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OIL/GAS WELL MULTIRATE DRAWDOWN PROGRAM DOCUMENTATION ----------------------------------------------------- PROGRAM DESCRIPTION ------------------- PURPOSE: TO ANALYZE VARIABLE RATE FLOW DATA FOR HYDRAULICALLY FRACTURED WELLS, ACIDIZED WELLS, OR NATURAL COMPLETIONS. THE PROGRAM DETERMINES PERMEABILITY, SKIN FACTOR, FRACTURE HALF LENGTH, FRACTURE CAPACITY, RESERVOIR SIZE, TIME REQUIRED TO REACH REACH BOUNDARY, AND DIETZ SHAPE FACTOR. FOR GAS WELLS IT WILL ALSO ANALYZE WELLBORE/FRACTURE STORAGE VOLUME AND TURBULENCE. OPTIONS: (1) FRACTURE FLOW ANALYSIS - FOR FRACTURED WELLS WITH LIMITED CONDUCTIVITY FRACTURES, IT WILL DETERMINE FRACTURE HALF LENGTH AND FRACTURE CAPACITY (ACTUAL & DIMENSIONLESS). (2) RADIAL FLOW ANALYSIS - FOR NATURAL COMPLETIONS OR FRACTURED WELLS IN TRANSIENT PSEUDORADIAL FLOW, IT WILL DETERMINE PERMEABILITY, SKIN FACTOR, EFFECTIVE WELLBORE RADIUS, STORAGE VOLUME, AND NON-DARCY FLOW COEFFICIENT. (3) PSEUDO STEADY STATE ANALYSIS - IT WILL DETERMINE THE RESERVOIR SIZE, RESERVES IN PLACE, RADIUS OF DRAINAGE, AND DIETZ SHAPE FACTOR. INPUT: INITIAL RESERVOIR PRESSURE PRESSURE DRAWDOWN TEST DATA (TIMES, B.H. PRESSURES AND RATES) RESERVOIR TEMPERATURE TOTAL POROSITY, CRITICAL WATER SATURATION & NET PAY ADDITIONAL INPUT FOR GAS WELLS: GAS GRAVITY DEPTH AND FLOWSTRING I.D. (I.E. WELLBORE STORAGE VOLUME) FRACTURE STORAGE VOLUME NON-DARCY FLOW COEFFICIENT (F) ADDITIONAL INPUT FOR OIL WELLS: OIL FORMATION VOLUME FACTOR OIL VISCOSITY OIL COMPRESSIBILITY OUTPUT: PERMEABILITY SKIN FACTOR & EFFECTIVE WELLBORE RADIUS FRACTURE HALF LENGTH & FRACTURE CAPACITY PROVED RESERVOIR SIZE (ACRES, DRAINAGE RADIUS, AND RESERVES) TIME REQUIRED TO REACH RESERVOIR BOUNDARY DIETZ SHAPE FACTOR USES: (1) CAN ANALYZE GAS WELLS, GAS/CONDENSATE WELLS, OIL WELLS, OIL/WATER WELLS, AND WATER WELLS. (2) CAN ANALYZE VARIABLE FLOW RATE DATA FROM ANY SOURCE, INCLUDING DRILL STEM TESTS, COMPLETION REPORTS, DAILY GAUGE REPORTS, FOUR POINT TESTS & BOTTOM HOLE BOMBS. EVEN SHUT INS CAN BE INCLUDED WITHIN THE FLOW DATA. (3) CAN DETERMINE THE NEED OR EFFECTIVENESS OF STIMULATION IN TERMS OF THE SKIN FACTOR, FRACTURE LENGTH, FRACTURE CONDUCTIVITY, AND THE EFFECTIVE WELLBORE SIZE. (4) CAN DETERMINE THE INSITU PERMEABILITY OF THE RESERVOIR. (5) RESERVOIR SIZE CAN BE DETERMINED FASTER THAN CONVENTIONAL METHODS (P/Z FOR GAS OR MATERIAL BALANCE FOR OIL). (6) CAN USE RESULTS AS INPUT FOR GAS WELL RESERVOIR SIMULATOR THEORY: (1) PRESSURE FUNCTIONS ARE EVALUATED USING REAL GAS PSEUDO PRESSURES, I.E. THE M(P) FUNCTION OF AL-HUSSAINY. (2) TIME FUNCTIONS ARE EVALUATED USING SUPERPOSITION. (3) VARIABLE RATES ARE NORMALIZED USING THE THEORIES OF A.S. ODEH AND L.G. JONES. (3) PERMEABILITY AND SKIN FACTOR ARE EVALUATED BY PSEUDO HORNER ANALYSIS. (4) DIMENSIONLESS FRACTURE CONDUCTIVITY (Fcd) IS DEFINED BY AGARWAL (SPE #6838) AND GENERALLY RANGES FROM ABOUT 0.01 FOR VERY LOW CONDUCTIVITY FRACTURES TO ABOUT 