What Factors Control Shale-Gas Production and Production-Decline Trend in Fractured Systems: A Comprehensive Analysis and Investigation

Abstract

SummaryOne of the biggest practical problems with the optimization of shale gas stimulation design is estimating post-fracture production rate, production decline, and ultimate recovery. Without a realistic prediction of the production decline trend resulting from a given completion and reservoir properties, it is impossible to evaluate the economic viability of producing natural gas from shale plays.Traditionally, decline curve analysis (DCA) is commonly used to predict gas production and its decline trend to determine the estimated ultimate recovery (EUR), but its analysis cannot be used to analyze what factors influence the production decline trend due to lack of underlying support of physics, which make it difficult to guide completion designs or optimize field development.In this article, we presented a unified shale gas reservoir model, which incorporates real gas transport, nano-flow mechanisms and geomechanics into fractured shale system. This model is used to predict shale gas production under different reservoir scenarios and investigate what factors control its decline trend. The results and analysis presented in the article provide us a better understanding of gas production and decline mechanisms in a shale gas well with certain conditions of the reservoir characteristics. More in-depth knowledge regarding the effects of factors controlling the behavior of the gas production can help us develop more reliable models to forecast shale gas decline trend and ultimate recovery. This article also reveals that some commonly hold beliefs may sound reasonable to infer production decline trend, but may not be true in a coupled reservoir system in reality. IntroductionWith ever increasing demanding for cleaner energy, unconventional gas reservoirs are expected to play a vital role in satisfying the global needs for gas in the future. The major component of unconventional gas reservoirs comprises of shale gas. Shales and silts are the most abundant sedimentary rocks in the earth's crust and it is evident from the recent year's activities in shale gas plays that in the future shale gas will constitute the largest component in gas production globally, as conventional reservoirs continue declines (Energy Information Administration 2015). According to GSGI, there are more than 688 shales worldwide in 142 basins and 48 major shale basins are located in 32 countries (Newell 2011). Better reservoir knowledge and advancing horizontal drilling and hydraulic fracturing technologies make the production of shale gas resources economically viable and more efficient.

Analysis of the Influencing Factors on the Well Performance in Shale Gas Reservoir

“…At the end of the first stage, the production rate of the adsorbed gas approaches to the maximum at the rate of 6.5 × 10 3 m 3 . Our finding is consistent with Wang [25] who states that the existence of adsorption gas has a more obvious effect on the production decline in the early stage and this is contrary to the common belief that the adsorption gas becomes important only when the average pressure in the reservoir drops to a certain level. In the second stage, the production rate starts declining.…”

Hydraulic fracture propagation in naturally fractured reservoirs: Complex fracture or fracture networks

“…These shear failures of natural fractures discharge acoustic energy across the reservoir and can be detected via microseismic monitoring during stimulation. If these stimulated natural fractures are not well connected to the main hydraulic fracture, they have little contrition to production enhancement (Wang 2017). This also reflected in field observation that microseismic events do not correlate to production at all (Moos et al 2011).…”

Towards Quantifying the Likelihood of Water Resource Impacts from Unconventional Gas Development

“…This mechanism is more often associated with CBM due to the shallower depths at which the gas is found rather than in shale gas and tight gas formations (i.e., there is more likely to be a connection between coal measures and overlying aquifers). Pressure drops are common and necessary for the production of both shale gas and CBM (Moore 2012;Mahdi et al 2017;Wang 2017), although the timing and extent of the pressure changes in the formation do differ between these types of formations. For shale production, this pressure drop is related to the production of gas, whereas for CBM the pressure drop results from the removal of (typically) large volumes of water.…”