Qualitative well placement and drainage volume calculations based on diffusive time of flight Seyyed Abolfazl Hosseini a, ⁎, Suksang Kang b , Akhil Datta-Gupta b a Bureau of Economic Geology, Jackson School of Geological Sciences, University of Texas at Austin, TX, United States b Texas A&M University, TX, United States abstract article info Article history: Received 28 June 2010 Accepted 9 November 2010 Available online 19 November 2010 Keywords: diffusive time of flight drainage volume well placement streamline Streamlines have been very effectively used for computing swept volumes and drainage volumes in oil reservoirs. However, there is an incorrect but commonly held perception that streamlines cannot be used for gas reservoirs. In fact, streamlines exist whenever there is an underlying velocity field—both in compressible and incompressible flow. In this paper we present one of the first applications of streamlines to tight gas reservoirs for drainage volume calculations of producing wells, optimal placement of infill wells. Current practice of well placement in tight gas reservoirs generally involves the use of empirical correlations based on reservoir properties and past production histories and/or pressure maps from flow simulation. No rigorous procedure is available to compute well drainage volumes in the presence of heterogeneity and hydraulic fractures, particularly for complex wells. We propose a fast approach for drainage volume calculations based on the streamlines and diffusive time of flight and demonstrate its application to optimize well placement. Our approach relies on a high frequency asymptotic solution of the diffusivity equation and emulates the propagation of a ‘pressure front’ in the reservoir. This allows us not only to rigorously compute the well drainage volumes as a function of time, but also to examine the potential impact of infill wells on the drainage volumes of existing producers. Using these results, we present a systematic approach to optimize well placement to maximize the estimated ultimate recoveries (EUR). We demonstrate the power and utility of our method using both synthetic and field applications. The synthetic example is used to validate our approach by establishing the consistency between the drainage volume calculations from streamlines and the EUR. The field example is from the Wamsutter gas field, one of the largest gas fields in the Rocky Mountain region. We utilize the streamline-based drainage volumes to identify depleted sands and generate a reservoir quality map to optimize future well placement based on the undepleted regions. Field application clearly demonstrates a systematic and efficient approach to optimal well placement in tight gas reservoirs. Published by Elsevier B.V. 1. Introduction Estimation of the reservoir size and drainage volumes of individual wells is a very important key in the management and development of oil and gas fields. These properties are directly related to economic problems like planning a new infill well in a producing field and adjusting well schedules to maximize production. For accurate production estimation, various approaches have been proposed and applied to synthetic and field cases. Earlier works of Anderson (1991) proposed a reservoir volume calculation technique based on the pressure profile of a field and mapping over the reservoir. The authors drew a pressure contour to provide a simple analytical scheme that yielded a basic understanding of drainage area and suggested its usefulness on infill drilling, well abandonment, and water injection. But this approach required too many assumptions such as being limited to horizontal, homogeneous, isotropic, two-dimensional reservoirs and so on. Kulkarni et al. (2001) suggested the generalized streamline approach to mimic transient pressure function by introducing a diffusive time of flight. They showed that diffusive time of flight can be used to define the drainage radius in case of primary recovery or compressible flow under homogeneous and heterogeneous conditions. Zhong et al. (2004) tried to match the arrival time of a transient pressure front and the decline-type curve that was derived from pseudo-steady state flow condition. They mainly focused on reconciling the drainage volume calculations from decline curve analysis and streamline models. They concluded that their proposed approach can be used for inferring the flow barriers and reservoir compartmentalization, which are used for drainage volume estimation. Paulo et al. (2004) used the ‘quality map’ to estimate the production potential of a reservoir. They showed a good correlation between the average value of the uncertainty quality map and the Journal of Petroleum Science and Engineering 75 (2010) 178–188 ⁎ Corresponding author. Tel.: +1 512 4712360. E-mail address: seyyed.hosseini@beg.utexas.edu (S.A. Hosseini). 0920-4105/$ – see front matter. Published by Elsevier B.V. doi:10.1016/j.petrol.2010.11.012 Contents lists available at ScienceDirect Journal of Petroleum Science and Engineering journal homepage: www.elsevier.com/locate/petrol