--> 1D To 4D Geomechanics Assessment In North Madura Field Lead To Successful Drilling

AAPG Asia Pacific Region GTW, Pore Pressure & Geomechanics: From Exploration to Abandonment

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1D To 4D Geomechanics Assessment In North Madura Field Lead To Successful Drilling

Abstract

Bukit Tua Field which located at offshore East Java Indonesia, is known for its very challenging nature from geological, reservoir and drilling perspectives. The success production story from Petronas previous drilling campaign in year 2015 to 2016 has strengthen the decision to further develop this field with main target complex carbonate reservoir. Previously wellbore instability problems which consist of severe losses, breakouts and weak shale bedding plane failure, then were leading to pack-off and stuck pipes had been successfully minimized by applying well-scale (1D) geomechanics analysis using mechanical earth model. Mechanical Earth Model (MEM) is an essential tool for describing the mechanical responses of the earth to the changes applied to it such as drilling activity, fluid flow, temperature, pressure and stress changes. MEM itself is comprised of elastic properties, rock’s strength properties, pore pressure, overburden stress, minimum and maximum horizontal stresses magnitude with their directions. The application of well-scale MEM had further increased drilling performances in the next well subsequently compared to the first problematic well.

As the production activities continue, it is leading to the further depletions of reservoir pressure. This pressure depletion may induce stress redistribution in the depleted reservoir and surrounding rock. Stress redistribution throughout the field production lifecycle need to be characterized in order to prevent or mitigate possible hazards in the future such as decreasing fracture gradient, bedding plane failure worsening, reservoir compaction, and surface subsidence. Bedding plane failure is one of the main concern related to wellbore instability in the overburden part of the well, especially in Upper carbonate formation. The shale-carbonate interbedding layers in upper carbonate formation combined with high well inclination profile when penetrated these formations are the main cause of bedding plane failures. Bedding plane failure has been minimized during previous drilling campaign by applying plane of weakness analysis. However, this type of instability is getting worse as the depletion in reservoirs triggered the stress changes through the field and affected the stress around bedding plane particularly.

3D geomechanics model is generated using available well-scale MEM data in the field and distributed throughout the field which then guided by seismic interpretation data as distribution control. The 3D model subsequently being coupled in term of time-lapse (4D) simulation with dynamic pressure data in the main complex carbonate reservoir. Time-lapse (4D) geomechanics simulation is run to captured the possible hazard that might arise due to stress changes related to production activity. The results of this study are seen that there will be negligible reservoir compaction and surface subsidence during drilling in present-day at year 2017 with regards of only one reservoir included in simulation. Bedding plane failure analysis using present-day stress profile from simulation show higher mud weight requirement in effect to reservoir depletions. Two planned wells then drilled guided by the study results and safely drilled with no significant wellbore instability issues and minimum reservoir damage due to optimal mud weight program. 4D Geomechanics assessment managed to answer the drilling challenges and assisted Petronas throughout the drilling campaign to successfully reach its target in safely and timely manner.