NATIONAL CONFERENCE ON HYDROCARBON RESERVOIR ENGINEERING, SCIENCE AND RELATED INDUSTRIES | Year:2012 | دوره:1 |Papers Count:8

TWO COMMONLY-USED EOR METHODS IN THE IRANIAN RESERVOIRS ARE WATERFLOODING AND GAS INJECTION. EARLY BREAKTHROUGH OF THE INJECTED FLUID IN THE PRODUCTION WELLS IS THE MAJOR PROBLEM ASSOCIATED WITH THESE PROCESSES. A SOLUTION TO THIS PROBLEM IS AN ALTERNATIVE PROCESS CALLED WATER-ALTERNATING-GAS (WAG). IN RECENT YEARS THERE HAS BEEN AN INCREASING INTEREST IN WAG PROCESSES, BOTH MISCIBLE AND IMMISCIBLE. MANY OF THE IRANIAN FRACTURED RESERVOIRS ARE LOCATED IN THE INCLINED RESERVOIRS. SO, WAG INJECTION COULD INCREASE THE RECOVERY BY CONTACTING THE UPSWEPT ZONES, ESPECIALLY RECOVERY OF ATTIC OR CELLAR OIL BY EXPLOITING THE SEGREGATION OF GAS TO THE TOP OR ACCUMULATING OF WATER TOWARDS THE BOTTOM. THE WAG PROCESS HAS BEEN PROVED BENEFICIAL IN RE-PRESSURIZING THE RESERVOIR WHEN COMPARED TO A WATERFLOOD ONLY PROCESS. THIS HIGHER PRESSURE IS CAUSED BY THE GAS SLUG BEING INJECTED AT AN EXTREMELY HIGH VOIDAGE REPLACEMENT RATE BECAUSE OF ITS HIGH MOBILITY. WAG INJECTION INCREASES THE EFFICIENCY OF THE PLAIN GAS INJECTION, TOO. BY ALTERNATING THE GAS INJECTION WITH WATER INJECTION, THE GAS RELATIVE MOBILITY IN THE RESERVOIR IS REDUCED OVER GAS INJECTION ONLY. THEREFORE, LESS GAS BREAKS THROUGH TO PRODUCING WELLS, REDUCING GAS HANDLING REQUIREMENTS. FURTHERMORE, THE LOWER PRODUCING GOR ASSOCIATED WITH WAG INJECTION OVER STRAIGHT GAS INJECTION RESULTS IN LESS EROSION OF THE PRODUCTION EQUIPMENT.

IN ANY COMPREHENSIVE RESERVOIR STUDY THE FIRST STEP IS AN ACCURATE ASSESSMENT OF THE SPATIAL DISTRIBUTION OF THE FLUID COMPONENTS IN BOTH HORIZONTAL AND VERTICAL DIRECTIONS. COMPOSITIONAL GRADING, WHICH REFERS TO VARIATION IN FLUID COMPOSITION WITH DEPTH, HAS BEEN OBSERVED IN MANY RESERVOIRS. IN MOST CASES, THE OIL DENSITY AND HEAVY COMPONENTS COMPOSITION INCREASE WITH DEPTH WHILE METHANE AND OTHER LIGHT COMPONENTS COMPOSITION DECREASE WITH DEPTH. SUCH A COMPOSITIONAL GRADING CAN HAVE A SIGNIFICANT INFLUENCE ON VARIOUS ASPECTS OF RESERVOIR DEVELOPMENT. WHEN CONSIDERING GAS INJECTION, ONE MUST BE AWARE THAT COMPOSITIONAL EFFECTS (SUCH AS THE DEVELOPMENT OF MISCIBILITY) CHANGE WITH DEPTH. ALTHOUGH THERE ARE NUMEROUS STUDIES ABOUT COMPOSITIONAL GRADING AND ALL AUTHORS EMPHASIZED THAT VARIATION OF COMPOSITION MAKES VARIATION OF MISCIBILITY CONDITION, BUT