Formation Damage in Horizontal Wells

by
Bimal Thomas, MSE

University of Texas at Austin, 1997
Supervisor: Mukul M. Sharma

This thesis presents the results of an experimental study on the extent, depth, and distribution of mud induced formation damage around a horizontal wellbore. This investigation aims at addressing the question of how much damage is caused in the bottom, middle, and upper portions of the hole when a horizontal well is drilled.

Our experimental apparatus consists of a 5" diameter pipe rotating inside a 7" diameter pipe. Three core holders are placed at the top, middle and bottom of the simulated borehole. The fluid loss rate and the permeability of 4 different sections of the core are measured as mud is circulated in the annulus and the inside pipe is rotated. The formation damage and the fluid loss data for the top, middle and bottom of the wellbore are measured for different drill-in fluids, axial velocities and pipe rotation rates.

It is found that when the drill pipe is concentric the fluid loss rate is independent of axial fluid velocity and rotational speed of drill pipe. For eccentric annuli (as might be expected in horizontal wellbores) the extent of damage and fluid in the different cores are related to the speed of drill pipe rotation and the time of exposure to the mud. Erosion of the mud cake at the bottom of the hole plays an important role in the distribution of formation damage around the hole. The results of this investigation provide a better understanding of formation damage around horizontal boreholes.

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