Donald W. Lee

Predicting Reservoir Compaction and Casing Deformation in Deepwater Turbidites using a 3D Mechanical Earth Model

Production from deepwater turbidites is made more challenging by geomechanical problems arising from overpressure, reservoir compaction, casing failure, etc. The impact of reservoir compaction on field development is best examined early in the life of the field, when there is an opportunity for proactive planning. The interaction between heterogeneous reservoir layers, well trajectories and stress changes due to depletion is a complex 3D problem; it is best solved using a 3D approach. This paper illustrates the use of a 3D MEM (Mechanical Earth Model) to quantify reservoir compaction, casing failure and surface subsidence for a deepwater Gulf of Mexico turbidite. Reservoir flow simulation data are used to evaluate stress changes, reservoir compaction, casing deformation and surface subsidence resulting from production. Geomechanical hot spots, where reservoir compaction is predicted to be greatest, are identified to allow production strategy to be optimized. Several possible modes of production-induced casing failure are examined. The likelihood of casing failure is then assessed to facilitate development of strategies for either avoiding such risks, or reducing their impact. This work shows the importance of developing a 3D MEM early in field development. In high-porosity, pressurecompartmentalized sandstones, quantification of reservoir compaction is essential for planning the casing and completion integrity through the life of the reservoir. Introduction Many oilfield projects today are challenging because of geomechanical problems arising from overpressure, wellbore instability, reservoir compaction, casing failure, sanding, surface subsidence, fault reactivation, etc. The use of a 3D MEM allows all information related to the geomechanics of drilling and production to be captured, including in-situ stresses, rock failure mechanisms, rock mechanical parameters, geologic structure, stratigraphy and well geometry. Once constructed, this model can be used to identify geomechanical problems and to devise contingency plans for handling them before the well is drilled. The use of a 3D MEM for predicting reservoir compaction from pressure depletion, plus its associated impact on casing deformation and surface subsidence, is demonstrated for a complex turbidite reservoir. Fig. 1 shows the steps involved in building a 3D MEM, while Fig. 2 illustrates the construction of a 3D MEM using well logs and seismic horizons. Fig. 3 shows how the MEM may be updated using data acquired while drilling a well. Fig. 1 Steps involved in constructing a 3D MEM. Fig. 2 Construction of a 3D MEM. Well logs are combined with seismic horizons to build the model.