500 FOR VERY HIGH CONDUCTIVITY FRACTURES. (5) FRACTURE PROPERTIES ARE EVALUATED USING CORRELATIONS DEVELOPED BY J. O. SCOTT WHICH RELATE THE TRANSIENT PRERADIAL LOG-LOG SLOPE TO FRACTURE CONDUCTIVITY AND FRACTURE HALF LENGTH. (6) WELLBORE STORAGE EFFECTS ARE ACCOUNTED FOR USING THE THEORIES OF H.J. RAMEY JR. AND R.E. GLADFELTER. (7) NON-DARCY FLOW FACTORS ARE EVALUATED USING THE THEORIES OF G.W. SWIFT, O.G. KIEL AND H.J. RAMEY JR. (8) RESERVOIR SIZE IS EVALUATED USING THE THEORIES OF PARK JONES AND R.C. EARLOUGHER, JR. (9) DIETZ SHAPE FACTOR IS EVALUATED USING THE THEORIES OF D.N. DIETZ. THIS SHAPE FACTOR USES INPUT FROM BOTH TRANSIENT AND PSEUDOSTEADY STATE FLOW. HENCE, IT SERVES AS AN EXCELLENT CHECK TO VERIFY THE REASONABLENESS OF THE SELECTION OF BOTH FLOW PERIODS. INSTALLATION INSTRUCTIONS ------------------------- THE DISK WHICH YOU PURCHASED MAY NOT HAVE ENOUGH FREE SPACE LEFT TO RUN THE DRAWDOWN.EXE MODULE. IN ORDER TO INSTALL THIS SOFTWARE PLEASE FOLLOW THESE STEPS: IF YOU HAVE A HARD DRIVE SIMPLY COPY THIS DISK TO YOUR HARD DRIVE THEN IT IS READY TO RUN. IF YOU DON'T HAVE A HARD DRIVE, THEN COPY DRAWDOWN.EXE ALONG WITH PLOT, TABL, AND CALC TO A SECOND FLOPPY DISK. THEN COPY EVERYTHING ELSE TO A THIRD FLOPPY DISK. WHEN YOU HAVE AN INPUT DATA FILE READY TO RUN THEN COPY IT TO THE SECOND FLOPPY DISK. THEN RUN DRAWDOWN.EXE FROM THE SECOND DISK. YOU MAY ALSO NEED TO COPY YOUR PRINT.COM TO THE SECOND DISK TO GET PRINTOUTS. DEFINITION OF INPUT VARIABLES ----------------------------- TOTAL POROSITY - IS THE POROSITY OBTAINED FROM WELL LOG INTERPRETATION CRITICAL WATER SATURATION FOR GAS WELLS - IF THE WELL DOES NOT PRODUCE ANY FLUIDS THEN USE THE INITIAL WATER SATURATION OBTAINED FROM THE LOGS. IF THE WELL PRODUCES FLUIDS THEN USE THE CRITICAL WATER SATURATION WHICH WILL BE LESS THAN THE INITIAL WATER SATURATION. CRITICAL WATER SATURATION FOR OIL WELLS - IF THE WELL DOES NOT PRODUCE ANY WATER THEN USE THE INITIAL WATER SATURATION OBTAINED FROM THE LOGS. IF THE WELL PRODUCES WATER THEN USE THE CRITICAL WATER SATURATION WHICH WILL BE LESS THAN THE INITIAL WATER SATURATION. CRITICAL WATER SATURATION FOR WATER WELLS - ALWAYS USE THE CRITICAL WATER SATURATION WHICH WILL BE LESS THAN THE INITIAL WATER SATURATION. EXECUTABLE MODULES ------------------ YOU WILL HAVE THE FOLLOWING EXECUTABLE MODULES: DRAWDOWN - THIS PERFORMS A VARIABLE RATE DRAWDOWN ANALYSIS ON ANY WELL. THIS IS THE MAIN MODULE WHICH WILL ANALYZE FLOW DATA FOR GAS WELLS, GAS/CONDENSATE WELLS, OIL WELLS, OIL/WATER WELLS, AND WATER WELLS. BE SURE THAT A DATA FILE ALREADY EXISTS FOR THE WELL YOU WANT TO ANALYZE BEFORE RUNNING THIS MODULE. DRAWDOWN DATA FILES CAN BE CREATED WITH EITHER DDINPUT1.EXE, DDINPUT2.EXE OR DDREPEAT.EXE WHICH ARE ALL EXPLAINED BELOW. IF YOU ARE GOING TO ANALYZE AN OIL WELL, AN OIL/WATER WELL, OR A WATER WELL THEN ALSO BE SURE THAT YOU HAVE RUN THE OILPROP.EXE MODULE FIRST IN ORDER TO DETERMINE THE NECESSARY FLUID PROPERTIES WHICH