Underbalanced Drilling

Underbalanced horizontal drilling improves productivity in Hugoton field

How an operator increased production, extended well life and prevented drilling fluid loss in shallow, low-pressure gas wells

 Tijuana Devaul, BP America Production Co.; and Alejandro Coy, Weatherford International

 Hugoton field, located in the Texas Panhandle, is one of the largest gas producers in the Lower-48 states. These shallow reserves have been exploited by drilling either vertical wells with air or long-reach horizontal wells with conventional overbalanced techniques. Due to low formation pressures – in the 600 psi range – depletion is a major issue. Wells drilled in overbalanced mode have not exhibited a consistent productivity trend. 

 These low pressures have also resulted in severe lost circulation problems during drilling, with resultant formation damage and productivity deterioration. An additional challenge has been the close proximity of water to the productive formation, which effectively eliminates fracturing as a stimulation option. 

 Previously, wells were drilled vertically underbalanced, but the limited kh that resulted had little positive effect on productivity. Nevertheless, the operator decided to UBD three horizontal wells, as a case study to make a definitive evaluation of its effectiveness. All three wells were successfully completed and achieved a significant production increase, compared to offset wells drilled conventionally. The results achieved were of added significance considering the low-cost environment in which the wells were drilled, where conventional techniques typically produced marginal economics. 

 Detailed well design and UB models were considered, which took into account geological, reservoir depletion and water-proximity challenges. A detailed evaluation of incremental production rates of 300% to 400%, compared to offset wells drilled/completed conventionally, was also carried out.