Summary
In this paper, we present a new approach for modeling filtrate invasion
during the drilling of a horizontal well through regions with high-permeability
contrasts, such as those caused by fractures and high-permeability streaks, and
the impact that the cleanup of this approach has on well performance. The
approach incorporates the drilling schedule and experiment-based dynamic
filtrate-loss data into a fine-grid multiphase reservoir simulator. Unlike the
traditional leakoff model, which assumes piston-like displacement in the
filtrate-invaded zone, fluid flow in the invaded and the reservoir zones is
described by the use of more-realistic two-phase water/gas flow equations. The
equations are solved under the dynamic boundary conditions of the leakoff model
and time-varying reservoir exposure from drilling, tripping, completions, and
work-overs. Because the impact of fractures on both invasion and flowback is
more pronounced in low-permeability (tight) formations, the focus of this paper
is on such formations.
In overbalanced drilling, the initial dynamic mudcake formation is critical
in controlling filtrate loss. A dynamic fluid-loss model, which reflects the
spurt loss and non-Darcy and non-Newtonian characteristics of filtrate flow
through the mudcake is coupled with the reservoir simulator. Mud properties and
different events during drilling influence compression, dynamic deposition, and
erosion of the mudcake. The application of the dynamic filtrate-loss model
avoids the complexity in building a multiparameter mathematical mudcake model
without loss of generality. As in previous work, parameters in the dynamic
filtrate-loss model are based on special core tests.
In existing experiments, leakoff coefficients are measured only for the
matrix. The extrapolation of the dynamic leakoff coefficients for simulation of
fluid loss into intersecting fractures is discussed. Driven by Buckley-Leverett
equations, theoretical analysis is presented to emphasize the quantitatively
spatial correlation between the invaded-filtrate saturation and the spatial
permeability reduction in the invaded zone. The influence of water blocking,
relative permeability alteration, and damaged permeability variation on well
performance is simulated. A horizontal-well example is used to illustrate the
flexibility of this approach, and the results are discussed in the context of
well performance.
© 2009. Society of Petroleum Engineers
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History
- Original manuscript received:
3 August 2007
- Meeting paper published:
11 November 2007
- Revised manuscript received:
30 June 2009
- Manuscript approved:
2 July 2009
- Published online:
17 December 2009
- Version of record:
31 December 2009
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