YOU WILL BE PROMPTED FOR. DDINPUT1 - USE THIS MODULE IF YOU HAVE DATA FROM A BOTTOM HOLE BOMB. YOU WILL BE PROMPTED FOR BASIC INFORMATION, AND EACH DATA FLOW POINTS CUMULATIVE TIME, FLUID RATES (OIL, GAS AND WATER), AND THE BOTTOM HOLE FLOWING PRESSURE. THIS MODULE CAN BE USED FOR GAS WELLS, GAS/CONDENSATE WELLS, WELLS, OIL WELLS, OIL/WATER WELLS, AND WATER WELLS. DDINPUT2 - THIS MODULE CAN ONLY BE USED FOR GAS WELLS OR FOR GAS/CONDENSATE WELLS. USE THIS MODULE IF YOU HAVE SURFACE FLOWING PRESSURES TO ANALYZE. THIS MODULE WILL ESTIMATE THE BOTTOM HOLE SHUTIN PRESSURES AND SAVE THEM IN THE INPUT DATA FILE. YOU WILL BE PROMPTED FOR BASIC INFORMATION, INITIAL RESERVOIR PRESSURE, AND OTHER PARAMETERS NEEDED TO CALCULATE BOTTOM HOLE PRESSURES FROM SURFACE PRESSURES SUCH AS WELL DEPTH, GAS GRAVITY, OIL GRAVITY, TUBING I.D., BOTTOM HOLE TEMP., ETC. THIS MODULE IS COMMONLY USED TO ANALYZE ROUTINELY COLLECTED PRODUCTION DATA REPORTED ON DAILY GAUGE REPORTS. THIS MODULE WILL ALLOW YOU TO ENTER THE TIME AS A DATE (MONTH, DAY & YR), IN DAYS, OR IN HOURS. DDREPEAT - THIS MODULE CAN ONLY BE USED FOR GAS WELLS OR FOR GAS/CONDENSATE WELLS. USE THIS MODULE IF YOU WANT TO ADJUST OR ADD ANY DATA. FOR EXAMPLE YOU CAN ADJUST THE DEPTH, TUBING ID, GAS GRAVITY, OIL API, RESERVOIR TEMP, PRESSURE DROP FACTOR, OR WELLHEAD SHUT IN PRESSURE. YOU CAN ALSO ADD NEW DATA POINTS WITH ANY TEXT EDITOR. THE ONLY FIELDS YOU NEED TO ENTER ARE GAS RATE, CHOKE, WHFP, BOPD, BWPD, AND DATE. THE DDREPEAT MODULE WILL RECALCULATE THE CUM DAYS, BHFP, Z, BHP/Z, CUM GAS, CUM GE, GIP, AND GE GIP FOR ALL DATA POINTS. IT WILL ALSO RECALCULATE THE IBHSIP, Zi, AND P/Zi. THIS MODULE CAN ONLY BE USED IF THE DRAWDOWN DATA FILE CONTAINS THE MONTH, DAY & YEAR FIELDS. OILPROP - THIS MODULE IS USED TO ESTIMATE THE RESERVOIR FLUID PROPERTIES IF A FLUID ANALYSIS IS NOT AVAILABLE. IT USES STANDARD CORRELATIONS TO ESTIMATE FLUID PROPERTIES SUCH AS FORMATION VOLUME FACTOR, COMPRESSIBILITY, AND VISCOSITY FOR BOTH OIL AND WATER. IT CAN ALSO BE USED TO ESTIMATE THE INITIAL BUBBLE POINT PRESSURE IF IT IS NOT KNOWN. IN ORDER TO GET A PRINTOUT OF THE RESULTS BE SURE TO TYPE "Ctrl-PrtSc" PRIOR TO RUNNING THIS MODULE. BE SURE TO TYPE "Ctrl-PrtSc" AGAIN WHEN YOU ARE FINISHED. DATA FILES ---------- YOU WILL HAVE THE FOLLOWING INPUT DATA FILES: GASWELL.DD (SAMPLE GAS DRAWDOWN ANALYSIS) ------------------------------------------ YOU MAY WANT TO LEARN TO USE THIS PROGRAM BY USING THIS SAMPLE DATA FILE. IF YOU DO THEN USE THE FOLLOWING INPUT PARAMETERS: GAS GRAVITY (0.576), BOTTOM HOLE TEMP (284 F), API OIL GRAVITY (60 DEG), FRACTIONAL WATER SATURATION (0.30), TOTAL FRACTIONAL POROSITY (0.0782), NET PAY (34 FT), WELL DEPTH (14907 FT), TUBING I.D. (2.441 IN.) & INITIAL RESERVOIR PRESSURE (12435 PSI). IF YOU HAVE A DEMO DISK, THEN SOME OF THESE PARAMETERS WILL NOT BE ABLE TO BE CHANGED EVEN FROM THE PROMPTS. OTHERWISE, THE DEMO DISK WILL DO EVERYTHING ELSE THE ACTUAL PROGRAM DOES. REASONABLE