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Abstract: Horizontal Drilling Potential in the Mid-Continent Region
Geological applications for horizontal drilling have proven most effective in tight fractured reservoirs, heterogeneous paleokarst reservoirs and porous and permeable reservoirs with coning problems. A modified version of standard fracture classification can be used to define most potential horizontal drilling targets in the Mid-Continent into four reservoir types.
The first type is characterized by little or no matrix porosity with the only porosity and permeability provided by fractures. The reservoir can be homogeneous or heterogeneous and may need to be overpressured to be an effective candidate for horizontal drilling. The Woodford Shale, the approximate equivalent of the Bakken Shale, may represent a good horizontal drilling target as does the Sycamore Limestone; both produce from fracture zones in Southern Oklahoma.
The Austin Chalk typifies the second type of HD-reservoir which has fair to good matrix porosity with low permeability. The only chalk reservoirs in the Mid-Continent region are in the northern and northwestern parts of the Denver Basin, as exemplified by the Upper Cretaceous Niobrara Formation.
The Viola and Mississippian limestones can be similar to the chalks in that they contain porous intervals with low permeability and they also can be self-sourcing. Both of these limestones are actively being pursued as horizontal drilling candidates.
The Arbuckle and Hunton groups contain reservoirs which are usually heterogeneous but have good porosity and fair permeability, which are often complemented by fractures. They represent the third type of HD-reservoir and are often characterized by a strong karst overprint. Paleokarst is a prevalent feature in Mid-Continent carbonates due to tectonic setting and unconformity relationships; it is often the cause of reservoir heterogeneity.
The fourth type may ultimately depict some of the most successful horizontal drilling applications; these are reservoirs with good porosity and permeability, usually homogeneous with coning problems, either gas or water. This fourth type of HD-reservoir may or may not be fractured; in fact, an abundance of fractures may actually increase coning problems.
Carbonates and shales are not the only horizontal drilling candidates in the Mid-Continent; sandstones and even granite wash, because of their depositional and diagenetic heterogeneity, are currently being examined and drilled using horizontal drilling methods.
Although horizontal drilling has yet to be proved a reliable method for increasing production efficiency in the Mid-Continent, there is an abundance of potential HD-reservoirs which provide targets for future horizontal drilling.
© 2016 South Texas Geological Society