Estimating Proved Reserves in Tight/Shale Wells Using the Modified SEPD Method

Abstract

Abstract Due to their simplicity, empirical production forecasting methods have been used by the petroleum industry for decades. Since 2008, a number of empirical methods have been introduced to the petroleum industry, specifically for wells located in tight/shale reservoirs. However, most of these new methods are not reliable for forecasting remaining reserves, although they may appear to be very good for forecasting EUR in wells in which a high percentage of the EUR has already been produced. The Stretched Exponential Production Decline (SEPD) Method was introduced in 2010. Our results from analysis of both synthetic and actual field data by using SEPD have indicated that this method will most likely underestimate EUR in reservoirs with permeability ranging from 0.1mD to 0.0001mD. A modified SEPD (YM-SEPD) Method has therefore been developed to eliminate the SEPD Method's shortcoming by employing a new specialized plot to find all related parameters. This newly developed method is very easy to use and, most importantly, it will yield a much more reliable production and remaining reserve prediction for tight horizontal wells. With longer production histories, remaining reserves can be forecasted even more accurately and with a high confidence level. Hundreds of horizontal wells including oil wells from various formations (Cadomin, Montney, Notikewin, Cardium, Barnett Shale, Muskwa, etc.), hydraulically fractured in various ways, have been analyzed using the modified SEPD (YM-SEPD) method. Results indicate that reliable EURs and production profiles can be predicted readily for wells having only two to three years of production history. For wells having less than two years of production history, the modified SEPD (YM-SEPD) Method can also yield reasonable production forecasts when coupled with Duong's empirical method. This paper presents the application of the modified SEPD (YM-SEPD) Method to a number of actual and synthetic oil and gas wells to estimate their proved reserves, including horizontal wells producing dry, wet and retrograde gas as well as tight oil. These examples have had production histories with either observed or non-observed boundary-dominated flow (BDF). The examples also illustrate how the modified SEPD (YM-SEPD) method is capable of estimating proven reserves with high confidence.