ALL OF THEM TRY TO FORMULATE THIS PHENOMENON BASED ON THE THERMODYNAMIC APPROACH TO REACH TO A PROPER MODEL IN ORDER TO PREDICT COMPOSITION AND OTHER RESERVOIR FLUID PROPERTIES ALONG THE RESERVOIR COLUMN, AND THERE IS A LACK OF ATTENTION TO ITS EFFECTS ON GAS INJECTION. IN THIS WORK ONE OF THE SOUTHWEST IRANIAN OIL RESERVOIRS WAS SELECTED. THE RESERVOIR UNDER STUDY WAS A LOW SHRINKAGE UNDER SATURATED OIL RESERVOIR WITH THE OIL API GRAVITY OF 30. TWO SIMULATION MODELS OF CO2 INJECTION FOR ENHANCED OIL RECOVERY (EOR) PROCESS WERE PREPARED, ONE WITH CONSIDERING COMPOSITIONAL GRADING, AND THE OTHER FOR UNIFORM FLUID CONDITION. TWO MODELS WERE COMPARED AND THE EFFECT OF COMPOSITIONAL GRADING ON OPTIMUM INJECTION RATE AND RECOVERY FACTOR WAS STUDIED. CONSIDERING COMPOSITIONAL GRADING RESULTS IN A MORE REALISTIC BUT MORE COMPLEX SIMULATION MODEL, AND SIMULATION RUN TIME WOULD INCREASE, BUT BECAUSE OF THE DRASTIC DIFFERENCE BETWEEN THE RESULTS OF THE TWO CASES, IT CANNOT BE IGNORED.

IN RECENT YEARS THERE HAS BEEN AN INCREASING INTEREST IN WAG PROCESSES, BOTH MISCIBLE AND IMMISCIBLE. DESIGN OF WAG PROCESS IS MORE COMPLICATED THAN WATERFLOOD AND GAS INJECTION PROCESSES, DUE TO EXISTENCE OF THREE MOBILE PHASES SIMULATANEOUSLY. PARAMETERS THAT SHOULD BE CONSIDERED FOR THE WAG PROCESS INCLUDE RESERVOIR HETEROGENEITY AND STRATIFICATION, ROCK AND FLUID CHARACTERISTICS, INJECTION GAS CHARACTERISTICS, INJECTION PATTERN, TAPERING (CHANGE IN WATER TO GAS RATIO THROUGHOUT THE FLOOD), WAG INJECTION PARAMETERS (WATER TO GAS RATIO, NUMBER OF CYCLES, INJECTION RATES), FLOW DISPERSION EFFECTS (RELATIVE PERMEABILITY DESCRIPTION FOR THREE PHASES), GRAVITY CONSIDERATIONS IN WAG AND LABORATORY STUDIES AND SIMULATION. PLAIN GAS INJECTION IS A WAG PROCESS WITH WATER TO GAS RATIO OF 0:1, HENCE THESE THESE DESIGN ISSUES ARE APPLICABLE TO GAS INJECTION DESIGN. THE POPULARITY OF THE WAG PROCESS IS EVIDENT FROM THE INCREASING NUMBER OF PROJECTS AND MANY SUCCESSFUL FIELD WIDE APPLICATIONS. WATERFLOODING AND PLAIN GAS INJECTION ARE TWO COMMONLY-USED EOR METHODS IN IRANIAN RESERVOIRS, BUT THEIR ASSOCCIATED PROBLEMS LEAD TO LOWER PRODUCTION LIFE OF THE WELLS. IT'S BEEN APPROVED THAT WAG PROCESS, IN SOME CASES, MODIFIES THE DEMERITS OF THESE PROCESSES, HENCE MORE RESIDUAL OIL IS PRODUCED. AFTER DESIGN OF THE WAG PROCESS PILOT TESTS ARE REQUIRED TO MONITOR ITS PERFORMANCE IN THE FIELD.

