ABSTRACT

McAllen Ranch is a prolific gas field located in Hidalgo County, Texas, that for several months in late 1997 to early 1998 was Texaco's biggest gas field worldwide with production reaching 165 MMCFGPD. Present production is about 60 MMCFPD, and the drop-off is attributed to renewed casing failures beginning in early 1998. All operators in the McAllen Ranch Field have experienced casing failures in the lower Vicksburg with up to 10% of active Vicksburg wells lost each year to casing failure. During 1997-1998, out of 18 ChevronTexaco Vicksburg wells drilled, eight experienced casing damage and six wellbores were lost. The loss of several high-rate wells resulted in the formation of a multi-disciplinary team to re-visit the casing failure problem. Engineering research involved the compilation of failure statistics, investigation of sulfide stress corrosion cracking, mechanical integrity of the casing design, and drilling practices. Geological research involved the construction of fault/failure maps, reasons for casing failures, and the retrieval of whole core sections across two productive Vicksburg sand/shale interface in Texaco's Guerra No. 68 for mechanical testing and rock analysis. Recommendations include engineering practice changes such as the management of reservoir depletion limiting drawdown in the early life of a new well allowing for stabilization of the well, and the elimination of ballooning during drilling/completion operations. Geological recommendations include the construction of subsurface geotechnical "hazard" maps, keyed to the sequence stratigraphy, showing where faults exist and where lithology-dependent slippage is of greatest risk. These maps could lower the risk of well failure by improved well placement resulting in significant savings.