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Analysis of Development Methods for Gravel Envelope Wells
Analysis of Development Methods for Gravel Envelope Wells Imprimir
Viernes, 14 de Enero de 2011 14:55

E. John List, Ph.D.


E. John List, a native of New Zealand is a graduate of the University of Auckland. In 1965 he was awarded a Ph.D. in Applied Mechanics and Mathematics from the California Institute of Technology.


Following a year as a resident fellow at Caltech he returned to the University of Auckland as a senior lecturer in Theoretical and Applied Mechanics. Since 1969 Dr. List has served on the faculty of Caltech in various capacities. Currently he is the professor and executive officer of environmental engineering sciences. His academic interests include hydrodynamics, analysis of pressure transients, and flows through porous media.

Summary

Five basic techniques of well development have been studied. The purpose of the investigation was to provide a quantitative basis for evaluating the relative efficiency of respective development methods in gravel envelope wells. The techniques evaluated were:
·  jetting
·  line swabbing
·  rocker beam swabbing
·  single swab mounted on drill pipe with simultaneous injection below the swab
·  double swabs mounted on drill pipe with injection between the swabs.

The analysis assumed a completed well with a filter pack between the screen and the aquifer. The primary goal of the studies performed was determination of the direction and magnitude of the flow velocity field at the pack/ formation interface. Evaluation of this flow velocity distribution gives clear indication of the ability of the development techniques to clean drilling debris and wall cake from the formation. Results of the study indicate that both swabbing and jetting can be effective development mehods for gravel envelope wells. Swabbing methods involving pumping appear to offer even further benefits. The efficiency of jetting techniques is found to be conditional on use of a filter pack size distribution that will enable filter particle circulation to develop. In the absence of this circulation, jetting is likely to be of limited use.

 

INTRODUCTION

Constructing of gravel envelope wells by the hydraulic rotary drilling system requires circulation of a drilling fluid in order to remove drilled cuttings from the borehole, lubricate the drill string and bit, provide sufficient hydrostatic pressure to overbalance formation pressures and deposit a thin impervious filter cake on the borehole wall. This mud system along with residual solids remaining in the borehole will reduce well capacity significantly unless removed prior to production.

The process of development first requires that these drilling byproducts be removed from the interface between the borehole and the filter pack in order that final development, which consists of removal of fine materials from the aquifers and stabilization of pack-aquifer materials around the well screen, can be carried out. Preliminary development of gravel envelope wells normally consists of various combinations of circulating, swabbing, jetting, and other methods of conditioning filter pack prior to installation of a turbine development pump.

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