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.

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractThe majority of the fields in southeast Mexico require 1,000m to 3,400m of 17-1/2 hole to set 13-3/8 casing at the top of Encanto/Deposito formation. Lithology is typically weak sandstone with shale stringers (UCS 2,000-6,000 psi). Operators have attempted to use PDC to drill the hole section in one run with limited success. Operators required an updated steel-tooth rollercone to cut costs by reducing trips/bits to complete the section. Examination of steel-tooth dulls indicated erosive and abrasive wear due to the high sand content was the major factor limiting performance improvement.The authors will present case studies that document the new bit design has increased meterage by at least 46%, ROP by 12%. Total bit runs have decreased from six to four and the total cone revolutions have increased by 60% compared to average values of best offset runs in several fields. This has saved the operator an average of $140,000USD per 17-1/2" hole section per well.

This paper will focus on design, planning and execution process followed to apply managed pressure drilling (MPD) using a Concentric Casing nitrogen Injection to drill a high angle well in a fractured carbonate mature field. It will be shown how steady state multiphase flow modeling was used to find operating envelope in terms of ECD and hole cleaning and transient flow simulations to predict and select the best parameters to avoid well slugging and pressure instability. Formation pressure of this flied have been decreasing over the last 25 years with current values down to 0.4 g/cm3 SG. During the previous years, MPD techniques had been implemented using Nitrogen injected through Drill Pipe to overcome operational problems like mud lost circulation and differential sticking. However the high volume of nitrogen inside the drill pipe generates important limitations for conventional MWD tools, but also the use of Electromagnetic tools has limitations in some cases due to high bottom hole temperature or formations resistivity. This situation has restricted the implementation of high angle and horizontal drilling due to reduced possibility to control the trajectory to reach the target in this kind of wells. Three horizontal wells have been previously drilled in this field without very good results. Nevertheless, horizontal wells are required in order to keep the production level above the forecasted declination. Intelligent drill pipe appeared as another option, but also the tools still will be affected by temperature with gasified system. The nitrogen concentric injection technique was analyzed as a solution to make feasible the use of conventional mud pulse MWD/LWD tools and keeping at the same time bottom holes circulating pressures within the operational window required to avoid circulation losses, assure good hole cleaning and control risk of hole instability. Once it was determined the feasibility of this technical option, extensive planning sessions were carried out to design specific operational procedures for this application. It was based on steady state and transient flow modeling assuming different operational parameters to evaluate the expected performance of the operation. Exhaustive Risk Analysis and rigorous class room and rig site training were developed to make all the personnel involved in the operation familiar with the desired understanding of the project. Introduction In terms of oil production, the Complex Antonio J. Bermudez is the greatest producer of the southern region and the fourth greatest of Mexico. This complex includes the fields Samaria, Cunduacan, Oxiacaque, Iride, Platanal and Carrizo and covers a total area of 192 square kilometers. The well discoverer of this Bermudez Complex was the Samaria-2, which was drilled in 1960, but it was only until 1973 when the potential of the field was confirmed with the drilling of the Samaria-101 Well. The Samaria field is located in what is geologically known as the Southeastern Basin and it is specifically within the Chiapas-Tabasco area at 20 kilometers from Villahermosa, Tabasco, Mexico; as show in Figure 1.

Samaria oilfield, located in southern Mexico 20 km west of Villahermosa, Tabasco, with an area of about 160 km2 is one of the world's largest in extension and one of the oldest oilfields in Mexico, historic crude oil exploitation targets the Cretaceous Upper Medium and Lower (4200 mts TVD to 4500 mts TVD). Formation pressure in these naturally fractured carbonates has been decreasing over the last 20 years with current values down to 0.4 gr/cc. Managed Pressure Drilling (MPD) techniques are implemented using Nitrogen injected through Drill Pipe to avoid lost circulation, formation damage and differential sticking. However the significant amount of nitrogen inside the DP generates important limitations for current MWD tools. The need for Horizontal wells to increase the drainage area has become a priority for the Mexican National oil company thus directional control and LWD capabilities must be prioritized. The nitrogen concentric injection technique was then taken into consideration to bring solutions to the MWD pulse signal transmission and downhole temperature handicaps. This paper describes the experience gained in planning and executing the first horizontal well in the Samaria field using Nitrogen Concentric String injection also recorded as the deepest ever concentric injection point (4171 mts MD and 4117 mts TVD). The paper will guide the technical community over the design, planning and execution process: geological review and candidate selection, pre-engineering study, transient and steady state multiphase flow modeling, final drilling program, training, safety, contingencies, directional planning for geo-steering with MWD/LWD, lessons learned and production enhancement results. Introduction Antonio J Bermúdez complex was discovered back in 1973. It produces from carbonates sequences from Mesozoic, Cretaceous and Jurassic ages and has been divided into five fields: Samaria, Cunduacan, Iride, Oxiacaque y Platanal and approximately 64 faulted blocks. Figure 1 shows the geographic location of the complex A. J. Bermúdez. Up to date, 342 wells have been drilled to Mesozoic formations and 90 wells to Tertiary. Currently 105 wells are producing from Mesozoic and 4 from Tertiary for a total of 145,194 BOPD and 310 MMSCF. Recently, in the SAMARIA field several projects have been carried out in order to improve productivity by drilling horizontal wells in low pressure (depleted) formations. Being a mature field, SAMARIA production reservoirs pressure average 0.40 gr/cc in highly fractured carbonates. An additional constraint is the rise of the WOC. In this scenario, drilling horizontal wells is a good opportunity to optimize production reducing the chances for water conning. On the other hand, current conditions of the field represent a technological challenge for horizontal drilling due to the difficulties to keep directional control (down hole tools communications) thru these depleted highly fractured reservoirs.

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractThe majority of the fields in southeast Mexico require 1,000m to 3,400m of 17-1/2 hole to set 13-3/8 casing at the top of Encanto/Deposito formation. Lithology is typically weak sandstone with shale stringers (UCS 2,000-6,000 psi). Operators have attempted to use PDC to drill the hole section in one run with limited success. Operators required an updated steel-tooth rollercone to cut costs by reducing trips/bits to complete the section. Examination of steel-tooth dulls indicated erosive and abrasive wear due to the high sand content was the major factor limiting performance improvement.The authors will present case studies that document the new bit design has increased meterage by at least 46%, ROP by 12%. Total bit runs have decreased from six to four and the total cone revolutions have increased by 60% compared to average values of best offset runs in several fields. This has saved the operator an average of $140,000USD per 17-1/2" hole section per well.