Cazares-Robles, Francisco (Pemex E&P) | Corbala, Marco Corona (Pemex) | Monroy, Rafael R. (Pemex) | Kulakofsky, David S. (Halliburton Co.) | Caballero, Carlos (Halliburton de Mexico, S.A. de C.V.) | Rivera, Jorge Alberto (Halliburton de Mexico, S.A. de C.V.)
Oil reservoir depletion resulting from commercial exploitation of mature fields has increased the frequency of special drilling conditions caused by low formation pressures that can lead to massive drilling fluid losses. Several of these challenges have been addressed by cementation engineering, specifically applied to the production casing.
Because of these conditions, the Antonio J. Bermúdez basin has been constantly evolving with regard to cementing technology as well as drilling fluids concerns in an effort to effectively obtain long term zonal isolation.
Application of cementation engineering for production casing in development fields has resulted in the need for low-density slurries that can rapidly develop compressive strength. Furthermore, improvement in rock mechanics understanding using formation-evaluation technologies, has positioned cementation engineering as a technical discipline focused on application of solutions encompassing the entire life of the well. As a result, for example, the concepts of elasticity and durability have become important for cementation engineering, which is now moving far beyond the traditional application of hydraulic principles for slurry design.
This paper describes the evolution and maturing of the Antonio J. Bermúdez Basin during the past ten years and the changes in design and execution of cementing operations as a result of new challenges in oil-based and water-based mud environments as well as the introduction of under-balanced drilling methods.
The Antonio J. Bermúdez complex is located in southern Mexico in the states of Tabasco and Chiapas (Fig. 1). The reservoir has a history of exploitation dating from the 1930s, producing from multiple zones of fractured and vugular carbonates derived from geological events that caused the Jurassic Gulf of Mexico opening in the late Triassic to late Jurassic periods. With the onset of the break up of Pangaea (Fig. 2), where redbeds, volcanics, and salt were deposited in a system of rifts, the marine deposition environment is the source of most oil and gas reservoir rocks (carbonates and dolomites) in the Bermúdez complex, massive erosion caused a diversified high- to low-permeability distribution, along the breccia trend. This complex composed basically by Samaria-Iride giant oilfields, Oxiacaque and Cunduacan, principally exploits reservoirs of light crude oil contained in limestone deposits and naturally fractured limestone and dolomite. Typical reservoir characteristics are shown in Table 1.
As a consequence of their exploitation, these deposits have experienced, during their life cycle, different phases that have created cementing and engineering challenges. Starting with a highly pressurized reservoir that required normal density slurries to the ultra-light density foamed slurries with densities as low as 0.6 sg required in some areas today. Not only does the pressure change in the reservoir, but also well depth and geometry, bottomhole flowing pressure, lifting technique from natural to gas lift, water-oil contact, fluid viscosity as it moves closer to the bubble point, stimulation, completion, and workover techniques and pressure testing methods.
All of these changing factors are directly related to the evolution of cementing engineering to efficiently exploit this reservoir, applying a methodology that studies the sequences of events over the life of the Bermúdez complex oil wells, integrating new knowledge and applying new technologies, correcting and adjusting previous knowledge, gathering observable, empirical, and measurable evidence, focusing not only in cement slurry design as was done in the past but an integrated engineering process to understand the challenges that change over time and address them in consequence, including key performance indicators, well challenges, objectives, best practices, scorecards, material selections, testing, job planning, execution, QA/QC, and post-job evaluation, integrating a proven methodology that, if applied, will consistently help lead to obtaining an effective annular seal over the life of the well.