A NATURALLY FRACTURED RESERVOIR MAY BE DIVIDED VERTICALLY INTO SEVERAL ZONES, I.E. GAS CAP, GAS INVADED, UNDER SATURATED OIL, WATER INVADED, AND AQUIFER. GRAVITY DRAINAGE IS THE MAIN OIL PRODUCING MECHANISM IN GAS INVADED ZONE. DEPENDING ON THE WETTABILITY OF THE RESERVOIR ROCK, THE MAIN RECOVERY MECHANISM IN WATER INVADED ZONE WILL BE GRAVITY DRAINAGE OR IMBIBITION FOR OIL WET OR WATER WET ROCK, RESPECTIVELY. WHEN PRODUCTION FROM A RESERVOIR STARTS AFTER A WHILE, THE PRODUCTION WILL DECREASE BECAUSE OF RESERVOIR DEPLETION. TO ENHANCE THE FINAL RECOVERY THERE ARE SOME SCENARIOS, ONE OF THEM IS WATER INJECTION. WATER INJECTION HAS BEEN THE MOST USED RECOVERY METHOD IN PETROLEUM INDUSTRIES DUE TO ITS ADVANTAGES. THE INJECTED WATER DISPLACES OIL FROM POROUS MEDIA TO PRODUCING WELLS AND MAINTAINS THE RESERVOIR PRESSURE ABOVE OF SATURATION PRESSURE, INCREASING THE RECOVERY PROCESS EFFICIENTLY. ONE OF IMPORTANT VARIABLE IS INJECTION RATE THAT INFLUENCE THE WATER INJECTION PERFORMANCE, THEREFORE BY SIMULATING THE RESERVOIR WITH DIFFERENT INJECTION RATE WE COULD OBTAIN THE PROPER ONE FOR RESERVOIR DEVELOPMENT.THE GOAL OF THIS WORK IS TO STUDY THE IMPACT OF WATER INJECTION RATE ON THE RESERVOIR PERFORMANCE AND SIMULATE THE WATER INJECTION PERFORMANCE IN RESERVOIR SCALE. THIS WORK IS A CASE STUDY ON AZADEGAN OIL RESERVOIR.THIS WORK IS DONE ON INVESTIGATION OF WATER INJECTION IN SECTOR A OF AZADEGAN OIL RESERVOIR THAT IT HAS A DUAL POROSITY MANNER. WATER INJECTION SIMULATIONS WERE PERFORMED AT DIFFERENT RATES. BEFORE ANY INJECTIONS THE PLATEAU TIME IS ABOUT 5000 DAYS. AFTER PUTTING THE INJECTION WELLS AND APPLIES THE RATES IT IS OBSERVED THAT THE PLATEAU TIME IS INCREASED. HIGHER WATER INJECTION RATES RESULTS IN HIGHER OIL PRODUCTION SO WATER INJECTION IS SUITABLE FOR THIS DUAL POROSITY CASE. BECAUSE WATER MOVES THROUGH FRACTURES QUICKLY AND SO CAPILLARY IMBIBITION PROCESS CAN HELP PUSH THE OIL TO PRODUCING WELL.

RE-INJECTION OF PRODUCED WATER IS OF INCREASING IMPORTANCE AS WATER CUTS CONTINUE TO INCREASE WORLDWIDE. IT PROVIDES AN ENVIRONMENTALLY ACCEPTABLE SOLUTION TO THE DISPOSAL OF PRODUCED WATER, AND CONTRIBUTES TO PRESSURE MAINTENANCE WHEN INJECTION TAKES PLACE IN THE RESERVOIR ITSELF. INJECTION CAN TAKE PLACE UNDER MATRIX INJECTION OR FRACTURING CONDITIONS. IN BOTH CASES, THE PERFORMANCE OF THE INJECTION WELL AND THE DISTRIBUTION OF THE INJECTED WATER ARE STRONGLY INFLUENCEDBY THE BUILD-UP OF FORMATION IMPAIRMENT AROUND THE WELLBORE OR THE FRACTURE FACE. SOLID PARTICLES AND SMALL OIL DROPLETS DISPERSED IN THE INJECTION WATER ARE DEPOSITED IN THE FORMATION BY A PROCESS OF FILTRATION, AND THEREFORE WILL CAUSE THIS IMPAIRMENT. THIS PAPER PRESENTS RESULTS FROM AN EXPERIMENTAL STUDY ON FORMATION DAMAGE ASSOCIATED WITH SIMULATED PRODUCED OILY WATER INJECTION. CORE FLOODING EXPERIMENTS WERE CARRIED OUT WITH SIMULATED PRODUCED OILY WATER CONTAINING 200 TO 1200 PPM CRUDE OIL AND 600-1500 PPM SOLIDS (10 MMMEAN DIAMETER) DISPERSED IN BRINE. THE FORMATION DAMAGE ALONG THE LENGTH OF A CORE WAS INVESTIGATED AND A NUMBER OF PARAMETERS CONTRIBUTING TO PERMEABILITY DECLINE WERE EVALUATED. THE RESULTS INDICATE THAT PRODUCED OILY WATER CONTAINING OIL DROPLETS AND SOLID PARTICLES CAN CONTRIBUTE TO THE PERMEABILITY DECLINE OBSERVED IN THE CORES. THE MOST SEVERE DECLINE OCCURRED IN THE LOW FLOW RATE OF OILY WATER INJECTION AND PERMEABILITY DECLINES ARE DECREASED BY INCREASING INJECTION FLOW RATE. OILDROPLETS WITH A DIMENSION SIGNIFICANTLY LESS THAN THE PORE THROAT DIAMETER ALSO LED TO PERMEABILITY DECLINE. THE PERMEABILITY ALTERATION RESULTING FROM A COMBINATION OF BOTH OIL DROPLETS AND SOLID PARTICLES IS MORE SEVERE THAN OBTAINED FROM THE SYSTEMS INDIVIDUALLY.

