WELL-BORE COMPLETION TECHNIQUE AND GEOTECHNICAL PARAMETERS INFLUENCING GAS-PRODUCTION

A methodology is proposed for cost-effective improvement of oil and ga s production from existing and new reservoirs. Using established geome chanical concepts it can be shown that in reservoirs with low strength characteristics, oil and gas production can be enhanced several fold if cavitation can be induced around the well bore within the pay zone. Creation of the well bore results in a plastic zone, the size of whic h increases with decreased strength properties. Permeability within th e plastic zone can increase as a result of a reduction in the mean eff ective stress level and shear-induced dilation. Further enlargement of the cavity, for instance, by applying cycles of pressure buildup and rapid drawdown, results in a corresponding expansion of the plastic zo ne with a concomitant increase in the size of the enhanced permeabilit y region. A fully coupled fluid flow and effective stress finite eleme nt model is used to study the factors that influence well-bore cavitat ion and fluid production. This model has shown that an open-hole cavit y completion technique outperforms other alternative methods, such as fracturing, if the formation has low strength characteristics. Product ion performance in competent rocks, however, will suffer from cavitati on because of the development of(1) a relatively tight plastic zone, a nd (2) a large zone of reduced permeability outside the plastic zone. The proposed model has been used to analyze a field problem involving a well bore that experienced a fourfold increase in production as a re sult of cavity enlargement. As both the increase in flow rate and the size of failure were satisfactorily matched, it can be considered that the parameters selected were representative and the modelling was rea listic.