Design of Multiple Transverse Fracture Horizontal Wells in Shale Gas Reservoirs

Abstract

Abstract The game changing technology enabling economic natural gas production from shale is the multiple fracture well (MFTW), a horizontal well with multiple transverse fractures. The well itself can create a stimulated reservoir volume (SRV) that delineates sufficient gas reserves to payout the well and provide continued return for several decades. This paper shows the importance of permeability and adsorbed gas in ensuring a well design that will achieve these objectives. In this paper we base decisions about the number and size of fractures and the horizontal well length (and therefore the fracture spacing) first on the physics of production and then on investment economics. Current practices using a repetitive well template applied to all wells in a given shale gas play result in some wells doing far better than expected while others barely pay out. We show that linear flow is likely to dominate production behavior until pressure interference occurs between adjacent fractures and that the time of inter-fracture interference predicted by linear flow pressure penetration is prolonged by desorption. The shale permeability and the adsorbed gas parameters are used to design an economically successful well while ensuring at least 50% gas recovery in the SRV within a specified period of time. Field data from several shale gas formations are used to provide examples of the well design approach. The gas adsorption characterization typically comes from laboratory analysis, which we use to develop what we have called the adsorption index. Because the gas recovery factor depends on lowering the average pressure in the SRV, permeability and the adsorption index are used to estimate the time of inter-fracture interference, which in turn indicates the optimal spacing between fractures. This paper provides insights on the effective exploitation of a shale gas reservoir by optimizing the fracture and well architecture.