NUMERICAL STIMULATION ANALYSIS ON THE CREEP BITUMEN INTRUSION MECHANISM: A CASE OF MISHRIF FORMATION IN HALFAYA OILFIELD, IRAQ

Bitumen has been drilled in the development of Hafaya oilfield in Iraq, Yada Oilfield in Iran and tar sand project in the Gulf of Mexico in recent years. The formation bitumen usually exhibits plastic creep and paste-flow characteristics, and the problems of wellbore instability is prominent. In addition, formation bitumen intrusion into wellbore always seriously deteriorate the performance of drilling fluid, increase the difficulty of ground processing, and cause environmental contamination. However, the mechanism of bitumen intrusion is not clear, and drilling operators cannot take effective measures to prevent bitumen intrusion. Based on the plastic creep characteristics and related parameters of bitumen in Mishrif Formation in Halfaya oilfield, the intrusion mechanism of bitumen was analyzed by ABAQUS Unified Finite Element Analysis (FEA) Software. The results show that the in-situ stress and porosity around the wellbore are obviously changed after bituminous formation was drilled. And the overburden pressure is the main original power of creep bitumen intrusion. The detailed analysis of the creep bitumen intrusion mechanism can provide reliable technical support for the follow-up safe and efficient drilling measures determination during drilling in bituminous formation.