Paper 5991: How Much Gas, Condensate, and Oil Will be Produced from Major Shale Plays in the U.S., and Why?

Monday, 15 December 2014: 4:00 PM
Tadeusz W Patzek, UT Austin, Austin, TX, United States
A one-dimensional universal model of gas inflow into the hydrofractured horizontal wells (Patzek, et al., PNAS, 110, 2013) was developed for the Barnett shale, and applied to explain historical production and predict future production in 8294 wells there. Subsequently, this model was extended and applied to 3756 wells in the Fayetteville shale, 2199 wells in the Haynesville shale, and 2764 wells in the Marcellus shale. Out of these, 2057, 703, 1515, and 1063 wells in the Barnett, Fayetteville, Haynesville, and Marcellus, respectively, show evidence of pressure interference between consecutive hydrofractures. For the interfering wells, we calculate their EURs and the distributions of effective gas permeability in the reservoir volumes influenced by these wells. For the non-interfering wells we calculate the lower and upper bounds on their EURs. We show that given the available data, a better field-wide prediction of EUR is impossible. The expected EURs vary between 0.4 and 4.3 Bscf in the Barnett, depending on the well quality. In the other shales the expected well EURs are 0.5 – 3.4 Bcf in the Fayetteville, 1.4 – 7.9 Bcf in the Haynesville, and 1 - 9 Bcf in the Marcellus. The respective mean effective gas permeabilities are 400, 1000, 230, and 800 nanodarcy for the same shales, much high than the core values. Work on the Eagle Ford shale is in progress and will be presented in December.

In a shale- horizontal well system, we model rectilinear flow of natural gas as dimensionless nonlinear pseudo-pressure diffusion IVBP with gas sorption on the rock and the multiple planar hydrofractures acting as internal sorbing boundaries. After the initial choked flow, wells must decline as the inverse of the square root of time on production, until the gas pressure starts declining at the midplane of a reservoir cell between two consecutive hydrofractures. At this point of time production decline is exponential. The transition between the square-root-of-time and exponential decline is governed by the characteristic pressure diffusion time, τ, and gas mass in place, M. The dimensionless solution of this IVBP problem reduces the cumulative gas production in all wells to a single universal curve for each play. The ultimate recovery is about 15% of gas-in-place and less so for oil.