The trajectory placement of a horizontal well that crosses a heterogeneous tight gas carbonate reservoir is one of the important elements that contribute to the success of well productivity. Proper placement can yield good production, and improper placement may lead to low well productivity. An effort was studied to improve the well productivity from an existing single horizontal well that was initially placed in suboptimal location by implementing the fishbone completion technology.
For this study, the simulation opportunity index (SOI) was selected as a method to indicate the remaining gas sweet spot in the reservoir. SOI integrates three independent components extracted from static and dynamic parameters: reservoir permeability thickness, movable gas, and reservoir pressure from a historically matched dynamic model. By using SOI, a map of the prospective gas sweet spots can be created; hence, low-performance existing wells are used to exploit the surrounding potential sweet spots using fishbone completion, which consists of tiny short needles with a maximum effective length of 32 ft placed along the horizontal section.
The study revealed that the fishbone completion in an existing low-production horizontal well can multiply the well productivity in a multilayer reservoir environment in addition to the significant production gain. Assisted history matching was used to explore the best combination of fishbone features, such as the number of subs required as the container room to hold the needles, optimal needle length, and optimal lateral drain section in which to place the subs and needles. Many sensitivities with the variables were run at once, and an analysis was conducted to identify the most-effective parameter to bring the highest well recovery.
Using the SOI method to scrutinize the best well candidates for fishbone completion and the required sub and needle placement not only helps rejuvenate the performance of the problematic well but also can aid in generating capital-expenditure savings and efficient project scheduling to manufacture fishbones with a proper number of subs and needles compared with blind fishbone technology installation.