Depletion-induced Hazards and Risks and Their Management
By influencing the mechanical character of a field, production can result in one or some of the hazards shown below in red boxes. These hazards can lead to different socio-political, environmental, health and safety, and economic risks. Let’s take a very brief look at these hazards and their consequences:
Surface Facilities Damage
Uncontrolled surficial subsidence can damage or impact the serviceability of surface facilities such as storage tanks, pipelines and offshore platforms. If these hazards are not properly controlled, they can result in serious economic, safety and environmental risks. The iconic figure below shows the extensive sink of the legendary Ekofisk field in the North Sea driven by production (Photo: Norwegian Petroleum Museum).
Ground deformation induced by reservoir depletion has a direct influence on the integrity of producing or injection wells. Loss of the well integrity can pose different types of risks and, more especially, economic risks. Extreme ground deformations can even change the patterns of drilling new wells. The figure below shows an incident of casing damage recorded on an image built from ultrasonic wellbore televiewer in the Shengli Oilfield, China (Peng et al., 2005)
Significant depletion-induced deformation and stress change can result in fault reactivation and induced seismicity which, along with possible economic, environmental and safety risks, can influence the public perception of the subsurface operations. The extensive seismicity in the Lacq gas field in France shown below was believed to be caused by depletion (Bardainne et al., 2008).
Increase in sand production is another potential side effect of stress change induced by depletion. Sand production can influence the economics of the field. The figure below shows large amount of sand production in an oil field in Lake Maracaibo, Venezuela which experienced huge subsidence during production (Vasquez at al., 1999).
Significant mechanical changes induced by production can lead to degradation of sealing components, creation of new fractures, re-opening of existing fractures and faults and, consequently, compromising the hydraulic integrity of the reservoir. Any hydrocarbon leakage from the reservoir entails economic, environmental and socio-political risks.
The figure below shows heavy oil spill in Cold Lake, Canada (Pullman and Lokascss, 2013).
Reservoir compaction has paradoxical influences on production: while compaction is an important driving mechanism for production, it can also lead to reduction in the permeability of the reservoir and threaten the performance of the operations. The figure below shows how permeability decreases by changes in effective stress during production (Martin, 2018).
Integrated Subsidence Management Action Plan
To achieve an efficient field development and management plan, these hazards and risks should be studied under a comprehensive program that minimizes their adverse effects in a timely manner. A recommended risk management plan is shown below. Some details of this plan and its modules specifically ‘Risk Analysis and Assessment’, ‘Monitoring Planning’, and ‘Mitigation and Control Planning’ will be the subjects of future articles.