| Abstract |
One of the major drilling sefbacks encountered by PNOC-EDC when drilling infill wells is interference. This /s either the direct invasion of drilling fluids and/or cement into, or the thermal degradation af, adjacent production wells while drilling resulting to output reduction or, worst, permanent damage. Consequently, the well being drilled is prematurely terminated. The Underbalanced Drilling (UBD) was used to address interference while drilling. This ,'s drilling with the hydrostatic head of the drilling fluid lower than formation pressure. This permits flow towards the well instead of the drilling fluid or cement interfering with adjacent wells. ln our application, we used the aerated fluid sysfem wherein air is added to the liquid phase of the drilling fluid to lighten the effective mud weight. The UBD was applied on Wells 422D, 315D and 421D in our Leyte Geothermal Production Field. The results were very positive as the technology success fully addressedi nterferencep roblemso n infill wells. Other than drilling pasf the zones with inbrterence potentials, we were a/so able to drill to the desired programmed depth which ,s within the liquid section of the geothermal reseruoir. While total suspended so/ids (ISS/ fluctuations were obserued during drilling, they were insignificant to neither reduce plant output nor create permanent damage to the adjacent wells. The cosf evaluation a/so showed that the UBD ,s still economical against our conventional drilling when applied to infill wells. |