POINTS TO SELECT FROM FIGURE 3 ARE J AND L. REASONABLE POINTS TO SELECT FROM FIGURE 2 ARE N AND P. REASONABLE POINTS TO SELECT FROM FIGURE 4 ARE A AND E. NOTE THAT THE POINTS ARE CASE SENSITIVE. THIS DATA COMES FROM DAILY GAUGE REPORTS ON AN ACTUAL GAS WELL DRILLED ON 640 ACRE SPACING. YOU SHOULD OBTAIN A RESERVOIR SIZE CLOSE TO 640 ACRES. THE PERMEABILITY SHOULD BE ABOUT 0.20 MD WITH A SKIN OF ABOUT -5.3. OILWELL.DD (SAMPLE OIL DRAWDOWN ANALYSIS) ----------------------------------------- YOU MAY WANT TO LEARN TO USE THIS PROGRAM BY USING THIS SAMPLE DATA FILE. IF YOU DO THEN USE THE FOLLOWING INPUT PARAMETERS: FVF or Bo (1.25), RESERVOIR PRESSURE (3253 PSI), BOTTOM HOLE TEMP (260 F), FRACTIONAL WATER SATURATION (0.25), TOTAL FRACTIONAL POROSITY (0.15), NET PAY (30 FT), OIL VISCOSITY (1.0), AND OIL COMPRESSIBILITY (12.5). IF YOU HAVE A DEMO DISK, THEN SOME OF THESE PARAMETERS WILL NOT BE ABLE TO BE CHANGED EVEN FROM THE PROMPTS. OTHERWISE, THE DEMO DISK WILL DO EVERYTHING ELSE THE ACTUAL PROGRAM DOES. REASONABLE POINTS TO SELECT FROM FIGURE 3 ARE A AND D. REASONABLE POINTS TO SELECT FROM FIGURE 2 ARE D AND F. REASONABLE POINTS TO SELECT FROM FIGURE 4 ARE A AND B. NOTE THAT THE POINTS ARE CASE SENSITIVE. NEW DATA FILES WITH THE SAME FORMAT AS THOSE INCLUDED CAN BE CREATED BY EXECUTING EITHER DDINPUT1 OR DDINPUT2. WHEN CREATING A NEW INPUT DATA FILE WITH EITHER DDINPUT1 OR DDINPUT2 ENTER UP TO AN 8 CHARACTER ALPHANUMERIC NAME FOLLOWED BY A PERIOD AND UP TO A 3 CHARACTER ALPHANUMERIC NAME. FOR EXAMPLE IF THE NAME OF THE WELL YOU ARE GOING TO ANALYZE IS ANNA #1-12, THEN FOR AN INPUT FILE NAME YOU MIGHT ENTER "ANNA1-12.DD" AT THE PROMPT. DATA LIMITATIONS ---------------- A MAXIMUM OF 365 FLOW DATA POINTS MAY BE USED BY THE PROGRAM FOR AN ANALYSIS. HOWEVER, A MAXIMUM OF 1000 FLOW DATA POINTS MAY BE IN THE INPUT DATA FILE. DATA POINTS MAY BE SKIPPED FROM BEING READ BY THE PROGRAM BY SIMPLY TYPING " SKIP" IMMEDIATELY AFTER AN INPUT LINE IN THE DATA FILE AS SHOWN IN THE SAMPLE DATA FILE BELOW. THIS IS DONE AFTER THE INPUT FILE IS CREATED WITH ANY TEXT EDITOR. IT IS COMMON TO SKIP DATA POINTS WHICH ARE ADJACENT TO ONE ANOTHER AND HAVE APPROXIMATELY THE SAME VALUES FOR RATE, PRESSURE AND TIME IF YOU ARE CONSTRAINED BY THE 180 DATA POINT LIMITATION. TWO CONSECUTIVE SHUT IN DATA POINTS ARE NOT ALLOWED. IF YOU HAVE ALREADY CREATED YOUR DATA FILE WITH THESE POINTS SIMPLY PUT A "SKIP" ON ALL BUT THE LAST SHUTIN POINT FOR EACH GROUP OF SHUT INS. SAMPLE DATA FILE ---------------- BELOW IS PART OF THE OILWELL.DD INPUT DATA FILE. IT DEMONSTRATES HOW TO SKIP SELECTED INPUT DATA POINTS FROM BEING ANALYZED. NOTE THAT ONLY THE DATA POINT AT .015 DAYS IS SKIPPED SINCE IT HAS "SKIP" IN THE SKIP FIELD. ALL THE REST OF THE POINTS ONLY HAVE "SK P". OILWELL #1 BLACK GOLD OIL CO. SEC 3-12N-18W CUSTER CO., OK. 3253.0 = EST BHSIP RED FORK 01/01/91 INITIAL FLOW TEST CUM DAYS MCFD BHFP SKIP CHOKE WHFP BOPD BWPD .015 .0 3216.0 SKIP 850.0 .0 .031 .0 3198.0 SK P 830.0 .0 .059 .0 3180.0 SK P 825.0 .0 .133 .0 3154.0 SK P 820.0 .0 .206 .0 3141.0 SK P 810.0 .0 .290 .0 3130.0 SK P 805.0 .0 .454 .0 3116.0 SK P 800.0 .0 .682 .0 3106.0 SK P 795.0 .0 .935 .0 3097.0 SK P 790.0 .0 OUTPUT FILES CREATED -------------------- THE FOLLOWING OUTPUT FILES WILL BE CREATED WHEN YOU RUN THE DRAWDOWN.EXE MODULE: PLOT - IS A DATA FILE CREATED IF YOU SAVE ANY PLOTS TO A FILE. THERE IS ALSO AN OPTION TO SEND PLOTS DIRECTLY TO THE PRINTER. IF YOU SEND THE PLOTS DIRECTLY TO THE PRINTER THEN BE SURE TO RUN "PRINTER.COM" FIRST BEFORE RUNNING "DRAWDOWN". THE PRINTER PLOTS WILL CONTAIN MUCH HIGHER RESOLUTION PLOTS OF FIGURES 1 THRU 4 THAN THE SAME PLOTS SHOWN ON THE COMPUTER SCREEN. THE STABILIZATION FACTOR SHOWN IN FIGURE 1 REPRESENTS A MEASURE OF THE CONFIDENCE OF A PARTICULAR DATA FLOW POINT. A VALUE OF 1.0 WILL REPRESENT THE BEST CONFIDENCE. VALUES ABOVE 1.0 ARE GENERALLY DUE TO STORAGE EFFECTS. VALUES BELOW 1.0 ARE GENERALLY DUE TO LATE TIME SUPERPOSITION EFFECTS. WHEN SELECTING POINTS TO USE, ALWAYS CHECK THE VALUE OF THE STABILIZATION FACTOR FOR THE POINTS YOU WANT TO SELECT. ALL SCALING FOR THE PLOTS IS DONE AUTOMATICALLY. ONLY THE LAST 52 DATA POINTS WILL HAVE UNIQUE SYMBOLS ON THE PLOTS. THE LAST DATA POINT USED IN YOUR INPUT FILE WILL ALWAYS BE THE PLOT SYMBOL "A". THE LAST 26 DATA POINTS WILL ALL BE CAPITAL LETTERS. THE 26 DATA POINTS BEFORE THESE WILL ALL BE LOWERCASE LETTERS. IF YOU WANT TO USE ANY POINTS BEFORE THE LAST 52 DATA POINTS (I.E. THOSE WITH PLOT SYMBOL "*") THEN YOU MUST MATCH UP THE VALUES ON THE PLOT WITH THE VALUES PRINTED ON "TABL", AND THEN REFER TO THIS DATA POINT AS A NUMBER INSTEAD OF A LETTER SYMBOL. TABL - IS A DATA FILE ALWAYS CREATED WHEN YOU RUN THE DRAWDOWN MODULE. IT CREATES THE REPORTS CALLED "GAS WELL VARIABLE RATE DRAWDOWN DATA" FOR GAS OR "OIL WELL VARIABLE RATE DRAWDOWN DATA" FOR OIL. CALC - IS A DATA FILE CREATED WHEN YOU USE THE CALCULATION OPTION TO ESTIMATE PERMEABILITY, SKIN FACTOR, DRAINAGE RADIUS, DIETZ SHAPE FACTOR, ETC. IT CREATES THE REPORTS "GAS WELL VARIABLE RATE DRAWDOWN CALCULATIONS" OR "OIL WELL VARIABLE RATE DRAWDOWN CALCULATIONS". THERE ARE THREE OPTIONS AVAILABLE FOR THE DRAWDOWN CALCULATIONS. OPTION 1 IS FOR RELATIVELY CONSTANT FLOW RATES OR GRADUALLY DECLINING FLOW RATES WITH VERY MINOR SHUT IN PERIODS IF ANY. IF THE RATES VARY WIDELY OR IF THERE ARE SIGNIFICANT SHUT IN PERIODS, USE OPTION 3. USE OPTION 2 IF SOMEWHERE BETWEEN THESE FLOW PATTERNS. BE SURE THAT THE PLOTS YOU ARE USING WERE GENERATED WITH THE SAME FLOW OPTION (1,2,3) YOU ARE USING FOR THE CALCULATIONS. IF THE WELL HAS FLOWED FOR A SIGNIFICANT AMOUNT OF TIME PAST THE TIME TO REACH THE BOUNDARY (I.E. PSEUDO STEADY STATE FLOW), THEN YOU SHOULD ALWAYS USE OPTION 1. ALSO NOTE THAT ONLY FIGURE 4 WILL CHANGE WITH CHANGING OPTIONS. PRINTING OUTPUT FILES --------------------- YOU WILL COMMONLY WANT TO PRINT THE FOLLOWING OUTPUT DATA FILES: PLOT - FIGURES 