Fishbone Well Completions to Enhance SAGD Operations

One of the biggest issues with SAGD is steam chamber growth in heterogenous reservoirs. Using this technology, the steam chamber is able to extend from multiple locations in the reservoir allowing for steam to travel through the reservoir easier. This allows for faster steam chamber growth and more sweep efficiency. Fishbones can also be used in place of infill wells, saving time in the future while producing oil from day 1.

Reducing the Steam-Oil Ratio (SOR) of thermal projects such as SAGD typically consist of new injection methods such as co-injection using polymers or solvents. What if we think bigger? What if we change the way we think about SAGD completions? With a change in bottom-hole configuration, not only can we adjust the shape and size of the steam chamber, but we could continue to add onto it. Fishbone completions in SAGD operations have only been attempted by one company in Alberta and the configurations were used only as infill wells. We wanted to see how the field could change with a new take on an already proficient design.

In order to determine how effective our designs were, we compared them to a base SAGD case run through the same reservoir and injection process, and along the same timeline of five years. Our design proved to produce about 20% more oil when compared over the first 5 years while reducing the SOR from 3.5 to 2.93. A detailed economic analysis was also performed showing significant improvement of the fishbone designs when compared to the base case. The design also allows for many optimizations to be made depending on the specifics of the reservoir.

In order to validate the fishbone, design the group simulated different fishbone architectures until the SOR decreased to under three using the program CMG Stars. The fishbones were simulated in a reservoir with the same heterogeneity as a typical McMurray reservoir. For the different fishbone architectures, the group started out with doing simulations with four flat (no elevation change) symmetrical fishbones (two on each side on the well) on just the producer or injector well, then had fishbones ramp up on those two cases. Finally, the team did the exact same simulations with the difference being that the four symmetrical fishbones were on both the injector and producer wells, with the fishbones being both flat and ramped up. Once these simulations were completed the team performed the exact same set of simulations but where the number of fishbones changed to six and eight fishbones. The final design that produced the lowest SOR of 2.93 was eight flat fishbones on both the producer and injector wells.

An important consideration when tackling this design project was the potential feasibility of this design in a real world SAGD operation. The reality of this technology is that practically all SAGD operations in Alberta are completed using standard vertical well configurations, or in some cases with a single parallel multilateral, however fishbone configurations have rarely been attempted here. However, fishbone style multilaterals have been used more commonly in other production markets around the world and have been proven to be effective in many cases. The technology to drill angled branches from the mother wellbore is readily available and the process for doing so is not brand new. The main barrier to the feasibility of the project is that drilling many fishbones could greatly increase initial capital cost, presenting higher financial risk for a project. With this in mind, the design was considered to be feasible to implement, with the understanding that the main barrier to implementation would be higher capital cost. An economic analysis of our designs was performed after simulation to gain further insight into the financial impacts of drilling fishbones compared to the gains of increased production.