Samaria field in southern Mexico is one of the oldest light oil producers. Reservoir pressures can be classified as highly depleted in cretaceous, the use of nitrogen injection thru the drill pipe to lighten the mud column is a common practice to reach low equivalent circulating densities and avoid massive loss circulation and related hole cleaning problems. Large amounts of nitrogen injection rates are also a common scenario in this specific field many times reaching the technical limit of a multiphase Managed Pressure Drilling application avoiding the friction dominated side of pressure curves. Natural tendency to achieve more production is to drill horizontal wells as demonstrated by the production results of a number of attempts made in the past. However, the presence of high N2 injection rates thru the drill pipe represents a serious challenge for measuring and logging while drilling pulse type downhole tools frustrating the possibility of achieving a full directional control in the reservoir section. Dowhole temperatures are also higher than conventional drilling because of the presence of high gas vs liquid ratios, reaching very fast the technology limits. This document presents the engineering process, planning and design for the drilling with concentric casing nitrogen injection technique in a horizontal well with directional control in real time, into a low pressure reservoir. The technique allowed building up and correcting the well trajectory successfully reaching the proposed targets. (Horizontal length, Drain Area) The steady stable and transient simulations to validate stabilization are also presented along with the final results in terms of production and skin damage. Introduction The well presented in this document belongs to the Bermudez Complex (Samaria Field) located in the south the Mexico as shown in Figure 1. The reservoir is formed by carbonates and dolomites from upper, Medium and Lower Cretaceous at vertical depths ranging between 4200 m - 4500 m. The original reservoir pressure was originally equivalent to 1,3 gr/cc (7500 psi), however because of the production rates and exploitation time, today's formation pressure is around 2200 psi (0,4 gr/cc), about 30 % of the original pressure. Because of the actual low reservoir pressure and typical problems associated with it (loss circulation, Differential sticking). The near balance technique using multiphase fluids (nitrified) was implemented. This technique was the right solution but was limited to vertical and low angle wells, mainly because high nitrogen volumes attenuate the MWD telemetry through Drill pipe, therefore neither tool face nor formation evaluation data, can be obtained while drilling in order to steer within reservoir. The high Gas/Liquid Ratio used with large amounts of the N2 injected to avoid mud looses, caused the annular temperature around directional tools to increase rapidly, above 150 C, as friction increases with the drill pipe rotation, generation electronic failures. Additionally N2 gas penetrates the motor stator eleastomer at certain temperature and pressure conditions causing dohwnhole motor elastomers failures. These limitations condemned most of the high angle wells to be drilled "blind" with conventional assemblies where neither directional control nor formation evaluation data was delivered in real time or memory format. This situation was of course a huge technical limitation for the operator which requires both service on this field and ones that have similar environments to increase production rates. Wired Drill pipe Technology was tested in a similar field, however very low N2 volume were injected compared to ones that are currently used in the Samaria field. During the well execution several tool failures were reported in wired rotary steerable systems, mostly associated to high temperatures.

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.