Tecominoacan 408: First Underbalance Drilling Application in Mexico
Authors: Maclovio Yanez M. , Martin Valenzuela J. 
Published: December 2007

Abstract
In Mexico, important volumes of oil are found in partially depleted reservoirs, whose exploitation presents problems that most be faced with advanced techniques. Here it is described the first underbalance drilling full application in Mexico, which allowed to drill a 19,000 ft producing well, showing that investments in head technology, engineering research and personnel training, are justified since they increase the probability of success while drilling the well and decrease the production costs.

Introduction
Oil well drilling faces new challenges due to the change of pressure conditions that are observed in large number of reservoirs, which leads to the application of advanced techniques to reach the objectives. Underbalance drilling is a great potential technique particularly in depleted wells, like Tecominoacan 408, where a solution was given to total lost circulation and drilling string sticking problems, which would be uncontrollable under conventional techniques that would have demanded large amounts of supplies, time, high cost and, over all, the low probability of success. Like in any other activity, the key of success is to foresee the expected problems, which can be achieved through an smart planning that considers the implementation of head technology, as well as the resolved involvement of the operative, technical and administrative personnel. It is indispensable to count with technological support for the surface separating equipment selection, fluids handling, the top-drive use, nitrogen injection to establish circulation, so as with the intercourse of external and internal experiences on the subject. Understanding the applied principles, as well as the geological petroleum knowledge of the reservoir and the formations to drill through, is likely important since this contributed to achieve the first Mexico's producing well realized with full Underbalance Drilling technique.

Background
This chapter exposes the geological and exploitation background which has led Tho-Tecominoacan Field to its current situation, and what it is expected to obtain through the effort to accomplish detailed studies of the reservoir by creating multidisciplinary groups to optimize the exploitation.
The Jujo-Tecontinoacan Field, with its 18,000 acres, is one of the main light-oil producers, and one of the most important fields in Mexico. Located within the Cardenas and Huimanguillo counties, in Tabasco state, an area of large socioeconomic activity (fig. 1), its exploitation is developed in harmonic coexistence with the beautiful ecosystem, cattle- raising, agriculture, and the small industries dedicated to the transformation and services, at the numerous communities of the region. Due to its importance, it has been submitted to seismic, geological, reservoir characterization and numeric simulation, fluids-phase behavior and some other studies through a multidisciplinary group integrated by elements from the Reservoirs, Exploration, Production, Drilling and some other areas, which has been in charge of realizing studies and managing its exploitation.
In terms of Geology, it is situated inside the Mesozoic Chiapas-Tabasco area, at the limits of the Comalcalco and Macuspana Basins, as a product of the Laramide Orogeny, towards the Late Oligocene or Early Miocene 70 million years ago, a horst was formed which raised the storage rocks from the Upper Kimmeridgian and Tithonian Jurassic and from the Lower Cretaceous, in an anticline asymmetric structure that actually has its axial axis orientated NW-SE, and it inclines to the NE (fig. 2), with evidence of sedimentary regression environment.
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