Changing Economics of Unconventional Resource Plays
Charles H. Smith¹ and Lynda Ziane¹
Unconventional reservoirs have specific, difficult challenges related to their ability to produce hydrocarbons. These reservoirs have very low permeability and will not produce without extensive alteration by fracture treatment. Most completions use fracture treatment designs that are engineered to be placed at frequent intervals and with high proppant loads. These aggressive designs are used to provide maximum exposure of the surface area in the reservoir to the fracture treatment. This maximum exposure is supposed to achieve maximum flow rates. However, in our case study, treatments in some areas did not pump as desired. In other sections of the well, the reservoir accepted treatment, but production was dismal. Continued disappointment with these results demanded an attempt to define and alleviate the problem.
The first problem to be resolved was that even shale reservoirs must develop some amount of permeability to produce fluids to the wellbore. Thus, nuclear magnetic resonance (NMR) logs were acquired to get a direct estimate of permeability. These logs were run in a vertical pilot hole, and permeability was defined for each vertical section of the reservoir.
The next problem was to determine that the orientation of the well path was correct. This is critical because drilling in an impermeable section would result in poor fracture treatment placement and poor reservoir drainage. Therefore, dipole sonic logs were run in the pilot hole. Vertical and horizontal stress conditions were defined, and this information, along with permeability from NMR was used to develop the wellbore path and location. Dipole sonic logs were also run in the horizontal section to define the relative ability of the reservoir to accept treatment. Combining all of this data enabled an increase in the fracture treatment pumping efficiency in the horizontal completion sections from 40% to 100%. This application has been duplicated in other shale reservoirs with similarly positive results.
AAPG Datapages/Search and Discovery Article #90190©AAPG Southwest Section Annual Convention, Midland, Texas, May 11-14, 2014