Abstract

The phenomenological theories of gas production, from a rock mechanics vantage point, are related to the characteristics of the natural fracture systems and their subsequent interaction with the induced fracturing. The dominant role of the in situ stresses and formation mechanical properties for reservoir site selection and hydraulic fracture treatment are quantified in this paper. An illustration of basement-sedimentary cover interaction and salient mechanisms responsible for stress reorientation and tectonic relief in the Rome trough region of the Appalachian Plateau is given. In addition, examples detailing Plateau is given. In addition, examples detailing induced fracture dimension evaluations along with a discussion of factors governing fracture width, vertical fracture migration and fracture length are presented. Finally, the suitability of different presented. Finally, the suitability of different stimulation treatments is discussed.

Introduction

The Eastern Gas Shales Project (EGSP), since its inception in 1976, has been developing optimum stimulation methods and supporting rationale for gas production from the eastern petroliferous basins. It production from the eastern petroliferous basins. It is anticipated that unconventional gas resources from the Devonian shales can provide a healthy increment of energy in the near future. As an integral part of this program, fifty-nine wells in eight states (KY, MI, NY, OH, PA, VA, WV, and TN) have been stimulated to date with treatments such as massive hydraulic fracturing, cryogenic fracturing, dendritic fracturing foam fracturing, and displaced chemical explosive fracturing. Supportive small scale and modeling studies are also being conducted by government laboratories and universities.

The above investigations are defining a focused strategy for stimulating reservoirs in the Appalachian basin where by the natural fracture systems can be optimally linked to the well bore for gas recovery. The importance of natural fracture systems as communication channels for gas has been documented by several investigators. The frequency, extent, and preferred orientations of natural fracture and joint preferred orientations of natural fracture and joint systems is a function of complex geomechanical relationships such as basement-sedimentary interactions, multi-layering, anisotropies, and resulting in situ stress gradients. To fully exploit these fracture systems, the selected stimulation treatments and their design are based on reservoir and rock mechanics parameters. The available data indicates that in Devonian parameters. The available data indicates that in Devonian shale formations with sparse natural fracture systems, foam fracturing primarily is a cost effective stimulation technique. Tailored pulse explosive or non-conventional hydraulic fracture techniques (foam, dendritic, cryogenic), based on site specific characteristics and production objectives, appear desirable for medium to high natural fracture density regimes.

The objective of this investigation is to highlight the critical role of rock mechanics in potentially optimizing gas production from the Appalachian basin. potentially optimizing gas production from the Appalachian basin. The paper is essentially organized in two parts. Firstly, evaluations of the mechanisms responsible for in situ stress reorientation and stress trajectory magnitudes are initially conducted. This study delineates possible zones with tectonic relief and high natural fracture density. Secondly, the prediction of hydraulically induced vertical fracture dimensions is presented in terms of in situ stresses, formation presented in terms of in situ stresses, formation properties, and frac fluid flow variables. In addition, properties, and frac fluid flow variables. In addition, the potential use of different site selection treatments is discussed.

IN SITU STRESS TRAJECTORY EVALUATIONS

Since gas production from the shales correlates with the extent of fracture systems connected to the well bore, the determination of the reservoir in situ stress state along with preferential orientations for induced fracturing is important. Several stress mediated mechanisms that generate endogenous and exogenous fractures have been postulated in the literature.

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