Geomechanical Evaluations Helped Successful Drilling Operation and Completion in Mature Fields with Depleted Reservoirs Interbedded with Weaker Formations
- Abbas Khaksar (Baker RDS Pty Ltd) | Khalil Rahman (Baker RDS) | Adrian White (Geo Mechanics) | Juanih Ghani (Talisman Malaysia Limited) | Mohammad S. Asadi (Baker Hughes) | Keith Stewart (Talisman (Asia) Ltd.)
- Document ID
- International Petroleum Technology Conference
- International Petroleum Technology Conference, 15-17 November, Bangkok, Thailand
- Publication Date
- Document Type
- Conference Paper
- 2011. International Petroleum Technology Conference
- 2 Well Completion, 1.11 Drilling Fluids and Materials, 1.1 Well Planning, 1.6.10 Running and Setting Casing, 4.3.4 Scale, 1.2.2 Geomechanics, 5.3.4 Integration of geomechanics in models, 1.7.2 Managed Pressure Drilling, 1.6 Drilling Operations, 1.11.2 Drilling Fluid Selection and Formulation (Chemistry, Properties), 1.7 Pressure Management, 5.6.1 Open hole/cased hole log analysis, 2.2.2 Perforating, 2.4.3 Sand/Solids Control, 1.6.9 Coring, Fishing, 5.1.10 Reservoir Geomechanics, 1.7.5 Well Control, 5.6.9 Production Forecasting, 3.2.3 Hydraulic Fracturing Design, Implementation and Optimisation, 1.14 Casing and Cementing, 3.2.5 Produced Sand / Solids Management and Control, 1.12.6 Drilling Data Management and Standards
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Hydrocarbon bearing reservoirs in the Southern Fields, Malay Basin, Malaysia contain in excess of 40 sandstone reservoirs interbedded with mudstones and coal seams. Years of production from shallower and mechanically weaker reservoirs resulted in pressure depletion whilst deeper and generally stronger reservoirs are still at early development stages and have normal pressures. High angle and horizontal development wells, to be completed without sand control, are planned for the deep reservoirs.
Reservoir pressure depletion results in a lower fracture gradient and a decrease in the drilling mud weight window. An improperly weighted mud may induce wellbore instability in weaker but normally pressured formations or mud losses while drilling heavily depleted shallow formations. Systematic geomechanical evaluations are required to assess the drillability of shallow depleted reservoirs and the feasibility of horizontal wells without sand control for deeper normally pressured reservoirs.
In a series of studies, a full-scale geomechanical model was developed, validated and updated using core, logs and drilling data from wells in the area. In particular, a total mud loss event in depleted formations in a recent well and rock mechanical data were used to establish the pore pressure-stress coupling (path) factor, an important parameter required for well control and managed pressure drilling operations. Subsequent drilling campaigns have all been successful via good drilling practices and using the recommended mud programs based on previous drilling experience and consistent with wellbore stability assessments. Some cementing issues were reported due to a much lower fracture gradient in the upper depleted sandstones sections but these issues have not prevented safe completion of the wells.
Sand production prediction studies were also carried out for a number of planned wells. Based on sanding assessments, well completion recommendations included cased and perforated completion, barefoot completion and openhole with predrilled liner completion depending on the well trajectory, rock fabrics, rock strengths and production conditions for individual cases. Production experiences to date have been consistent with the model prediction and completion recommendations (i.e. sandfree production from several wells with predrilled liner completion).
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