Worldwide, it is estimated that an average of three barrels of water are produced for each barrel of oil1. The total cost of separation, treatment and disposal of water has been estimated to be about $50 billion/year2 in the oil industry. This is because water is commonly co-produced with the hydrocarbons saturating the reservoir rock. Excessive water production is prevalent in mature fields globally where the ratio of water to oil produced increases to nine. This can have an impact on the profitability of oil and gas assets in mature fields.
Therefore, it is important to fully understand the different mechanisms that contribute to undesired water production to better evaluate existing information, identify additional tests, and design the optimum solution to the problem. A large number of chemical and mechanical “conformance / water control technologies” are available to mitigate water-related issues. These technologies not only shutoff or slow down water production, they also significantly increase hydrocarbon production rates and extend the life of the reservoir.
Mechanisms of Unwanted Water Production
Table 1 summarizes the most common water production issues. These scenarios have been extensively discussed in the literature. In order to achieve high levels of treatment success, the nature of the problem must be identified correctly. Each problem usually requires a different approach when trying to find the most optimum solution.
Table 1. Conformance Problems and Applications
| Near-Wellbore Problems | Reservoir-Related Problems |
| Casing leaks | Coning or cresting |
| Temporary chemical isolation | Fractures, fissures or voids |
| Lost circulation while drilling | Channel from injector |
| Lost circulation while workover | High permeability streak |
| Channeling behind casing | Completion near a water zone |
| Water shutoff for gravel pack | Fracturing job went to water |
| Plug-back | Watered-out zone |
| Shutting-off perforations | Acidizing near water zone |
How to Identify Conformance Problems
Production trends provide a good indication of the type of water-related problem. For example, a steep increase in the water cut may indicate that a casing leak or channeling behind casing has occurred (Figure 1). On the other hand, a slow water cut upturn may suggest that water has slowly encroached from a water zone below. Diagnostic plots3 (water-oil-ratio (WOR), WOR-derivative vs. time) can be also used to aid in this regard.
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Figure 1. Conformance problems associated with water cut trends
If the reservoir is under waterflooding, higher WOR in certain wells compared to others in the same area can be a good indicator of water channeling from injector to producer wells. In other cases, when robust geological and simulation models of a large reservoir are available, water production problems can be analyzed and diagnosed by the oilfield operator.
Well logs are often referenced to identify water production problems. Table 2 shows logs mainly used to identify water issues. Open-hole logs are the most widely available source of information for initial water-oil-contact (WOC), fluid saturation, and permeability of the reservoir.
Table 2. Main Applications of Logging Tools to Diagnose Conformance Problems
| Problems | Open-Hole Logs | Cement Evaluation Logs |
Casing Evaluation Logs | Pulsed Neutron Logs |
Production Logs |
| Lost circulation while drilling | X | ||||
| Lost circulation while workover | X | ||||
| Coning or cresting | X | X | |||
| Casing leaks | X | X | X | ||
| High perm streak | X | X | |||
| Completion near water zone | X | X | X | ||
| Fracturing job to water | X | X | X | ||
| Channeling behind casing | X | X | X | X | |
| Channel from injector | X | X | |||
| Watered-out zone | X | X |
A cement bond log (CBL) is the primary tool to evaluate the quality of cement and diagnose the location of cement failure to pinpoint where the repair is needed. After a well is put on production, production logging is one of the most commonly used tool that can reveal information on the type of fluid and flow rate using spinner, temperature, and pressure data. An array of cased-hole logging tools, such as Halliburton’s RMT EliteTM Reservoir Monitor Tool and Pulsed Spectral Gamma (PSGSM) Logging Service, provide a more in-depth assessment of hydrocarbon and water saturation behind casing. This information can indicate the source of water production as well as potential zones for further analysis development.
There is not a unique way to diagnose all excess-water problems. Halliburton’s experts provide a comprehensive approach to successful identification and mitigation of water production issues.
References
1 Bailey, B et al “Water Control” Oilfield review (2000) 12, No. 1, 30.
2 Water Management-An Increasing Trend in the Oil and Gas Industry. Freeman Hill, Steve Monroe, and Reshmy Mohanan. SPE/EAGE European Unconventional Resources Conference and Exhibition, 20-22 March 2012, Vienna, Austria
3 Chan, K. S. Water Control Diagnostic Plots. SPE Annual Technical Conference and Exhibition, 22-25 October 1995, Dallas, Texas
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