Very often, the average practitioner assumes that individual injection zones are isolated from each other - that there is no crossflow.

Recognizing the importance of contacting and mobilizing unswept in-situ oil, conformance in multi-layered scenarios becomes an essential consideration whenever the business objective is to maximize oil recovery. In this regard, the issue of crossflow must be considered in planning for any injection operations.

Crossflow is a term that means that different formations can communicate with each other. This can happen while you are injecting or when you shut down. It can happen because formations in contact with each other have "vertical" (in quotations because the formations do not have to be horizontal) permeability and there are different pressures in the formations. Flow will be from high pressure to low pressure and the result can be crossflow in the reservoir. Crossflow can also occur in the wellbore, where formations have different pressures. For example, when you shut down, fluid from a higher pressure formation can flow back into the wellbore and then, through the wellbore, flow into a lower pressured formation.

Many methods for predicting the oil recovery performance of waterfloods and produced water injectors assume that the layers in the reservoir are each continuous from well to well, uniform in properties and insulated from each other except at the wellbores. We generally visualize such a reservoir as a layer cake, with icing between each layer serving as the insulating material.

From what we know, few reservoirs satisfy the concept of shale streaks or impermeable beds acting as continuous material isolating each layer from each other. Some degree of crossflow will often exist away from the wellbore!

1. Assumptions Commonly Required or Made
2. Methods for Testing

1. Plan Ahead
• While the decision is ultimately economic, it is commonly much easier to mitigate than to remediate. Once nonuniform profiles develop, or excessive reservoir crossflow occurs, it may be difficult to overcome it effectively.
2. Be careful (and creative) on how you bring your injectors on line
• Methods are presented for minimizing the impact of nonuniform profiles by drilling, by completing in particular manners, by completing effectively, with isolation and by manipulating production. Don't forget to use the natural tendencies of formations to experience stress changes due to temperature and formation pressure changes. There are a number of documented cases where thermal stress manipulation during beanup has led to significant improvements in flow distribution that would not otherwise have been possible.

1. Recognize Why Intelligent Completions are Becoming More Important
• Fewer, larger well completions which complement advanced directional drilling capabilities
• Exploitation of multiple zones.
• Overall increasing sensitivity to unplanned OPEX, driving reliability (availability) requirements.
2. Primary Concepts
• Real-time surveillance is achieved with electronic devices and/or fiber optics.
• Real-time control is achieved by on/off control or choking. Real-time production/injection control has been commercially available only since about 1998. Control is achieved by electric, hydraulic or electro-hydraulic actuation of a valve or sleeve.
• The first implementation of intelligence in completions began in the late 1980s, with the installation of pressure-temperature gauges to give real-time readings of well bottomhole pressure. Prior to development of interventionless technology in the late 1990s, zone flow could only be modified with rig intervention or by coiled-tubing-conveyed methods of perforating, squeezing, or shifting a sleeve.