DETERMINATION AND CONTROL OF THE DENSITY OF DRILLING FLUIDS DURING UNDERBALANCED DRILLING

As a new technology served to exploration and development of oil fields,underbalanced drilling technologies have been developed rapidly in China and overseas.However,only little studies of design theories and control techniques on bottomhole negative differential pressure were conducted.In this paper,the determining factors of bottomhole negative differential pressure and calculation methods of drilling fluids during underbalanced drilling are described in detail.Simultaneously,several practical approaches controlling bottomhole negative differential pressure and the density of drilling fluids during underbalanced drilling are discussed.The theoretic models and control approaches provided in the paper have been successfully applied in several oil wells with the technology of underbalanced drilling.