The first commercial discovery of oil in Mexico took place in 1904, with the Pez-1 well located in the area of Ébano, San Luis Potosí. This well produced 1,500 barrels per day of crude oil. At the time, any well producing one tenth of this production was considered a great findthroughout the world.

Conventional overbalanced techniques were used to drill oil and gas wells in Mexico to control reservoir pressures and the mechanical stability of rocks where different formations intersected. It wasn’t until 1995 that PEMEX began to implement near/underbalanced drilling (UBD) techniques with the primary intent of drilling depleted reservoirs. Later on, managed pressure drilling (MPD) was implemented as a solution in several of the Mexico oil pay zones to overcome operational problems such as fluid losses, differential sticking, and influx events induced not only by the narrow margin operating window, but also the high frictional pressure losses due to increasingly complex wellbore geometries. Years ago, these hole sections were drilled conventionally, but the constant influxes and subsequent partial and/or total losses of circulation during the well control events made feasible alternative techniques mandatory to reach section TD without influx/loss events.

Single and multi-phase MPD techniques are now widely used across most all Mexico fields and have become a standard in well operations, unlike a few years ago when the technology was considered new. These techniques are used effectively to overcome operational problems in high pressure, high temperature (HPHT), high pressure, low temperature (HPLT) and low pressure, high temperature (LPHT) wells in deep reservoirs, delivering success by avoiding NPT and by successfully reaching planned TD.

Today Mexico is encountering a stage of MPD deployment that involves the use of state-of-the-art single andmulti-phase MPD techniques and UBD. Combined with dedicated engineering support, this approach has provided an increased level of safety and performance, and in some cases, allowed realtime formation evaluation through bottomholeprecise bottomhole pressure management with surface backpressure and nitrogen gas injection systems.

This paper summarizes the single and multi-phase MPD and UBD techniques performed on more than 400 complex and diverse hole sections in Mexico oil and gas basins, both exploration and development fields. Highly complex, specialized applications, such as foamed mud and concentric casing nitrogen injection drilling, will also be discussed.

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