MPD Concentric Nitrogen Injection Used to Drill a Successful Horizontal Well in Fractured and Depleted Mature Reservoir in Mexico South Region

Abstract

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.