Matrix stimulation encompasses pumping processes used to improve the connection between the wellbore and the reservoir. They are effective in a wide range of lithologies and have been successful in most types of completions: cased and openhole, horizontal and vertical, simple and complex, injectors and producers. Wells are matrix stimulated during completion and to remove production- or injection-induced impairment. The defining characteristic of matrix stimulation is the use of chemical systems to dissolve material in the near-wellbore region pumped at pressures below those that propagate reservoir fractures.
Chemical systems have been developed to attack carbonates (impairment and reservoir material), organic deposits, aluminosilicate minerals (fines), and sulfate scales. They have been used widely below approximately 120°C, but formulating effective systems for higher temperatures is a challenge. Carbonate dissolution is generally extremely rapid at downhole conditions. Current developments are focused on controlling this reaction either with novel organic acids or with gel systems whose rheology changes with the acid reaction. Solvents for organic deposits and sulfate scales react very slowly. The challenge is to speed up the reaction and develop treatment methods with the necessary contact time. The reaction with fines is extremely complex and can lead to precipitation of solids that are more damaging than the minerals themselves. Several promising new chemistries combining chelants and organic acids are being studied to prevent these damaging precipitates.
Matrix-stimulation treatment design is based on experience-based guidelines, simple chemical-reaction-model calculations, or sophisticated models that combine reaction modeling and fluid-mechanical calculations to optimize chemistry, select volumes, and define rates and pressures. More-sophisticated models are used for critical wells and expensive treatments. Model refinements are being published continually, applying new software capabilities or new methods to manage uncertainties in the input data for deterministic models to improve outcomes. One of those is summarized in this issue.
Matrix stimulation has benefited from developments in other technologies. Distributed-temperature sensing and smart-well devices are deployed to measure and manage acid placement. Novel perforation technologies are coupled with chemical stimulation to improve connection with the reservoir. The potential benefit of chemical stimulation to remove impairment in shale gas and oil reservoirs is just starting to be understood. Recent case studies describe an integrated approach to optimizing chemical systems and applying novel design and execution technologies to improve outcomes. Two of these are presented here.
This Month's Technical Papers
Recommended Additional Reading
SPE 165084 Acidizing Sandstone Formations Using a Sandstone Acid System for High Temperatures by L. Zhou, Texas A&M University, et al.
SPE 165100 Computational Fluid Dynamics as a Tool for Pumping-Strategy Evolution on Matrix-Acidizing Treatments by Andressa R. de Melo, ESSS, et al.
SPE 166224 Optimum Changed Perforation and Stimulation Treatment for Improving Zonal Productivity: Key Enablers for Strategic Reservoir Management of Deep High-Pressure/High-Temperature Sour Carbonates in North Kuwait by San P. Pradhan, Kuwait Oil Company, et al.
|Lee Morgenthaler, SPE, is senior staff production chemist at Shell. He has been employed by Shell for 33 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.|
Lee Morgenthaler, SPE, Senior Staff Production Chemist, Shell
01 June 2014
New Closed Blender Reduces Footprint, Gasification of CO2 in Waterless Fracturing
Carbon dioxide (CO2) waterless fracturing uses liquid CO2 to replace water as the fracturing fluid in reservoir stimulation. The continuity and reliability of the blender are key factors determining performance of the operation.
New Acidizing Method Improves Stimulation in Deep, High-Temperature Offshore Well
The complete paper discusses a method of stimulating deep, high-temperature offshore wells by combining an efficient single-phase retarded acid (SPRA) system and an engineered, degradable, large-sized particulate and fiber-laden diverter (LPFD).
Several well-stimulation products and techniques have been seen to benefit well productivity from recent field trials and implementations in carbonate reservoirs, including simpler acid fluid systems, integrated work flows, and coiled-tubing bottomhole assemblies.
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