Fluid Placement Model for Stimulation of Horizontal or Variable Inclination Wells

by
Laura D. Eckerfield, MSE

University of Texas at Austin, 1999
Supervisor: A. Daniel Hill

Acidizing is a common method of stimulating horizontal wells. The acidizing process is fundamentally different when applied to a horizontal well as compared to application to a vertical well. The fluid distribution in a horizontal well is affected by a longer wellbore length, a broader variation in the reservoir properties along the wellbore, and possibly different mechanical means to place the fluids in the wellbore. A comprehensive fluid placement model linked with a reservoir acidizing simulator is essential to optimize the design of acidizing treatments for horizontal wells.

This report presents a model of fluid placement in a horizontal well. The model predicts the placement of injected fluids by tracking the interfaces between different fluids in the wellbore. It is capable of tracking multiple interfaces for multiple injection stages in horizontal wells. For injection with coiled tubing, the model allows tubing tail movement during injection. Simultaneous injection from the annulus and from a tubing string can also be simulated. A unique feature of the model is the consideration of gravity under-riding of the denser injected acid when the wellbore is deviated from horizontal. Both analytical and discretized solutions of the model are presented in this report. Examples in the paper illustrate the effects upon fluid placement resulting from such factors as velocity of tubing movement, annular injection, non-uniform flow rate distribution (along the horizontal wellbore section), and gravity segregation under-riding in inclined wellbore sections.

The wellbore placement model has been linked with a matrix acidizing model calculating damage dissolution and skin reduction near the wellbore. The simulator can lead to determination of optimal tubing tail locations and fluid injection volumes, and to select the most appropriate diverting methods; hence maximizing the benefits of an acidizing treatment.

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