Analysis of Production Data with Elliptical Flow Regime in Tight Gas Reservoirs

Abstract

Analysis of production data for tight gas reservoirs is based on pressure transient (PT) analysis, which is now a conventional procedure for fractured tight gas reservoirs. Key parameters can be estimated during the analysis: fracture conductivity, fracture half-length and reservoir properties. Most PT analysis methods deal with bilinear, formation linear, and pseudo-radial flow regimes. It is well known that an elliptical flow regime can appear between formation linear and pseudo-linear flow regimes. Sometimes the period is very short and cannot be identified. But there are many cases when only formation linear and elliptical flow regimes are present in production data records and the time needed to reach the pseudo-radial period is more than decades. Most PT analysis methods substitute elliptical flow regime for pseudo-radial, which may lead to the incorrect calculation of key parameters of reservoirs and fractured wells. In this study, we present the development of an approach for elliptical regime analysis in the production data record for calculation of key parameters of finite-conductivity fractured wells and reservoirs: fracture conductivity, fracture half-length, reservoir permeability, and effective drainage area. This method uses an analytical equation for elliptical flow period and estimation of parameters from the equation. The development is based on more stable deconvolution analysis of production data with variable rate/pressure and more reliable analysis of response function after deconvolution. We present here some synthetic and field cases to demonstrate the results of calculations. Introduction Classic well testing approaches for fractured wells involving pseudo-radial flow models cannot be applied since the pseudo-radial regime is reached in decades or years of production in tight gas reservoirs. In many cases, we cannot observe pseudo-radial flow. Really, we deal with elliptical flow after the formation linear period. To receive more realistic results of production data analysis, the best solution is to use elliptical flow model for early- and mid-time production periods (which could actually last for years). Under this assumption we are able to extract approximate permeability and fracture half-length and conductivity values. At the moment, there is literature (Cheng et al. 2007; Hale and Evers 1981; Amini et al. 2007) that presents methods of work with elliptical data. It is reasonable for commercial tools to have robust algorithms for work with production data where elliptical flow regime is exhibited. Integration of the algorithms in production modeling workflow will allow more reliable results of production data analysis. Reservoir characterization and well completion efficiency evaluation involve a multilayer commingled reservoir using commingled system well production performance data. Commingled well production data from a system with a number of different layers with varying reservoir and well completion properties generally should not be evaluated using an equivalent single layer reservoir analog. The results of the analysis for determining estimates of the reservoir properties and completion efficiencies of each of the individual reservoir layers will be very inaccurate in this case. Splitting production data for each layer is an important step for correct analysis. Helpful information on splitting can be found in (Poe et al. 2006).

Well test, rate transient analysis and reservoir simulation for characterizing multi-fractured unconventional oil and gas reservoirs

“…Depending on the well completion type and the reservoir geological and geometric attributes, different flow regime might be revealed on pressure transient diagnostic plots. In conventional well test analysis, diagnosis of the radial flow regime is critical in quantitative well test interpretation, since a reliable value for reservoir permeability can be estimated when the late-time radial flow regime is established in the reservoir (Badazhkov 2008;Bourdarot 1998).…”

“…Due to the insufficient permeability of the shale reservoirs, they require efficient stimulation using hydraulic fractures to produce hydrocarbon in commercial quantities (Bagherian et al 2010).…”

Interpretation of Reservoir Flow Regimes and Analysis of Welltest Data in Hydraulically Fractured Unconventional Oil and Gas Reservoirs

“…Depending on well completion type, completion configuration, reservoir geological and geometric attributes, different flow regime might be revealed on pressure transient data (Bourdarot, 1998). Based on derivations of fluid flow and diffusivity equations, on the pressure transient derivative curve, the slope of +1 shows wellbore storage effect, the slopes of -0.5 (-1/2), +0.5 (+1/2), +0.25 (+1/4) and +0.36 (approximately +1/3) indicate spherical, linear, bi-linear and elliptical flow regimes respectively, and zero slope indicates radial flow regime (Badazhkov, 2008;Bourdarot 1998). When radial flow regime is established in the reservoir, reliable values for permeability and skin factor can be calculated for the formation layers that contributed to the test.…”

“…When radial flow regime is established in the reservoir, reliable values for permeability and skin factor can be calculated for the formation layers that contributed to the test. Therefore, diagnosing the radial-flow regime is critical to quantitative welltest interpretation (Badazhkov, 2008). Figure 5a.…”

An Improved Rate-Transient Analysis Model of Multi-Fractured Horizontal Wells with Non-Uniform Hydraulic Fracture Properties

“…Some works investigated rate decline analysis for the wells with long period of linear flow (mainly for the vertically fractured well) [34,35]. Badazhkov et al presented a method for elliptical regime analysis since it is hard to reach pseudo-radial flow in tight reservoirs [36]. The empirical methods have been developed to address the limitations of the Arps curves.…”