 0.85〜1.10 g/cm~3, which is lower than that of common drilling fluids. Therefore, it is possible that the density difference between bitumen and drilling fluid leads to the bitumen intrusion into wellbore by gravity displacement under porous media in carbonate reservoirs. The software ECLIPSE was used to simulate and analyze dynamic intrusion process under different density difference conditions. The results show that drilling fluid is easily to leak from the fracture bottom into the formation. Then bitumen is replaced and invaded into the wellbore because of the density difference, which results in the complex situation of well leakage and blowout simultaneously. With the increasing volume of drilling fluid in the fracture, the pressure in the fracture is increased and when it is balanced with the pressure in the drilling fluid column in the wellbore, the bitumen will no longer intrusion into the formation.
