This paper shows how rock strength analysis can be utilized in preventing wellbore collapse and sand control problems during production of directional wells. From this study it is seen that selecting the correct production rate can avoid wellbore collapse which cause sand production. When the production rate is increased the reservoir drawdown near the wellbore cause an increase in the effective wellbore wall rock stresses. Using the von Mises rock failure criteria for wellbore stability analysis, the maximum production rate without formation collapse and sand production can be estimated. The parameters that effect the rock stresses at the borehole wall are the in-situ stresses, wellbore inclination and direction, and fluid pressure in the rock which is a function of the production rate. If the decrease in the near wellbore fluid pressure due to high production rate causes the effective stresses to exceed the failure criteria the wellbore will collapse to a certain new diameter. After the new diameter is estimated the volume of produced sand is calculated. The study concludes that possible sand production should be carefully analyzed in all directional wells. The wellbore sand production is a much more severe problem in directional wells and might limit the production rate. The maximum production rates with no sand production can be obtained using the approach in this paper.
Wellbore stability is extremely important for the success in drilling and production. Wellbore instability during drilling may cause stuck pipe, cementing problem, or drilling fluid loss which may cause in a blow out. Wellbore collapse occurs because of insufficient mud. Fig. 1 shows the types of collapse in the wellbore.
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