TODAY WITH THE ADVANCES IN SCIENTIFIC ABILITIES IN PREDICTING THE CONTROLLABLE FACTORS IN OPTIMIZING AND SUCCESS OF INDUSTRIAL PROJECTS, THE NEED TO MAKE A FUTURE WITH SIMULATION AND PROGRAMMING IN THE CURRENT IMPORTANT AND INFLUENTIAL INDUSTRY IN WORLD FINANCE IS INEVITABLY FELT.WITH THE INTRODUCTION OF THE RELATED SIMULATIONS AND SOFTWARE IN OIL INDUSTRY, IT BECOMES UTTERLY IMPORTANT TO HAVE PRECISE INFORMATION ABOUT WHAT WILL HAPPEN BEFORE THE DIGGING PROCESS INCLUDING THE DIGGING ITSELF, PRODUCTION AND RESERVOIR SIMULATION.IN THIS ARTICLE, PREDICTION OF THE PHYSICAL SHAPE OF THE RESERVOIR, NAMED DRAINAGE AREA, IS DISCUSSED. KNOWING ABOUT THE RADIUS OF INVESTIGATION IN WELLS WE CAN FIND OUT USEFUL INFORMATION REGARDING THE BOUNDARIES, DISTRIBUTION OF PRESSURE IN BOUNDARIES AND THE WAY OF DIRECT USAGE OF THE BASIC SIMULATION CALCULATION EQUATION.THE HISTORY OF INVESTIGATING THIS PARAMETER GOES BACK TO 1960S. WITH THE COMPLEMENTARY EFFORTS OF DIETZ A TABLE WAS FOUND FOR THE SHAPE OF THE RESERVOIRS. HOWEVER, BASED ON THE NEEDS OF THE PERSIAN GULF COUNTRIES THAT OUR OIL RESERVOIRS ARE PLACED IN FORMATIONS WITH NATURAL FRACTURE, CALCULATING THIS PARAMETER IN THIS RESERVOIR WITH THE USE OF THAT TABLE WAS WRONG AND WILL RESULT IN UNRELIABLE ANSWER.THEREFORE, WE NEED TO CALCULATE THIS PARAMETER FOR FRACTURED RESERVOIRS.GENERALLY, IN FUNDAMENTAL EQUATION IN RESERVOIR ENGINEERING, TWO PARAMETERS OF CA AND A NAMED SHAPE FACTORS AND DRAINAGE AREA, ENTERED THE EQUATION SIMULTANEOUSLY OR THE EQUATION ARE DEFINED BASED ON RE PARAMETER THAT GIVES US THE WRONG UNDERSTANDING OF THE BOUNDARIES OF THE RESERVOIRS WITH THE SIMPLIFICATION OF A CYLINDER.IT WORTH NOTICING THAT THE INVESTIGATION OF DRAINAGE IS POSSIBLE ONLY IF THE SHAPE OF THE RESERVOIR IS FOUND. THE METHOD OF FINDING CA IS USING CONTINUOUS EQUATION OF IMAGE WELLS THAT WILL NOT BE INVESTIGATED IN THIS ARTICLE.FEW STUDIES WERE DONE ON INVESTIGATING A AND CA IN NFR. HOWEVER, THE SHORTCOMING OF ALL THESE ARTICLES IS USING PURE MATHEMATICAL METHODS AND TRANSPORTING FUNCTIONS FOR FORMING FUNDAMENTAL EQUATION OR USING CONVERGING RESERVOIR METHOD FOR THE NFRS.THE PURPOSE OF THIS ARTICLE IS CALCULATING A AND CA WITH THE HELP OF PHYSICAL MODELS AND USING REGULAR EXPERIMENTS ON WELLS TO FIND A AND CA. WE USE IPR CURVE AND WELL TEST IN PARALLEL.

