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<br />CRAPTERTWO Proposed Action and Alternatives <br />supply heat and pressure to the cavity to effectively mine, and how to develop travel pathways <br />within the oil shale matrix, etc. are unknown at this time. <br />2.5.2.2 Directiona- Drilling <br />During the planning and preliminary design process for the Yankee Gulch Project, several parties <br />raised the possibility of directional drilling. The general concept was that directional drilling <br />could be used to establish multiple wells from a single well pad. Theoretically, this could reduce <br />the surface disturbance associated with well development and could allow mining under steep <br />slope areas that could not otherwise be accessed without lazge cut and fill disturbances for well <br />pads. <br />Directional drilling technology is promising and may have a viable application to American <br />Soda's operations in the future. Directional drilling has been used in oil and gas recovery to <br />access areas for fracturing and subsequent collection of fossil fuels. However, there aze several <br />important technical differences between these applications and American Soda's proposed <br />mining. Because directional drilling has several technical limitations and has not been tested in <br />this type of mining, it is not currently a viable alternative to single-well vertical drilling for this <br />project. <br />There are two types of directional drilling that could potentially be used by American Soda, <br />incline drilling and vertical-offset drilling (Figure 2-16). Incline drilling essentially rotates the <br />drill hole and cavity at an angle from the pad. The growth chazacteristics and geometry of an <br />angled cavity aze unknown. For example, whether the cavity would grow symmetrically and <br />whether the upwazd growth of the cavity could be controlled are unknown. These unknowns and <br />' the angled-cavity orientation make the interpretation of underground stability and potential for <br />inter-cavity communication impossible. Consequently, a stable spacing pattern for cavities <br />cannot be developed. The orientation of tubing strings in an angled hole also makes the potential <br />for damage or destruction of the tubing from rock movement much higher than in a vertical hole. <br />Vertical offset drilling would involve the use of an s-shaped bore hole to create a vertical cavity <br />that is offset from the neighboring cavity (Figure 2-16). Although this method would alleviate <br />the cavity growth and geometry unknowns, there aze substantial difficulties in installing casing <br />and tubing strings in an s-shaped hole. A principal problem is adequately cementing the casing <br />to protect the aquifer system. Cementing techniques for the complex well completion required <br />by American Soda in an s-shaped hole are unproven and may be impossible. Thus, the s-shaped <br />hole may not be able to be adequately isolated from the aquifer. Construction of the tubing <br />system is problematic primarily due the potential for damage or destruction of the tubing from <br />rock movement. <br />' The drilling costs for directional drilling are expected to be three to five times higher than <br />conventional drilling. The substantially higher costs coupled with the technical limitations and <br />uncertainties make directional drilling inviable for application in American Soda's commercial <br />mining at this time. However, the concept of directional drilling holds promise and may become <br />a viable application in the future. American Soda is interested in directional drilling and would <br />continue to evaluate it as the technology advances. <br />2-37 <br />