Abstract

Beginning in the early 1990's, Chevron (CVX) initiated the strategy of developing mechanical earth models from acoustics dominated data volumes. The business driver was to link the G&G disciplines involved with prospect exploration and development with the engineering disciplines involved in well systems design. This strategy has culminated in CVX's capability to build Mechanical Earth Models (MEM) from the reservoir to surface, linking earth physical properties, i.e., rheology, to the geology, seismic geophysics and in situ stress character of the entire geologic section. MEMs are now being created during early project stages, to provide a phased approach to asses well systems design risk. Well planners now use MEM volumes for bit optimization & performance prediction, wellbore stability, sand prediction, fracture stimulation design, cuttings disposal design and seismic reservoir characterization for by-passed oil. The presentation will introduce acoustics based rock mechanics concepts, describe CVX's acoustics based rock property prediction technique, and present field application case histories for selected business units world-wide, including deepwater Gulf of Mexico, North Sea, the Arabian Gulf, offshore West Africa and Asia.

Introduction

Key components of a Mechanical Earth Model (MEM) critical to well systems are shown in Figure 1. The calibration process creates a consistent set of earth properties that define rock strength and stress. Agreement must be achieved between the rock physics or stiffness, the geological model (lithology and structural style), drilling performance (pore pressure, rock strength, near wellbore stress), production and reservoir engineering attributes (stress measurements from hydraulic fracturing, compaction with depletion) and core measurements.

Figure 2 depicts the MEM central to some key technical applications involved in oil & gas asset development. The central graphic shows dynamic Poisson's ratio extracted from the 3D seismic based MEM. This GOCAD rendition (Geologic Object CAD) of Poisson's ratio is one of several MEM attributes that are used to design a well plan anywhere in the data volume, e.g., others include compressive strength, and dynamic & static elastic moduli.

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