The United States has had a significant oil and gas industry since Mr. Drake's oil well in Pennsylvania in 1859 attracted attention to the drilling of wells to produce oil. In the last decade, technology advances in both drilling and completion technology have had a significant impact on the ability to develop oil and gas reserves and have produced a new generation of wells for which extensive histories are not available at this time. A review of available historical data helps establish reasonable limits for decline trends of newer developments.
In order to better place limits on terminal decline rates for unconventional plays, data are presented showing terminal decline rates for a selected vertical developments and for selected horizontal developments in the United States. The curves reviewed include 292 type wells in 54 different producing horizons in the United States.
Some oil and gas developments have over 60 years of history and low decline rates. Others have high initial decline rates which do not flatten as expected for horizontal wells in low permeability reservoirs. The data for many of the developments also shows that decline trends beyond 10 to 20 years are frequently impacted by workovers and recompletions which have a significant impact on projected decline rates for a large number of long life wells.
Where both vertical and horizontal wells have been developed in an unconventional play, vertical well decline rates are generally less than horizontal well decline rates. The data also shows that gas decline rates are generally less than oil decline rates. When considered as a group, there is a band of decline rates which establishes reasonable upper and lower limits for newer developments using horizontal drilling and newer completion technology.