Geomechanical modeling using the depth-of-damage approach to achieve successful underbalanced drilling in the Gulf of Suez rift basin

Abstract

Typical oil and gas reservoirs producing in the Gulf of Suez are now extensively depleted in terms of recovery of conventional resources and display declining production levels and heterogeneous pore pressure regimes. To continue production on a commercially viable basis and enhance the recovery of remaining oil and gas from the mature reservoirs currently in production, drilling decision-makers can no longer rely on traditional balanced or overbalanced drilling methods. Hence, underbalanced drilling is an essential requirement for such reservoirs. However, inducing underbalanced conditions increases the risk of the borehole instability. In the studied area, three previous wellbore stability studies were performed associated with the Hilal-X platform wells using the breakout-width-failure concept. Nevertheless, several wellbore instability issues were recorded there due to that method determining a mud-weight window that was too conservative. New wellbore stability analysis has been performed using a depth-of-damage approach. This analysis has helped to deliver excellent results during underbalanced drilling, after many attempts in previously drilled wells in overbalanced conditions that resulted in borehole instability and/or formation damage. This study documents how successful underbalanced drilling has been achieved in this basin for the first time by mud weights being guided by depth-of-damage analysis, highlight the requirements of that method using a case study for a specific well. In-situ stresses and an 1D-geomechanical earth model were generated using well log data from offset wells. The modified Lade method was used as a failure criterion, while the depth-of-damage approach was used for wellbore stability analysis in Hilal-X4 well. The study reveals that: 1) the Hilal field reservoirs have variable pore pressure regimes, 2) the breakout-width-failure concept provides misleading results in the studied reservoir formation, 3) the depth-of-damage approach reflects reservoir conditions more effectively and allows for successful underbalanced drilling without any instability events, 4) a new casing design for the Hilal Field wells has led to enhanced production performance, and 5) underbalanced drilling, when downhole pressures are carefully managed, is a safe and reliable technique for the mature fields of the Gulf of Suez rift basin.