Numerical simulation of the stability a deviated well using FLAC۳D; case study of Lishtar Oil Field, southern Iran

Access to oil and gas reservoirs confronts many problems in different parts of the exploration, drilling, exploitation and processing. In this paper, based on the data of one of the drilled wells in Lishtar oilfield in southern Iran, both analytical (elastic model) and numerical (elasto-plastic model) solutions were used to perform wellbore stability analysis for the whole depth of the studied oil well. First, the mechanical earth model (MEM) was established using petrophysical logs and then validated via direct measurement data such as the leak-off test (LOT) and repeat formation test (RFT). Then, four rock failure criteria namely, Mohr-Coulomb, Mogi-Coulomb, Hoek-Brown, and Modified Lade were employed to predict safe mud weight window for the studied well. Besides, calliper/bit size and image logs were used to verify the predicted mud weight windows. Later, sensitivity analysis of the well trajectories was performed to evaluate the effect of azimuth and inclination angles, and also to specify the most stable orientation for the drilled well. Finally, based on the elasto-plastic model, the numerical simulations using FLAC۳D code was conducted to evaluate the results of analytical solutions and to determine the optimum mud weight based on the Normalized Yielded Zone Area (NYZA). It was found that the Mogi-Coulomb and Hoek-Brown failure criteria with optimized constants resulted in the best prediction of the breakout pressure for the case study. Accordingly, the numerical simulations demonstrated good accordance with the results of analytical solutions based on actual mud weights. According to this study, an elasto-plastic model would be suitable and sufficient to determine the optimum mud weight and to analyse wellbore stability of the studied well.

کلیدواژه ها:

Numerical simulation ، wellbore stability ، FLAC۳D ، Lishtar oilfield