The Cold Lake Oilsands deposits lie in Northern Alberta, near the border of Saskatchewan. The bitumen is located about 450 meters from the surface in the Clearwater sands and is overlain by the Colorado Shale and Grand Rapids formations. The Cold Lake area is home to many oil producers, including 2 major companies, one of whom operates the one of the largest in-situ thermal recovery operations in the world.

Cyclic Steam Stimulation (CSS) is the primary recovery method used in this area. Most well configurations within this area consist of 20-30 deviated production wells drilled from the central location (also referred to as well pad). CSS is a three-stage thermal recovery method consisting of a steam injection, soak, and production phase. Steam is injected into the reservoir at temperatures in excess of 300° C and pressures of 10-12 MPa.

The Cold Lake region is an environmentally sensitive area, and therefore well casing and caprock integrity are important factors to ensuring safe and sustainable operations.

Challenge

Well casings are subject to severe tensile stresses due to the high temperature, high pressure nature of the CSS process. These stresses have the potential to result in mechanical failures such as cement cracks or casing shear, which could lead to well downtime, damaging spills or hazardous blowouts. Shear stresses also develop in the overburden due to the dilation/uplift of the reservoir during the steam injection. Incursion of fluids into the overlying shales and aquifers above the caprock could occur, causing environmental contamination, resulting in large clean up costs and regulatory penalties.

Producers need to monitor their operations to demonstrate environmental due diligence and ensure their recovery operations do not damage the well casing or caprock. The clients also need to be made aware of potentially dangerous/damaging occurrences in the reservoir so that the appropriate response strategies can be enacted.

ESG’s real-time microseismic reservoir monitoring systems (ResMap™) have been instrumental in providing both clients with a viable cost effective means of demonstrating environmental and safety due diligence by monitoring well casing and caprock integrity.

ESG Solution

Since 2002 ESG has been responsible for the development and deployment of 2nd generation passive seismic monitoring systems and analytical techniques designed to detect the microseismicity associated with well casing failure and caprock breaches. These real-time reservoir monitoring systems have been deployed for multiple clients with operations in the Cold Lake Region, acting as an early warning system to potentially hazardous events.

Downhole multi-level (between 5-10) dual 3-component sensor arrays are cemented into monitoring wells located near the center of the CSS well pads. ESG’s 24-bit digital Paladin™ data acquisition units are placed at the well head to detect and record the microseismicity occurring around the well casing and caprock. The microseismic events are transmitted via DSL/Fiber optic cable to a centralized computer station where automatic processing begins.

ESG’s proprietary event classification software characterizes the microseismic events and looks for the specific signature of frequency characteristics of an event that could be caused by well casing shear. This classification scheme can detect potential failure occurrences and has been used to detect well casing shear and cement cracking based on the following criteria:

ESG’s ResMap™ system was assigned with an auto processing capability to automatically classify a casing failure event based on the following criteria:
More than 3 sensors detecting an event the P/S, Sh/Sv and R*PPV defined within certain thresholds.

In the event of a microseismic event meeting these criteria, ResMap™ enacts an early warning system, notifying the operators of the potentially dangerous events. ResMap™ can even be designed to provide automatic alerts through emails, cell phones or pagers.

Visualization software can also be used to construct a 3D map of the events to depict which ones are occurring close to the caprock. Figure 4 and 5 illustrates the waveforms associated with a casing failure event, as well as the location of casing failure events relative to well geometry.

 Outcome

ESG’s ResMap™ systems monitor CSS operations 24/7 for the life of the field operations and acts as an early warning system, giving operators the chance to react in real-time in the event a failure or breach occurs.

Clients within the Cold Lake Region have been able to demonstrate environmental due diligence and ensure their operations are complying with regulatory directives.
Producers have also been able to decrease well downtime, and develop response strategies to check wells which have experienced an heighted amount of microseismic activity. Depending on the event classification system and frequency of events, operators can prioritize which wells to check before undertaking another steam cycle.

One client used the information obtained from a monitoring system as the basis to adjust their steaming strategies. The client observed that many of the failures were occurring during the soak phase of the CSS process and were able make some adjustments to this phase and subsequently reduced the number of occurrences that took place.

References:
Smith RJ, Alinsangan NS, Talibi S, 2002 – Microseismic Response of Well Casing Failures at a Thermal Heavy Oil Operation, SPE/ISRM 78203