ONE OF THE MOST SERIOUS PROBLEMS IN THE WATER INJECTION PROCESS IS SCALE FORMATION OCCURRENCE WHEN INJECTION WATER IS INCOMPATIBLE WITH FORMATION BRINE. THESE TWO WATERS INTERACT CHEMICALLY AND PRECIPITATE INORGANIC MINERALS. FOR EXAMPLE SEAWATER WITH HIGH CONCENTRATION OF SULFATE IONS AS INJECTION WATER REACHES TO FORMATION WATER WITH CATIONIC IONS. THE PURPOSE OF THIS STUDY IS TO PREDICT THE PERMEABILITY REDUCTION CAUSED BY DEPOSITION OF SCALES IN SANDSTONE CORES FROM MIXING OF INJECTED SEA WATER AND HIGH SALINITY FORMATION WATER AT VARIOUS TEMPERATURES (60-100OC) AND DIFFERENTIAL PRESSURES (50-150 PSIG). A VERY COMMON WAY TO PREDICT THE SCALE FORMATION IS RUNNING CORE FLOOD EXPERIMENTS IN A WAY THAT FIRST, THE CORE WAS SATURATED WITH FORMATION BRINE AND SET TO DESIRED TEMPERATURE THEN SEA WATER WAS INJECTED AT A CONSTANT PRESSURE AND CONTINUOUSLY BY MEASURING FLOW RATE THE PERMEABILITY WAS RECORDED WITH TIME. BUT SEVERAL FACTORS LIKE PARTICLE MOVEMENT, CLAY SWELLING AND PORE THROAT BLOCKING BY FINES MIGRATION CAN DISTURB FLOODING TEST RESULTS AND MAKE DOUBT IN PREDICTIONS. AS A NEW METHOD BY MEASURING THE ELECTRICAL CONDUCTIVITY OF OUTLET WATER THE SCALE FORMATION WAS PREDICTED INDEPENDENT OF NON-RELATED PARAMETERS MENTIONED ABOVE. ELECTRICAL CONDUCTIVITY OF OUTLET WATER DROPPED OUT OF THE RANGE BETWEEN INJECTION AND FORMATION WATER ELECTRICAL CONDUCTIVITIES, SO IT SHOWS A DECREASE IN FREE ION CONCENTRATION IN MIXED WATERS AS A RESULT OF SCALE FORMATION AND PRECIPITATION IN CORE. THE RESULTS SHOWED THAT CALCIUM, STRONTIUM, AND BARIUM SULFATES ARE FORMED AND CAUSE PERMEABILITY DAMAGE. CASO4 AND SRSO4 SCALES WILL DEPOSIT MORE IN HIGHER TEMPERATURES BUT BASO4 SCALE DEPOSIT LESS. AT HIGHER PRESSURES ALL OF THEM PRECIPITATE MORE.

EMPIRICAL METHODS ARE BASED ON DIRECT OBSERVATION, MEASUREMENT AND EXTENSIVE DATA RECORDS. MECHANISTIC MODELS ARE BASED ON AN UNDERSTANDING OF THE BEHAVIOR OF A SYSTEM'S COMPONENTS. FOR EXAMPLE, YOU CAN OBSERVE THE CHANGE OF THE TIDES OVER MANY YEARS, AND CONSTRUCT AN EMPIRICAL MODEL THAT ALLOWS YOU TO PREDICT WHEN TIDES WILL OCCUR, WITH NO UNDERSTANDING OF HOW THE EARTH, MOON AND SUN INTERACT. YOU CAN ALSO CREATE A MATHEMATICAL, MECHANISTIC MODEL THAT USES THE LAWS OF PHYSICS TO PREDICT TIDES.