1 THRU 4 (UNLESS YOU PRINTED DIRECTLY TO PRINTER) TABL - VARIABLE RATE DRAWDOWN DATA CALC - VARIABLE RATE DRAWDOWN CALCULATIONS WHEN PRINTING THESE THREE OUTPUT DATA FILES, YOUR PRINTER SHOULD BE SET TO PRINT WIDE (ABOUT 130 CHARACTERS PER LINE). FOR NARROW PRINTERS THIS MEANS YOU SHOULD BE IN COMPRESSED PRINT MODE. I COMMONLY PRINT "TABL" AND "CALC" WITH COMPRESSED MODE AND 1/8" LINE SPACING, I.E. 8 LINES PER INCH. I COMMONLY PRINT "PLOT" WITH COMPRESSED MODE AND 4/72" LINE SPACING, I.E. 18 LINES PER INCH. FOR HP LASER JETS I USE 16 LINES PER INCH. YOU CAN SET LINE SPACING WITH A SIMPLE BASIC PROGRAM IF YOU KNOW THE COMMANDS FOR YOUR PRINTER. I HAVE INCLUDED A SAMPLE BASIC PROGRAM WHICH SETS THE LINE SPACING FOR EPSON PRINTERS AND HP LASER PRINTERS. PANASONIC PRINTERS CAN USE THE EPSON OPTION. TO USE THIS BASIC PROGRAM TYPE "BASIC PRINTER". THEN ENTER "1" FOR EPSON OR "2" FOR HP LASER JET. THEN ENTER "1" IF YOU ARE GOING TO PRINT "TABL" OR "CALC". ENTER "2" IF YOU ARE GOING TO PRINT "PLOT". BE SURE THAT BASIC.EXE IS IN YOUR PATH. AN EXECUTABLE VERSION OF THE PRINTER SETUP PROGRAM IS ALSO INCLUDED. IT IS CALLED "PRINTER.COM". SOURCE CODE IS CALLED PRINTER.PAS. CONSIDERATIONS WHEN RUNNING THE PROGRAM --------------------------------------- WHAT VALUE TO USE FOR INITIAL RESERVOIR PRESSURE ------------------------------------------------ THE VALUE YOU CHOOSE FOR INITIAL RESERVOIR PRESSURE IS VERY IMPORTANT FOR ACCURATE CALCULATIONS. A GOOD RULE OF THUMB IS THAT A TYPICAL FLUID GRADIENT IS 0.43 PSI/FT. FOR EXAMPLE, A WELL AT A DEPTH OF 10,000 FEET WOULD HAVE AN INITIAL RESERVOIR PRESSURE OF 4300 PSI IF NORMALLY PRESSURED. HOWEVER, MOST RESERVOIRS ARE EITHER UNDER PRESSURED OR OVER PRESSURED. STABILIZATION FACTOR -------------------- THE STABILIZATION FACTOR IS SHOWN ON FIGURE 1. IT IS SIMPLY THE ACTUAL TIME DIVIDED BY THE SUPERPOSITION OF TIME FOR A GIVEN DATA POINT. IF A WELL IS FLOWING AT CONSTANT RATE WITHOUT ANY STORAGE EFFECTS, THEN THE STABILIZATION FACTOR WILL ALWAYS BE "1.0". HOWEVER, TYPICALLY THE STABILIZATION FACTOR WILL START OUT NEAR "1.0" AND GRADUALLY DECLINE WITH TIME. THE STABILIZATION FACTOR IS USEFUL TO HELP IN SELECTING VALID DATA POINTS FOR ANALYSIS. POINTS WHICH DEVIATE SIGNIFICANTLY FROM "1.0" OR WHICH DEVIATE SIGNIFICANTLY FROM ADJACENT POINTS SHOULD NOT BE SELECTED FOR ANALYSIS. CHOICE OF FLOW OPTIONS ---------------------- OPTION 1 IS FOR RELATIVELY CONSTANT FLOW RATES OR GRADUALLY DECLINING FLOW RATES WITH VERY MINOR SHUTIN PERIODS IF ANY. THE PSEUDO STEADY STATE PLOT WILL USE ACTUAL TIME IN HOURS FOR RESERVE ANALYSIS. THIS METHOD WILL ALWAYS UNDERESTIMATE RESERVES AFTER THE BOUNDARY IS REACHED. OPTION 3 IS FOR WIDELY VARYING FLOW RATES OR FLOW RATES WITH PERIODIC SHUTINS BETWEEN FLOW PERIODS. THE PSEUDO STEADY STATE PLOT WILL USE THE SUPERPOSITION OF TIME IN FOR RESERVE ANALYSIS. THIS METHOD WILL ALWAYS OVERESTIMATE RESERVES AFTER THE BOUNDARY IS REACHED. OPTION 2 IS FOR A FLOW