Multiple operators had attempted to conventionally drill wells in an area of south Texas targeting an over pressurized sand. A majority of them were unsuccessful showing a history of lost time events and poor well results related to kicks and losses. Information suggests little was known about the pore and fracture pressure gradients, and that uncertainties regarding real stratigraphic distribution were present, resulting in improper casing points and mud trends not in accordance with actual wells requirements. For these reasons, one operator decided to implement Managed Pressure Drilling (MPD) technology in order to safely and efficiently drill a well to the pay zone.
The scope of the operation was a re-entry sidetrack on a vertical well that originally encountered well control and multiple mud losses events. The first interval was an 8-1/2 inch intermediate section to be cased with a 7 inch liner. The liner shoe was to be set approximately 80 feet above the over pressurized target sand. The second interval was a 6-1/8 inch production section targeting the well pay zone, to be cased with a 4-1/2 inch production casing. Both intervals were considered critical, the first one having depleted zones interbedded with gas bearing formations with a final depth immediate to abnormal gas pressures, and the second demanding accurate ECD management to avoid well control events, losses and formation damage, this of cardinal interest for the operator.
The implementation of MPD enabled both intervals to be drilled to the planned target in a constant bottom hole pressure (CBHP) state safely and efficiently. The well was drilled near balanced to improve drilling efficiency and increase the ability to identify pore pressures. The annular pressure profile was adjusted instantly as the well dictated by means of MPD surface equipment avoiding kicks and losses. Continuous evaluation and monitoring of well behavior in real time allowed for pore pressure predictions, which were later used to plan proper kill mud weights, tripping/stripping procedures, and managed pressure cementing operations. Implementing MPD techniques and technology proved successful in enhancing safety and drilling efficiency on a well with many uncertainties and potential hazards.
This paper will describe the planning and execution of a successful drilling operation on a high potential oil/gas producer well using MPD techniques in an area where others were unsuccessful.