Overview

Geomechanics tools are used to forecast, and then gauge, asset performance over time. Wellbore integrity, sand management, and frac-pack engineering design and execution practices are linked by characterizing the geological section in terms of rock mechanical properties. Often, seemingly unrelated events that can plague high-risk, high-cost developments can be understood best when the geological environment, the geology and geophysics, is described as an engineering material (i.e., the rock mechanical properties that include formation strength and stress). A consistent characterization of formation stress and strength with the geological structure, lithology, and seismic attributes used to recognize the prospect ensures that the explorationists’ vision is linked to the well engineers’ design.

Further, a consistent mechanical-property model for the field can be used to create a full-cycle asset-development plan from appraisal through abandonment, helping to reduce the risk of missed future opportunities resulting from well-systems-design constraints. Two examples come to mind.

Reservoir-pressure depletion and subsidence can affect borehole stability to the extent that complex well designs are necessary to exploit the asset fully. Well placement depends on the subsiding reservoir section and on the reaction of the overlying geological section that must be drilled through to reach the reservoir.
Sanding-potential risk usually increases with depletion. For compartmentalized reservoirs with varying depletion schedules, sand-risk mitigation often leads to one-size-fits-all completions that usually result in sand control. This method can limit re-entry options and decrease recovery. An accurate forecast of sanding tendencies for individual reservoirs, including the field production-management practices that affect sanding, can result in a more selective fit-for-purpose approach to completion design.
For land-based operations, the consequences of well complexity may be addressed more easily; the downside is a poor estimate of field recovery that can either reduce opportunities for outlying prospects or, in the worst case, cause the asset to seem uneconomic. For major-capital projects such as deepwater subsalt fields, the capital outlays are immense, with single wells costing U.S. $100 million. For these deepwater projects, it is required that fewer wells produce reliably for longer periods of time. Well engineers need to get it right the first time.

Sand Production in the Statfjord Field
High-Accuracy Oriented Perforating Extends Sand-Free Production Life of Andrew Field
Gravel Packing Long Horizontal Wells With Low Fracture Gradients

Harvey E. Goodman, SPE, is a staff research consultant for Chevron Energy Technology Co. His key technical responsibilities include rock physics and the application of geomechanics to well design by use of the common-Earth-model approach. Goodman served as an SPE Distinguished Lecturer for 2004–05 and serves on the JPT Editorial Committee. He earned BS and MS degrees in geological engineering from the U. of Missouri–Rolla.

Overview

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