Applying Hydraulic Fracture Diagnostics to Optimize Stimulations in the Woodford Shale

Abstract

The success of the Barnett Shale has many operators in search of similar producing formations. One such formation is the Woodford Shale which stretches from Kansas to west Texas. The Woodford is an ultra-low permeability reservoir that must be effectively fracture stimulated in order to obtain commerical production. Once a formation that was drilled through on the way to deeper horizons, this shale play now dominates drilling activity in southeast Oklahoma. Like the Barnett, initial testing of the Woodford Shale was from existing vertical wells that penetrated deeper horizons. Currently, the main exploitation of the Woodford Shale is from long horizontal wells with some lateral lengths exceeding 4000 ft. The wells are stimulated in stages with large hydraulic fracture treatments. Successful shale plays have demonstrated that production is directly related to the size of the stimulated reservoir volume. Techniques to optimize hydraulic fracturing effectiveness have been evolving in the area the last few years. Over 100 frac stages have been mapped in the Woodford Shale using surface tiltmeters, offset-well microseismic and treatment-well microseismic mapping techniques. This paper will examine the effect of lateral azimuth, formation dip and its influence on asymmetric fracture growth; the effect of existing faults and its interaction with the fracture stimulation. Additionally, stimulation size, number of stages, perforation clusters and fracture initiation problems will be discussed. Finally, a comparison to Barnett Shale type fracture networks will be made. Understanding fracture growth in the Woodford Shale willl enhance the development of the play by helping operators optimize fracture completion and well placement strategies. Overview of the Woodford Shale The Woodford Shale is of Devonian age and extends from southern Kansas, through Oklahoma and into west Texas. It is found within the black shale belt as show in Figure 1. It is easily identified by a very high gamma ray streak and is 50–300 ft thick as shown in Figure 2. Completions have been made from depths of 900 ft in northeast Oklahoma to 13,000 ft in west Texas. A typical core contains: 35–50% quartz, 0–20% calcite/dolomite, 0–20% pyrite, and 10–50% total clay. Porosity ranges from 3–9% and permeability ranges from 0.000001 md to 0.001 md. Water saturation varies from 30% to 45%. The formation is slight underpressured with pressure gradients in the 0.35 to 0.44 psi/ft range. The Woodford Shale was first produce in 1939 in southeast Oklahoma. Drilling activity that targeted the Woodford Shale as the primary objective was slow to grow. By late 2004 there were only 22 Woodford shale completions. By the end of 2006 there were 143 Woodford Shale completions.[1,2] Through mid year 2007, there had been an additional 176 wells drilled with an estimated total of 350 wells for the year (see Figure 3).

Integrating Microseismic Monitoring With Well Completions, Reservoir Behavior, and Rock Mechanics

“…The fracture intersects a fault about ¾ of the distance to the monitor well in the upper left corner and it begins to emit very large microseisms (hot colors) and turns direction by about 45°. Similar redirected fractures were observed at Jonah and in the Woodford shale (Vulgamore et al 2007). A clear understanding whether some particular behavior is fault related or normal fracture behavior can be critical in deciding how to proceed with a stimulation campaign in a given reservoir or in a given field.…”

“…The primary tool for understanding the interaction of all of these factors has been microseismic monitoring. Numerous studies have been performed examining fracture treatments in these reservoirs (Fisher et al 2002, Maxwell et al 2002, Griffin et al 2003, Sharma et al 2004, Cipolla et al 2005, Fontaine et al 2005, Mayerhofer et al 2005, Wolhart et al 2006, Shemeta et al 2007, Vulgamore et al 2007, Daniels et al 2007, King et al 2008, Potapenko et al 2009, Waters et al 2009), although only a few also provide the final link with production.…”

Simultaneous Multifracture Treatments: Fully Coupled Fluid Flow and Fracture Mechanics for Horizontal Wells

“…Stress-shadow effects strongly depend on the net pressure within the fractures (Pollard and Segall 1987;Warpinski and Branagan 1989). Larger net pressure will lead to stronger stress-shadow effects.…”

Cement Technology Improves Fracture Initiation and Leads to Successful Treatments in the Eagle Ford Shale

“…The use of ASC minimizes this effect because the ASC dissolves around the perforation cluster on acidizing with HCl acid to produce conditions approaching that of an uncemented lateral or open hole, while leaving cement between perforation clusters to provide annular isolation and wellbore stability. Near-wellbore fracture-complexity issues experienced during the stimulation treatment can be addressed with a cementing program by using ASC (McDaniel et al 1999, Vulgamore et al 2007.…”