Well stimulation is a highly technical and precise solution to decreased reservoir flow and production resulting from the accumulation of particles and fluids near the wellbore or formation damage resulting from the well drilling and completion process. Vital to the industry, well stimulation is a necessary intervention intended to enhance permeability and improve the flow of hydrocarbons from the reservoir to the wellbore. This significantly enhances productive well capacity, allowing a more timely return on investment.
The design of well stimulation procedures, however, quite often relies on large geologic and engineering datasets, which can be challenging to integrate and analyze. Thorough methods of data integration and visualization can help to maximize chances for success.
Two main classifications exist for well stimulation techniques and the use of one over the other is a function of the type of problem and the characteristics of the reservoir itself. These two classifications are chemical stimulation and hydraulic fracturing.
Chemical stimulation techniques are primarily used to address problems near or within a wellbore such as the blocking of perforations or the reduction of formation permeability by carbonate scale, migrating fines, fluid, or cement. These techniques have become increasingly selective and sophisticated since their introduction in the 1930s. Types of chemicals used, chemical concentrations, additives, application methods, corrosivity retarders, and safety considerations are just some of the factors that have been the focus of intense investigation and research.
In general, chemical stimulation techniques comprise the injection of chemicals, typically under pressure, into completed wells. Chemical constituents commonly include acids such as hydrochloric, hydrofluoric or acetic, water and potassium chloride brines, condensate (i.e. light-gravity oil), and designer mixtures targeted at specific hydrocarbon blocks. Gases, such as nitrogen and carbon dioxide, are also commonly injected along with the chemical constituents to assist in furthering the reach of the fluids into the reservoir. They also help with fluid removal once the desired chemical reactions are complete.
Unfortunately, since it’s often the case that problems chemical stimulation techniques are intended to rectify recur, adequate record keeping with regards to a well’s stimulation history is important. A well’s stimulation history can include a large volume of multi-disciplinary data and, as such, it is important to be able to integrate and visualize these datasets for complete analysis. Thorough analysis enables effective readjustment of follow-on stimulation procedures.
Hydraulic fracturing or “fracking” is an effective well stimulation technique that encompasses the opening up of fractures in a reservoir through the high-pressure injection of fracturing fluid. The fractures are then forced to remain open by proppant (i.e. small particles or grains such as silica, sand, or glass) which is injected into the reservoir with the fracturing fluid. Water and proppant are the primary components of fracturing fluid but chemical additives in small concentrations are commonly added to improve fracking performance.
Most productive formations can be stimulated by fracking with success hinging largely on one important parameter: formation permeability. Fracking is most suitable for low- to moderate-permeability reservoirs, although a reservoir with a permeability that is too low may be inadequate for economic production even with stimulation. Fracking is also effective in bypassing near wellbore damage in high-permeability reservoirs, as well as in other scenarios.
Another important consideration in assessing the potential for success in fracking is the location of confining shales. If the productive formation is confined between two massive shales, vertical extension of fractures can be limited. This scenario would also serve to concentrate the fracturing fluid and materials on the productive formation, supporting successful stimulation. As such, certain lithological sequences are more conducive to successful stimulation by fracking than others.
Fracking can be undertaken on a variety of scales from a small scour frac, intended to clear a small damaged area of the reservoir near the wellbore, to a large, multi-stage fracking operation intended to enhance permeability over a large volume of the reservoir. In multi-stage fracking operations, adjustments and improvements in procedure are continually being made as knowledge is gained with each event through the visualization and analysis of integrated datasets.
Leveraging Data Visualization and Analysis in Well Stimulation Design
The success of well stimulation methods, particularly those intended to treat large volumes of reservoir, is enhanced by data visualization and analysis. This is easily accomplished with the tools provided in the CoViz 4D software package. Candidate selection, treatment design, production forecasting, and economic analyses are keys to success. While wellbore problems can be treated with simple chemical stimulations requiring little data besides the nature of the obstructions themselves, the design of large stimulations can require volumes of both geologic and engineering data and this is due to heterogeneity inherent in reservoir characteristics.
Efficient and effective procedural design that minimizes the “pump and pray” approach relies on the integration of some or all of the following:
- core and rock sample data,
- mineralogical studies,
- geologic and petrophysical models,
- engineering rock properties,
- reservoir models,
- completion design information,
- seismic models,
- attribute studies and more.
CoViz 4D facilitates the integration of these data, which can then be used to give context to other sources of subsurface information, including microseismic data collected during fracking.
The success of well stimulation methods, particularly those intended to treat large volumes of reservoir, is enhanced by data visualization and analysis.
The successful integration of these often large data sets is necessary to maximize the potential for success and, thus, return on investment. Well stimulation can be a very complex undertaking made easier by the simultaneous visualization of both numerical and geospatial data, which would allow for facilitated analysis and decision making.