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Why S&mulate? Drilling & Produc&on Problems Solu&ons mud damage well cleanout mud-fluids & mud-solids remove drill-in & completion fluid residu completion fluids lost Optimum connection between reservoir and well Wax, Scale, etc Tubing/wellbore clean out matrix acidizing Remove FormationDamage Deposits clay problems hydraulic fracturing clay swelling, clay & fines migration Increase inflow area low permeability poor productivity Oct-19-15 Productivity Optimization Course day Wellbore Cleanout fines Matrix S&mula&on mudcake Acid ¥ Remove near wellbore formation damage: Ð mud fluids/particles Ð lost completion fluids Ð clay fines, clay swelling _ ft ¥ Common acids: HCl, HCl/HF (clay), Acetic, Formic ¥ Treatment fluids are pumped into formation ¥ Radius affected: 0.1 Ð m (0.3 Ð ft) damage Workflow CandidateSelection Skin Analysis (Ranking table) Job Execution Treatment Selection ¥ Tubing Clean-out ¥ Wellbore Clean-out ¥ Scale Removal ¥ Sandstone Acidizing ¥ Carbonate Acidizing Treatment Advisor Damage Advisor Production Response Evaluation Cycle Skin Prediction Fluid Placement Simulator Fluid Selection Pumping Schedule (Stage #, Volume, Rate) Geochemical Simulator ¥ Pre-flush ¥ Main flush ¥ Post-flush ¥ Diversion Carbonate Sandstone Expert System Diversion Advisor Treatment Evaluation Candidate Selec&on and Matrix Acid S&mula&on Design Forma&on damage – causes and remedia&on ! Candidate Selection ! