Current methodologies for drill planning, widely implemented by Oil Companiesto optimize the definition of technical and economic options for the drillingprocess, are based on a scrupulous analysis of the production requirements, thetechnical risks, and the geological uncertainties. Planning and designingdrilling projects begin by considering the problems observed in correlationwells drilled in the same field, in order to obtain a successful mechanicalmodel. Once the drilling process begins, an evaluation of the continuing operationsallows drilling engineers to control and adjust the differences that may arisebetween the drilling plan and the actual conditions observed while drilling. These identified variations are related to uncertainties in the criticaloperational parameters, such as pore pressure and fracture pressure gradients, salt intrusions, and changes in the planned lithology column, such as, shaledomes, and gas shows. Dealing with these variations is imperative, as they candetermine either the success or the failure of the well. This Paper proposes a Real-Time Drilling Engineering Methodology that allowsoperations staff to drill ahead in depth and time by anticipating geological, mechanical and operational conditions, thus allowing preemptive actions. ThisMethodology allows forecasting the adequate drilling parameters by visualizingthe current conditions of the well. These include the analysis of theinteraction between the drill string and the fluid with the formation, thenormalization of mud densities in the areas of interest, and the analysis ofgeopressures from logging-while-drilling data. Other parameters that need to beconsidered might include the variation of casing and hydraulics designs, andthe optimization of the well path from Real-Time Trajectory and Log Data. This Real-Time analysis leads to immediate engineering recommendations that caneliminate and avoid ongoing and potentially undesirable situations whiledrilling, such as stuck pipes, gasifications, and runoffs, thereby allowing apreemptive response to the variations that may occur between the proposeddrilling plan and the actual drilling conditions. By applying this Methodologyin several oilfields in Southern Mexico, an observed 20% increase of thetechnical efficiency of the drilling process has been reported, resulting inover 80% of the wells operating under normal conditions, with a reduction inthe average cost of the well for the operator.

The geological structures to drill and reach the producing reservoir of the South region of Mexico are very complex. They can vary from deep fractured carbonates reservoir at more than 7000 m true vertical depth, anticline uplifted by salt or/and shale dome themselves inducing abnormal pressure up to 2.2 gr/cc of equivalent density in the overlying formation. The geological complexity of the south region is reflected also in its geo-pressures, geo-stresses and geomechanical properties. Since early 2000 Petrόleos Mexicanos (PEMEX) has considered the Geomechanics discipline as a key component for their future economic success. With the urgent need to improve recovery, more complex wells are being drilled and PEMEX has taken the challenge to have geomechanics analysis for any well that will cost more than 10 Million of dollars. This strategy has been translated with training of key personnel, geomechanical core campaign and geomechanics studies included into their drilling program. Since 2006, more than fifty geomechanics studies (analytical and numerical) have been carried out in the south region of Mexico and have been incorporated to mitigate drilling risk and optimize well design. Velocity analysis, Geomechanics core test interpretation, caving interpretation, breakouts and induced fracture analysis from image logs, direct pressure measurements, leak off test and mini-frac interpretation are some of the different information used to calibrate the geomechanics studies. This paper refers to the regional compilation, findings and results of the 50 geomechanics studies conducted in the different fields of the south region between 2006 and 2010 and its impact on the well design of exploratory and development locations. The paper presents to the industry, the methodology used for their construction, illustrated by the data used for their calibration and how they were successfully used for well design and real time decision with selected post mortem analysis for some well. Finally the results of the geomechanical studies (Strength, overpressure and stress anisotropy) have been mapped regionally to forecast the geomechanics behavior in the entire south region of Mexico to optimize the drilling of future well locations.

Borehole instability mechanisms have been studied in oilwell drilling for many years. Rock behavior has been important because drilling complexity and risk increase accordingly, leading to the need of more complete risk assessments in well design. A new need for risk assessment arises in South Mexico where Pemex and Schlumberger have encountered very challenging areas: a depositional HPHT environment with salt presence, faulted formations, and depleted reservoirs resulting in high-risk wellbores. In strong dipping formations, wellbore instability occurred as a result of planes of weakness. Several events that resulted in stuck pipe due to packing off, losing wellbore sections and downhole tools translated into severe financial impact. Planes of weakness are directly related to the well's trajectory. Developing a method was needed to predict the attack angle - during the design phase. An erroneous appreciation of the instability mechanism could lead to wrong actions, like increasing the mud density without additional considerations, making problems worse. Using surface seismic readings and attributes resulted in successfully predicting wellbore instability caused by planes of weakness. The signal-to-noise ratio of a seismic survey was enhanced. Attributes were applied to get an improved structural continuity with reliable dip/azimuth results. An innovative methodology to calculate the attack angle from dip/azimuth from seismic and associated risks of wellbore instability was developed. Three wells drilled in a complex structure affected by a compressive salt environment were evaluated and compared to well logs, getting a good fit. A complete risk assessment includes the calculation of the attack angle, fault mapping, and rock strength. Knowing these allows for a more complete trajectory planning while predicting wellbore instability. Thus, the output provides a valuable tool to predict failure caused by planes of weakness in the design phase, allowing trajectory modification and operational prevention/mitigation measures to avoid catastrophic stuck pipe incidents and achieve a hazard-free well construction.

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.

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