Investigation of the Application of Horizontal Wells for Tight Gas Reservoirs
Engineering Honours Degree 2008
University of Adelaide
Tight gas exists in reservoirs with microdarcy‐range permeabilities and has huge future potential for global production. Australia and Oceania have approximately 34TCF in tight gas reserves, accounting for only 1.2% of the estimated global tight gas resources. These reservoirs commonly contain natural fractures, but generally cannot be produced economically without stimulation. Tight gas reservoirs have permeabilities less than 0.1mD. Reservoir engineers are presented with unique problems when applying material balance techniques to predict gas‐in‐place and reservoir performance.
This study examines the application of horizontal well technology for tight gas reservoirs
development. Horizontal wells are chosen in reservoir engineering applications to overcome or
circumvent technical, economical and environmental limitations that often plague vertical well
developments. Limitations encompass insufficient formation exposure, poor heterogeneity
knowledge and high pressure drawdown amongst others. The primary disadvantage of horizontal
drilling is the associated costs; currently 1.5‐2.5 times more than conventional vertical drilling.
Extensive literature reviews established that completion technology enables many levels of reservoir management efficiency. Some completion methods are basic while others are more complex in design. Completion design selection considers reservoir specific parameters and production constraints. Formation consolidation, reduced pore pressure, production rate and produced fluid properties all influence sand influx tendency. Sand production can be reduced by installing screen or gravel pack completions. Tight gas well deliverability can be improved by hydraulic fracturing and ‘frac‐packing’.
A well and reservoir performance investigation was completed using simulation software,
subsequent to a comprehensive literature review. Study results ascertained that well performance is influenced by reservoir and well parameters; permeability, pressure drawdown, drainage area,
lateral length, completion configuration and operating conditions. For instance, a reduced tubing head pressure results in higher gas production, whereas a reduced tubing size generates lower gas production. Tight gas reservoirs generally exhibit low productivity. This productivity however can be enhanced through hydraulic stimulation, given opportune economic incentive.
Horizontal drilling is considered feasible when kv/kh approaches unity. Permeability evaluation is
critical to ensure horizontal flow barriers will not impede production. Simulation demonstrates that
horizontal anisotropy has greater influence on reservoir performance than vertical anisotropy. A
maximum reservoir inflow was achieved when the well lateral was located centrally on the vertical
plane. Developing a reservoir with coning potential will likely warrant reassessment of well location
as coning influence were not simulated. Reservoirs producing high water‐ and condensate‐gas
volumes will operate at lower rates because of the higher gravity head. Furthermore, at high gas rates friction head can develop as fluid mixture properties change.
Tight gas reservoirs are estimated to have 2,800TCF of reserves globally. Future energy demands are likely to be supported through exploitation of this vast resource, particularly as technology advances and resources prove further economically beneficial. Ultimately, the implementation of appropriate completion technology would greatly benefit the development of Australia’s tight gas resources.