Gas production from the Barnett Shale relies on hydraulic fracture stimulation. Natural opening-mode fractures reactivate during stimulation and enhance efficiency by widening the treatment zone. Knowledge of both the present-day maximum horizontal stress, which controls the direction of hydraulic fracture propagation, and the geometry of the natural fracture system, which we discuss here, is therefore necessary for effective hydraulic fracture treatment design. We characterized natural fractures in four Barnett Shale cores in terms of orientation, size, and sealing properties. We measured a mechanical rock property, the subcritical crack index, which governs fracture pattern development. Natural fractures are common, narrow (0.05 mm; 0.002 in.), sealed with calcite, and present in en echelon arrays. Individual fractures have high length/width aspect ratios (1000:1). They are steep (75), and the dominant trend is west-northwest. Other sets trend north-south. The narrow fractures are sealed and cannot contribute to reservoir storage or enhance permeability, but the population may follow a power-law size distribution where the largest fractures are open. The subcritical crack index for the Barnett Shale is high, indicating fracture clustering, and we suggest that large open fractures exist in clusters spaced several hundred feet apart. These fracture clusters may enhance permeability locally, but they may be problematic for hydraulic fracture treatments. The smaller sealed fractures act as planes of weakness and reactivate during hydraulic fracture treatments. Because the maximum horizontal stress trends northeast-southwest and is nearly normal to the dominant natural fractures, reactivation widens the treatment zone along multiple strands.

Natural fractures in the Barnett Shale and their importance for hydraulic fracture treatments

What Is Stimulated Reservoir Volume

Thirty Years of Gas Shale Fracturing: What Have We Learned?

Identification of risk, the potential for occurrence of an event and impact of that event, is the first step in improving a process by ranking risk elements and controlling potential harm from occurrence of a detrimental event. Hydraulic Fracturing has become a hot environmental discussion topic and a target of media articles and University studies during development of gas shales near populated areas. The furor over fracturing and frac waste disposal was largely driven by lack of chemical disclosure and the pre2008 laws of some states. The spectacular increase in North American natural gas reserves created by shale gas development makes shale gas a disruptive technology, threatening profitability and continued development of other energy sources. Introduction of such a disruptive force as shale gas will invariably draw resistance, both monetary and political, to attack the disruptive source, or its enabler; hydraulic fracturing. Some ―anti-frack‖ charges in media articles and university studies are based in fact and require a stateby-state focused improvement of well design specific for geology of the area and oversight of overall well development. Other articles have demonstrated either a severe misunderstanding or an intentional misstatement of well development processes, apparently to attack the disruptive source. Transparency requires cooperation from all sides in the debate. To enable more transparency on the oil and gas side, both to assist in the understanding of oil and gas activities and to set a foundation for rational discussion of fracturing risks, a detailed explanation of well development activities is offered in this paper, from well construction to production, written at a level of general public understanding, along with an initial estimation of frac risk and alternatives to reduce the risk, documented by literature and case histories. This discussion is a starting point for the well development descriptions and risk evaluation discussions, not an ending point. Introduction to Risk There are no human endeavors without risk. ―Risk management is the identification, assessment and prioritization of risks followed by coordinated and economical application of resources to minimize, monitor and control probability and/or impact of unfortunate effects‖ (Wikipedia). Managing these risks and communicating both risks and changes to reduce risks are part of an often repeated approach termed ―license to operate‖ (Liroff, 2011). At a minimum, basic risk concerns are: People, Economic Loss (to all concerned), Environmental Damage and Reputation Loss. Figure 1, a standard loss matrix used by Apache Canada in the Horn River development (DeMong, 2010), is a good starting place for the discussion. Consequences run from slight and practically unavoidable to severe and avoidable at all costs. This paper, for purposes of brevity, will focus solely on risk to the environment from hydraulic fracturing operations, starting with transport of materials and ending when the well is routed to the production facilities and gas sales begin. The form of Figure 1 will be expanded and comments and

Hydraulic Fracturing 101: What Every Representative, Environmentalist, Regulator, Reporter, Investor, University Researcher, Neighbor and Engineer Should Know About Estimating Frac Risk and Improving Frac Performance in Unconventional Gas and Oil Wells

Reservoir Modeling in Shale-Gas Reservoirs

Optimizing Horizontal Completion Techniques in the Barnett Shale Using Microseismic Fracture Mapping

The Barnett shale of north Texas is an ultralow-permeability reservoir that must be fracture stimulated to obtain commercial production. Techniques to optimize hydraulic-fracturing effectiveness have evolved over the past decade. In 2002, the Newark East field produced 202 Bcf, the seventh largest gas producer in the U.S. This pilot study compared production from the first 23 horizontal wells in a core area of the Fort Worth basin with vertical wells in the same area. Drilling and completion strategies, fracture-network areas, and fracture effectiveness were compared with the standard procedures used in vertical Barnett wells.

J. R. Heinze

Papers

Optimizing Horizontal Completion Techniques in the Barnett Shale Using Microseismic Fracture Mapping

Optimizing horizontal completions in the Barnett shale with microseismic fracture mapping