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Drilling optimization based on a geomechanical analysis using probabilistic risk assessment, a case study from offshore Iran

Rafieepour, S ; Sharif University of Technology

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  1. Type of Document: Article
  2. Abstract:
  3. In offshore Iran, wellbore instability is quite common and the main cause for most of problems during drilling operations. In this study, the existing relevant logs, drilling and other data from offset well were analyzed and integrated to construct a precise Mechanical Earth Model (MEM) describing pore pressure, stress magnitudes and orientation, and formation mechanical properties of the South Pars Gas field. Then, the constructed MEM was refined and calibrated using the existing caliper, image logs, rock mechanical core test and drilling data and through history matching to constrain and reduce the uncertainties associated with limitations and availability of the existing data. Using the validated MEM built for offset well, a sensitivity analysis by formation was performed to evaluate optimum drilling parameters and to evaluate the stability of future deviated or horizontal wells in the field. Finally, a quantitative risk study was conducted to assess the sensitivity of breakout and fracturing mud weights to various input parameters. Results indicate that the stable mud weight window decreases as the borehole deviation increases in the most of formations except reservoir section. It was shown that well azimuth has very little impact on the breakout mud weight, while the breakdown mud weight is significantly higher in wells drilled in the minimum horizontal stress direction. Moreover, It would be better to keep the well deviation as low as possible and not more than 45 and 60 degrees in the Kazhdumi and Fahlyan-Surmeh formations, respectively
  4. Keywords:
  5. Gas industry ; Horizontal wells ; Mechanical properties ; Offshore boreholes ; Offshore drilling ; Offshore gas fields ; Offshore oil wells ; Petroleum reservoir evaluation ; Petroleum reservoirs ; Risk assessment ; Rock drilling ; Rock mechanics ; Rocks ; Stresses ; Borehole deviation ; Drilling operation ; Drilling optimization ; Drilling parameters ; Mechanical earth models ; Mud weight windows ; Probabilistic Risk Assessment ; Wellbore instability ; Horizontal drilling
  6. Source: Rock Engineering and Rock Mechanics: Structures in and on Rock Masses - Proceedings of EUROCK 2014, ISRM European Regional Symposium ; 2014 , pp. 1415-1422 ; ISBN: 9781138001497
  7. URL: http://www.crcnetbase.com/doi/abs/10.1201/b16955-246