Case history of an opposed-bore, dual horizontal well in the Austin Chalk formation of South Texas

Petro-Hunt Corp. used a unique horizontal-well design to optimize development of an irregularly shaped lease in the Austin Chalk formation in Texas. Two medium-radius horizontal bores were drilled in opposite directions from one vertical hole to maximize horizontal displacement in the lease. Underbalanced drilling techniques were used to prevent formation damage. The well design resulted in a significant cost savings per horizontal foot compared with 24 offset wells that the operator drilled. This paper reviews well planning and drilling and emphasizes techniques used to intersect thin horizontal targets and to initiate the second horizontal bore. Production results and drilling economics are discussed briefly, and ideas on future dual-horizontal-well applications are presented.