Productivity and Drainage Area of Fractured Horizontal Wells in Tight Gas Reservoirs

Abstract

Summary This paper discusses the performance and productivity of fractured horizontal wells in heterogeneous, tight-gas formations. Production characteristics and flow regimes of unfractured and fractured horizontal wells are documented. The results show that if hydraulic fracturing affects stress distribution to create or rejuvenate natural fractures around the well, the productivity of the system is significantly increased. Unless there is significant contrast between the conductivities of the hydraulic and natural fractures, hydraulic fractures may not significantly contribute to the productivity. For extremely tight formations, the effective drainage area may be limited to the naturally fractured region around the well and the hydraulic fractures. It is also shown that very long transient flow periods govern the productivity and economics of fractured horizontal wells in tight formations. The results of this study are also applicable to oil production from fractured shale. Introduction Economic gas and oil production from low permeability reservoirs has been a challenge for the oil and gas industry. Because most of the high permeability reservoirs have been exploited and many low permeability reservoirs remain undeveloped, the latter have taken the industry attention recently. Particular attention has been given to tight-gas reservoirs with permeability in the range of micro-Darcies or below and to oil accumulation in fractured shale. Hydraulically fractured horizontal wells are the proven technology to produce oil and gas from tight formations. Hydraulic fractures reduce well drawndown, increase the productivity of horizontal wells by increasing the surface area in contact with formation, and provide high conductivity paths to the wellbore. Depending on in-situ stress orientation, hydraulic fractures can be parallel (longitudinal) or perpendicular (transverse) to horizontal well axis. Project economics in tight formations, however, depends strongly on well spacing and the number of hydraulic fractures required to drain the reservoir efficiently. Field evidence indicates that the drainage areas of fractured horizontal wells in tight formations may be limited to a rectangular region confining the horizontal well and the transverse hydraulic fractures. Also, there has been evidence that hydraulic fracturing in tight formations changes stresses in fracture drainage area, which could create or rejuvenate natural fractures in the near-vicinity of the horizontal well. This fracture network, which may be characterized as a dual-porosity system, may contribute significantly to improve productivity of the fractured horizontal well. Much work has been done (Soliman et al. 1990; Larsen and Hegre 1994; Temeng and Horne 1995; Raghavan et al. 1997; Wan and Aziz 1999; Al-Kobaisi et al. 2006) to investigate pressure-transient analysis and short- and long-term productivity of horizontal wells with single or multiple hydraulic fractures. The effect of a dual-porosity zone surrounding hydraulic fractures, however, has not been considered in the previous studies. The main objective of this study is to investigate the combined effects of a dual-porosity region and hydraulic fractures on the productivity of horizontal wells. The results presented in this work are based on a semianalytical model developed by Medeiros et al. (2006). The model was derived from the Green's function formulation of the solution for the diffusivity equation (Gringarten and Ramey, 1974, Ozkan and Raghavan, 1991a, 1991b) and has the capability to incorporate local heterogeneities. In this work, we use the semianalytical model to incorporate induced finite-conductivity fractures (transverse and longitudinal) along the horizontal well and naturally fractured zones around the hydraulically fractured horizontal well by using the dual-porosity idealization. We use the example data sets given in Tables 1 through 3 to consider different cases of horizontal wells with and without induced and natural fractures.

Production Analysis of Multi-Stage Hydraulically Fractured Horizontal Wells in Tight Gas Reservoirs

“…Lewis and Hughes (2008) presented type-curves for single and dual-porosity gas reservoirs using a modified material balance time. Medeiros et al (2008) presented a semi-analytical solution for the MFHW. Jordan et al (2009) presented a trial and error method to match production data and estimate original gas in place and other parameters using semi-analytic quadratic rate-cumulative production related.…”

Analysis of Production Data From Hydraulically Fractured Horizontal Wells in Shale Reservoirs

“…Productivity might be improved further if the horizontal well and hydraulic fractures are connected to an active natural-fracture network. This fracture network may be preexisting in a naturally fractured reservoir (dual-porosity system) or may be generated or reactivated locally by hydraulic fracturing around the well (Fisher et al 2004;Mayerhofer et al 2005;Maxwell et al 2006;Medeiros et al 2008).…”

“…For extremely tight formations, the existence of an invasive network of fractures (natural and induced) around the well provides the effective conductivity required for commercial production of hydrocarbons (Mayerhofer et al 2005;Medeiros et al 2008). In unconventional reservoirs with matrix permeabilities at the nanodarcy range, such as shale, the near-well region with invasive fractures is referred to as the stimulated reservoir volume (SRV) and constitutes the effective drainage volume of the well (Fisher et al 2004;Mayerhofer et al 2005;Maxwell et al 2006;Medeiros et al 2008).…”

Research on the production performance of multistage fractured horizontal well in shale gas reservoir

“…Based on the viewpoint that the productive life of fractured wells in tight reservoirs is always dominated by the linear flow period (Medeiros et al, 2008), Brown et al (2009) noted that the key characteristics of flow convergence toward a multi-fractured horizontal well may be presented in a relatively simple model. Thus, this paper presents an effective unsteady productivity model of shale gas through a one-dimensional linear flow model.…”