It goes without saying that the oil and gas industry faces unprecedented challenges today. Low oil prices are driving continued improvements in efficiency and a search for technologies to deliver barrels at the lowest possible cost. Health, safety, and environmental (HSE) impacts of chemicals used in drilling, completion, and production operations are under increased scrutiny from regulatory and community stakeholders. At the same time, more and more complex and technically challenging reservoirs must be developed to replace reserves.
Matrix stimulation is being used to maintain production from existing wells and reservoirs and maximize production from new wells at an attractive cost per incremental barrel. Close cooperation between suppliers, service companies, and operators is required to deliver systems-level life-cycle solutions that leverage the HSE benefit to improve effectiveness and operational efficiency.
Over nearly a century of application and study, acidizing technologies have been matured for relatively pure carbonates, clean sandstones (less than 10% carbonate), and temperatures below approximately 100°C. Today, the industry is developing reservoirs that have more-complex mineralogy, greater permeability contrast, and higher temperatures. New chemistries are being deployed to control the aggressiveness of stimulation fluids at high temperatures and to minimize the effect of unwanted damaging precipitation reactions. Sandstone matrix acidizing traditionally requires the use of a carefully designed sequence of stages to manage the complex reactions between hydrofluoric acid and siliceous minerals. New formulations that can be applied at higher temperatures and sometimes with a single stage have been developed and deployed in the field. In addition to increasing the potential application range and effectiveness, these formulations reduce the chemical footprint of sandstone stimulation. Laboratory data indicate that they are very effective but must be tailored carefully to the target reservoir. Continued experiments, theoretical modeling, and field testing are needed to understand and achieve the full benefits of deploying these new technologies.
In low-permeability carbonate reservoirs, acid stimulation is a low-cost alternative to propped hydraulic fracturing. New chemical and mechanical diversion technologies are being deployed to enable creation of distributed etched-fracture and wormhole networks along long interval and multilateral wells in low-permeability and heterogeneous reservoirs. These technologies are being taken up across the globe and are delivering optimized treatment designs and execution on a large scale.
Finally, there is an ongoing effort to use state-of-the-art simulation technologies (e.g., computational fluid dynamics) to model complex coupled reaction and flow processes and improve the understanding of stimulation processes and interpretation of more-detailed data now available (e.g., from distributed-temperature sensing).
Matrix stimulation remains a critical technology for delivering barrels at minimum cost. It is finding application in unconventional- as well as conventional-reservoir development. Chemical formulations and theoretical models continue to develop, sometimes incrementally and sometimes in step changes, to broaden the scope of application, improve effectiveness, reduce cost, and reduce HSE impact.
This Month's Technical Papers
CO2-Energized-Acid Treatment Reduces Freshwater Use, Boosts Well Performance
Sandstone-Acidizing System Eliminates Need for Preflush and Post-Flush Stages
No-Damage Stimulation By Use of Residual-Free Diverting Fluids
Recommended Additional Reading
SPE 173686 Optimization of Matrix Acidizing With Fluids Diversion in Real Time Using Distributed-Temperature Sensing and Coiled Tubing by Eber Medina, Pinnacle, et al.
SPE 179001 Field Results and Experimental Comparative Analysis of Sodium- and Nonsodium-Chelant-Based HF Acidizing Fluids for Sand-Control Operationsby Alyssa LaBlanc Smith, Halliburton, et al.
SPE 179017 An Improved Wormhole-Propagation Model With a Field Exampleby Xuehao Tan, Schlumberger, et al.
Lee Morgenthaler, SPE, is senior staff production chemist at Shell. He has been with Shell for 35 years, starting as a research chemist at the Bellaire Research Center. Morgenthaler has had assignments as a production engineer, research-and-development team leader, research manager, and production chemist on a wide variety of projects. These include technology development in completion and stimulation fluids, flow assurance, waterflooding, and field support for completion and stimulation activities in sandstone and carbonate reservoirs. He is currently working in Shell’s Upstream Americas Deepwater business, with roles in technology deployment and production-chemistry leadership. Morgenthaler holds a BS degree from Tufts University and a PhD degree from the University of Florida, both in chemistry. He is a member of the JPT Editorial Committee.
