As an industry, we have a vital need to invest in our aging reservoir base. At the same time, exploration and development costs are increasing, and we face persistent pressure to contain and reduce capital and operating expense wherever we can. Furthermore, the value of bypassed hydrocarbons in the reservoir at today's prices is greater than ever. Draining reservoirs for maximum recovery and aligning our efforts with appropriate capital investment is imperative, and this focus must begin from the outset of field development. The key to achieving this objective is reservoir monitoring.
In the past 10 years, the focus of reservoir monitoring has evolved from events in individual well bores to those in the field as a whole, reflecting a number of significant technology developments. Schlumberger has become the first company with a full technology offering in this sphere, including electromagnetic imaging (EMI), borehole and 4-D (time-lapse) seismic, and real-time production monitoring.
The new technology of EMI is now proving an effective tool in crosswell analysis, complementing the information obtained through borehole seismic. Deep electromagnetic imaging allows wireline evaluations at the reservoir level versus only a few feet from the well bore. This makes EMI useful for locating bypassed pay, time-lapse imaging of water and steam floods, establishing well correlations, and mapping interwell structure. Mapping of interwell electrical resistivity is possible through numerically inverting crosswell EMI data.
The combination of controlled-source EMI surveys with surface or borehole seismic offers considerable potential to develop field-scale fluid monitoring to even greater levels. Already we can combine deep electromagnetic measurements with well log data to create 3-D images of saturation across the reservoir. A remaining challenge is to achieve full integration of EMI and crosswell borehole seismic, which will pay strong dividends, particularly in brownfield development. EMI will also soon be part of the reservoir management workflow, as borehole seismic already is.
Other major technologies that have moved the industry beyond episodic single-well evaluation into full field evaluation include real-time multiwell production monitoring and 4-D seismic.
Through reservoir monitoring services, including worldwide connectivity to enable remote real-time decision-making, it is now possible to act immediately on what is seen via monitoring - not only to optimize a well but the field as a whole.
This system is designed to identify problems with well performance and well operating conditions. Specific real-time data are processed with contextual data to describe the state of the production operating system. Surveillance reports display alerts that can be triggered by threshold, time-based variance and model-based variance criteria. Through the integration of information into the reservoir management process, periodic reservoir assessments can be made and key field development decisions implemented.
The use of 4-D seismic monitoring provides a field-wide view enabling identification of water encroachment, remaining volumes of bypassed hydrocarbons and other changes as the reservoir reacts to the production process.
Nonetheless, 4-D seismic - as well as real-time production monitoring - has to deliver usable data quickly enough to fit into current engineering workflows to be of much value. Thus, time-lapse seismic results must easily loop back into the dynamic reservoir model.
While reservoir monitoring is not yet where we want it to be, the ongoing developments in real-time production monitoring, EMI and seismic integration workflows, and 4-D seismic applications are bringing us closer and closer.

Jeff Spath is president of Schlumberger Data & Consulting Services.

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