PATTERN SOMEWHERE IN BETWEEN OPTION 1 AND 3. THE PSEUDO STEADY STATE PLOT WILL USE THE AVERAGE OF ACTUAL TIME AND SUPERPOSITION OF TIME FOR RESERVE ANALYSIS. ALL THREE OPTIONS USE SUPERPOSITION OF TIME FOR TRANSIENT ANALYSIS OF BOTH LINEAR AND RADIAL FLOW. NOTE THAT ONLY FIGURE 4 WILL CHANGE WHEN YOU CHANGE FLOW OPTIONS. DIETZ SHAPE FACTOR ------------------ THE DIETZ SHAPE FACTOR IS AUTOMATICALLY CALCULATED WHEN YOU SELECT TWO POINTS WHICH REPRESENT RADIAL TRANSIENT FLOW, AND TWO POINTS WHICH REPRESENT PSEUDO STEADY STATE FLOW. IF YOU LOOK AT THE DERIVATION OF THE DIETZ SHAPE FACTOR, YOU WILL NOTICE THAT ITS PRIMARY COMPONENTS ARE THE SLOPES AND INTERCEPTS FROM THE POINTS YOU SELECTED FROM BOTH FIGURE 3 (TRANSIENT RADIAL FLOW) AND FIGURE 4 (PSEUDO STEADY STATE FLOW). IN OTHER WORDS, IT CAN SERVE AS A CHECK TO THE POINTS YOU SELECTED FROM BOTH FIGURES 3 AND 4. THE DIETZ SHAPE FACTOR SHOULD BE CLOSE TO 31.62 IF (1) YOU SELECTED THE CORRECT POINTS FROM BOTH FIGURES, AND (2) THE RATES DID NOT VARY SIGNIFICANTLY. TYPICALLY, HOWEVER, THE POINTS ON FIGURE 4 (ESPECIALLY WITH FLOW OPTION 1) WILL DISPLAY PARALLEL LINES WHEN THE RATES VARY. WHEN THIS OCCURS, DO NOT WORRY ABOUT OBTAINING A DIETZ SHAPE FACTOR OF 31.62. THE SLOPE OF THE LINE FOR FIGURE 4 WILL STILL BE CORRECT, AND THE RESERVES-IN-PLACE WILL STILL BE CORRECT. PREPARING FOR THE GAS SIMULATOR ------------------------------- AFTER RUNNING THE DRAWDOWN.EXE MODULE, THEN RUN DDTOGM.EXE TO CREATE AN INPUT FILE FOR THE GASMODEL.EXE MODULE IF THIS IS A GAS WELL OR A GAS/CONDENSATE WELL. IMPROVING RESOLUTION OF PLOTS ----------------------------- IF YOU NEED TO IMPROVE THE RESOLUTION OF THE PLOTS FOR THE EARLY TIME DATA, THEN CHOOSE OPTION 3 AFTER THE PLOT IS DISPLAYED TO THE SCREEN. IT WILL THEN ASK YOU TO SELECT A LETTER WHICH CORRESPONDS TO THE LAST POINT YOU WANT TO PLOT. HOW TO HANDLE GAS WELLS PRODUCING WATER AND/OR CONDENSATE --------------------------------------------------------- IF STARTING WITH DATA FROM A BOTTOM HOLE BOMB, THEN USE THE DDINPUT1.EXE MODULE TO CREATE AN INPUT FILE FOR THE DRAWDOWN ANALYSIS. IF STARTING WITH DAILY GAUGE REPORTS, OR ANY OTHER SURFACE PRESSURE MEASUREMENTS, THEN USE THE DDINPUT2.EXE MODULE TO CREATE AN INPUT FILE FOR THE DRAWDOWN ANALYSIS. THE DDINPUT2.EXE MODULE WILL CALCULATE BOTTOM HOLE FLOWING PRESSURES FROM THE WELLHEAD PRESSURES INCLUDING ADJUSTMENTS FOR CONDENSATE AND/OR WATER PRODUCTION AND THEN PLACE ALL NECESSARY INFORMATION INTO AN INPUT FILE. WHEN PROMPTED "INCLUDE OIL AND WATER?" THEN ANSWER "YES". THEN THE PERMEABILITY AND PROVED ACRES WILL BE FOR THE COMBINED FLUID. IF YOU WANT THE SAME VALUES FOR THE GAS ONLY, THEN YOU CAN MULTIPLY THESE VALUES BY THE RATIO OF CUMULATIVE GAS TO CUMULATIVE EQUIVALENT GAS. HOW TO HANDLE OIL WELLS PRODUCING WATER --------------------------------------- OIL WELLS WHICH PRODUCE WATER SHOULD BE HANDLED IN THE FOLLOWING MANNER. WHEN YOU ARE PROMPTED "INCLUDE WATER?" THEN ANSWER "YES". WHEN