Video: Distance-of-Investigation Could be Misused in Unconventional Heterogeneous Reservoirs with Non-Static Properties
- Bin Yuan (University of Calgary, Canada) | Zhenzihao Zhang (University of Calgary, Canada) | Christopher R. Clarkson (University of Calgary, Canada)
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- Society of Petroleum Engineers
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- 2018. Copyright is retained by the author. This presentation is distributed by SPE with the permission of the author. Contact the author for permission to use material from this video.
- 5.6.3 Pressure Transient Testing, 5 Reservoir Desciption & Dynamics, 5.6 Formation Evaluation & Management, 3 Production and Well Operations, 2 Well completion
- Resevoir Hetergeniety, Unconventional Reservoirs, Rate-Transient Analysis, Distance-of-Investigation, Reservoir Dynamics
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The concept of distance-of-investigation (DOI) has been widely applied in rate- and pressure-transient analysis for estimating reservoir properties and for hydraulic fracture optimization. Despite its successful application in conventional reservoirs, significant errors arise when extending the concept to unconventional reservoirs. This work aims to clearly demonstrate such errors in the use of the traditional square-root-of-time model for DOI calculations in unconventional reservoirs, and to develop new models to improve the DOI calculations.
In this work, the following mechanisms in unconventional reservoirs are first incorporated into the calculation of DOI: 1) pressure-dependency of rock and fluid properties; 2) continuous/discontinuous spatial variation of reservoir properties. To achieve this, pseudo-pressure, pseudo-time and pseudo-distance are introduced to linearize the diffusivity equation. Two novel methods are developed for calculating DOI, one using the concept of continuous succession of steady-states, and the other using the concept of dynamic-drainage-area (DDA). Both models are verified using a series of fine-grid numerical simulations. A production data analysis workflow using the new DOI models is proposed to analytically characterize reservoir heterogeneity and fracture properties.
The new DOI models compensate for the inability of the traditional square-root-of-time model to capture spatial and temporal variations of reservoir and fluid properties. The pressure-dependency of fluids and reservoir (i.e., fluid density, viscosity, rock permeability and porosity) and reservoir heterogeneities (i.e., deterioration of reservoir quality from the primary fracture to the reservoir), can significantly retard the propagation of the DOI. Another important outcome of this work is to provide a practical and analytical approach to estimate the spatial heterogeneity directly from the production history of field cases.