Identification of Production Potential in Unconventional Reservoirs

Abstract

fax 01-972-952-9435. AbstractUnconventional natural gas systems include fractured shale gas (FSG), tight gas sands (TGS), basin center gas (BCG), shallow basin methane (SBM), and coalbed methane (CBM). Recently, more operators are focusing attention on shale reservoirs. The most notable shale play being developed in the north Texas region is the Barnett shale. This success has encouraged operators to investigate producing potential of the Woodford and Caney shales in Oklahoma.Shale plays are unique in that they often are both the source rock and producing rock contained in the same package. This duality leads to difficulty in log and reservoir interpretation. To date, conventional log interpretation has proved inadequate in identifying producing potential. Simply perforating areas of high porosity and pumping massive hydraulic fracture (MHF) treatments do not always yield commercial production results. Identifying areas of high producing potential using gamma ray, density, resistivity, and sonic transit time to locate high total organic carbon (TOC) has also yielded mixed production results.We believe the addition of mechanical properties of the rock can help identify shale intervals with a high propensity to contain natural fractures and a high probability to create a fracture network during hydraulic fracturing. We propose a linkage between the mechanical properties of the rock and the hydraulic fracture network created during a MHF treatment and the resulting production outcome. Desirable combinations of mechanical properties are selected to help locate areas in the shale that have a propensity to fracture as a network with sufficient aerial extent to impact production results. We use these mechanical properties in addition to TOC and porosity to select fracture initiation sites and give a qualitative assessment of producing capacity. In this paper, we describe calculated log parameters that illustrate this technique.

Mineralogy-based brittleness prediction from surface seismic data: Application to the Barnett Shale

“…To estimate a reliable and robust reservoir brittleness measurement, it is necessary therefore to combine conventional well logs with direct measurements of geomechanical properties, such as Young's modulus E and Poisson's ratio ν (Grieser and Bray, 2007;Rickman et al, 2008). Figure 2.…”

“…The term brittleness average is proposed by Grieser and Bray (2007) as an empirical relationship between Poisson's ratio and Young's modulus to differentiate ductile from brittle regions. They hypothesize that ductile rocks exhibit a low Young's modulus and high Poisson's ratio, whereas brittle rocks exhibit a moderate to high Young's modulus and low Poisson's ratio.…”

“…They hypothesize that ductile rocks exhibit a low Young's modulus and high Poisson's ratio, whereas brittle rocks exhibit a moderate to high Young's modulus and low Poisson's ratio. Grieser and Bray (2007) normalize Young's modulus and Poisson's ratio by their ranges, resulting in scaled elastic parameters:…”

“…Jarvie et al's (2007) and Wang and Gale's (2009) brittleness index (BI) defines ductile and brittle regions in terms of its mineralogical content, generating a smooth transition between both regions. In contrast, Grieser and Bray (2007) define an empirical brittleness cut-off based on Poisson's ratio and Young's modulus. The cut-off depends on the shale play in which it is applied and on the expertise of the interpreter.…”

“…To do so, we need to reconcile and link conflicting brittleness parameters defined by Grieser and Bray (2007), Jarvie et al (2007), Rickman et al (2008), and Wang and Gale (2009).…”