YOU ARE PROMPTED FOR BO (FORMATION VOLUME FACTOR), UO (VISCOSITY), AND CO (COMPRESSIBILITY), ENTER WEIGHTED AVERAGE VALUES BASED ON THE PROPORTIONS OF OIL AND WATER FLOWING. THE PERMEABILITY AND PROVED ACRES CALCULATED WILL BE FOR THE COMBINED FLUID. IF YOU WANT THESE SAME VALUES FOR THE OIL ONLY, THEN YOU CAN MULTIPLY THESE VALUES BY THE RATIO OF OIL RATE TO TOTAL FLUID RATE. THE ONLY LIMITATION OF APPLYING THIS METHOD IS THAT THE GAS SATURATION SHOULD BE LESS THAN THE CRITICAL SATURATION FOR FREE GAS FLOW. THE OIL AND WATER COMPRESSIBILITIES CALCULATED BY THE OILPROP.EXE MODULE ASSUME THAT THIS IS THE CASE. HOW TO HANDLE WATER WELLS ------------------------- WHEN YOU ARE PROMPTED "INCLUDE WATER?" THEN ANSWER "YES". WHEN YOU ARE PROMPTED FOR BO (FORMATION VOLUME FACTOR), UO (VISCOSITY), AND CO (COMPRESSIBILITY), ENTER THE FLUID PROPERTIES OF THE PRODUCED WATER. THE PERMEABILITY AND PROVED ACRES CALCULATED WILL NOT NEED TO BE CORRECTED. WELLBORE/FRACTURE STORAGE CORRECTIONS FOR GAS WELLS --------------------------------------------------- DRAWDOWN DATA CAN BE CORRECTED FOR BOTH WELLBORE STORAGE EFFECTS AND FRACTURE STORAGE EFFECTS. THIS WILL ALLOW DATA WHICH IS STILL BEING INFLUENCED BY STORAGE EFFECTS TO BE ANALYZED. THIS IS EXTREMELY USEFUL FOR VERY SHORT DRAWDOWN TESTS SUCH AS AN INITIAL FOUR POINT TEST, OR ANY TEST TYPICALLY LESS THAN ABOUT 24 HOURS. IF YOU ANSWER "YES" TO THE STORAGE QUESTION, THEN YOU WILL NEED TO ENTER THREE ADDITIONAL PIECES OF INFORMATION. IN ORDER TO ESTIMATE THE WELLBORE STORAGE EFFECTS, THE DEPTH OF THE WELL AND THE I.D. OF THE FLOW STRING MUST BE ENTERED. IN ORDER TO ESTIMATE THE EFFECTS OF THE FORMATION FRACTURE STORAGE VOLUME, IT'S SIZE MUST BE ENTERED. IF THE GAS WELL HAS A PACKER, THEN YOU SHOULD ENTER THE I.D. OF THE TUBING. IF THE WELL DOES NOT HAVE A PACKER, THEN YOU SHOULD ENTER AN EQUIVALENT I.D. WHICH ACCOUNTS FOR BOTH TUBING AND ANNULAR VOLUME. NON-DARCY FLOW COEFFICIENT FOR GAS WELLS ---------------------------------------- THE NON-DARCY FLOW COEFFICIENT (F) IS USED TO CORRECT THE FLOW EQUATIONS WHEN NON-DARCY FLOW IS PRESENT. NON-DARCY FLOW IS PRESENT IN HIGH RATE GAS WELLS. IT CREATES AN ADDITIONAL PRESSURE DROP DUE TO TURBULENCE FROM THE HIGH FLOW RATE NEAR THE WELLBORE. THE AMOUNT OF PRESSURE DROP IS PROPORTIONAL TO THE GAS FLOW RATE. TYPICALLY THE NON DARCY FLOW COEFFICIENT IS LESS THAN 0.05 AND CAUTION SHOULD BE USED WHEN USING A VALUE GREATER THAN THIS. FOR THEORETICAL BACKGROUND ON THE NON-DARCY FLOW COEFFICIENT (F) REFER TO THE FOLLOWING REFERENCES: 1. FUNDAMENTALS OF RESERVOIR ENGINEERING, DAKE. 2. THEORY AND PRACTICE OF THE TESTING OF GAS WELLS, ERCB, 1975. 3. PREDICTION OF GAS WELL PERFORMANCE INCLUDING THE EFFECT OF NON-DARCY FLOW, JOURNAL OF PETR. TECH., JULY 1962, PP. 791-798, SWIFT AND KIEL. 4. USE OF OPEN FLOW POTENTIAL TEST DATA IN DETERMINING FORMATION CAPACITY AND SKIN FACTOR, JOURNAL OF PETR. TECH., JULY 1971, PP. 879-887, ESSIS AND THOMAS.