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ATTACHMENT A:AREA OF REVIEW METHODS <br /> TABLE A-4 <br /> Allowable Pressure Increase Variables <br /> Variable Description Value <br /> APallowable Allowable Pressure Increase, pounds per square inch 175 psi <br /> PH Hydrostatic Pressure of Mud Column, pounds per square inch 141 psi <br /> PG Pressure for Mud Displacement 34 psi <br /> H Depth of Mud Column, feet 4,100 ft <br /> proud Density of mud, pounds per gallon 9 ppg <br /> GS Gel Strength, pounds/100 ft2 20 Ib/100 ft <br /> D Diameter of Borehole, inches 8 in <br /> Based on 30 years of future injection <br /> Pressure Build-Up Calculations <br /> In order to determine the zone of endangering influence defined as the distance where <br /> pressure increase is greater than the calculated allowable pressure increase,the following <br /> equation and values for variables was used. <br /> Formation pressure can be calculated at specific times and distances from the injection well <br /> using the following equation(Matthews and Russell,1967). <br /> P�r,t�= P + 162.6QuB[log( <br /> kt 2 —3.23+0.87s�l <br /> kh O,ucr J <br /> Solving the above equation for various times and applying the principle of superposition, <br /> the estimated pressure at each of the wells,STIG-1 and LEC-1,can be estimated. Table A-3 <br /> and Figure A-1 show expected pressures at the wells,including the effects of interference. <br /> Figure A-2 shows the calculated pressure increase at LEC-1 over a 30-year period, and <br /> Figure A-3 compares calculated formation pressures to estimated fracture pressure at the <br /> site. <br /> Based on the fracture gradient of 0.73 psi/ft and a top perforation depth of 4,234 ft,the <br /> fracture pressure is 2,993 psi. Initial formation pressure is approximately 1,857 psi. Based on <br /> parameter values used in the above equations,the pressure increase in the injection zone is <br /> expected to remain well below fracture pressure after continuous injection at proposed rates <br /> for 10 years. <br /> Applying the equation for the total site injection rate of 425 gpm for 30 years,pressure <br /> increase vs. distance from the site can be plotted as shown in Figure A-4. <br /> As shown in Figure A-4,the distance where the pressure increase exceeds the allowable <br /> value is approximately 1.16 miles. <br /> SAC/371322/082550016(ATTACH MENT-A.DOC) A-5 <br />