One of the components in PEMEX's strategy to offset the natural decline of some of Mexico's giant fields consists in the implementation of technological advances and best practices for mature fields. About 70% of the hydrocarbon produced in Mexico originates in naturally fractured, depleted carbonate reservoirs, with active aquifers and secondary gas caps, which makes it difficult to maintain production levels and increase recovery factors. To optimize the reservoir-well-facilities systems, in 2006 PEMEX established, in cooperation with service companies, multidisciplinary productivity teams to generate portfolios of opportunities in all its production assets nationwide. The selection and optimization of stimulation and matrix-acidizing treatments were identified as critical enablers for production enhancement.
The stimulation designs have evolved in several directions, including the utilization of energized fluids, the introduction of emulsified acids, and the application of high-dissolution systems for high-temperature wells. Fluid placement techniques for selective stimulation have improved with the assistance of high-hydraulic-impact tools, inflatable packers, downhole real-time monitoring, and chemical-mechanical self-diverting fluids with degradable fibers to treat high-temperature formations. These improvements and evolutions have brought about solutions to historical problems and made it possible to optimize stimulation treatments in complex carbonate reservoirs with superior production results, including: 1) identifying natural-fracture patterns in low-productivity areas to increase the well-formation contact by acid fracturing; 2) treating and optimizing wells with severe gas breakthrough with strong diversion mechanisms to temporarily isolate the gas channels and stimulate the producing zones; 3) employing selective diversion fluids and non-reactive systems to break emulsions and water blockages in wells with high water cuts; and 4) applying state-of-the art fluids to maximize productivity from new discoveries.
The application of PEMEX's Well Productivity strategy is successfully contributing to maintaining Mexico's hydrocarbon production levels. For example, in PEMEX's South Region, it is estimated that 50,000 BOPD is the average incremental production per year obtained by solving a historical scale and organics deposition problem, and that 35,000 BOPD is the average incremental obtained from new wells by successfully removing and bypassing the drilling-induced damage. This paper discusses the production enhancement workflows, milestones, examples, results, lessons learned and strategies established to meet the production targets in various naturally fractured carbonate fields in Mexico.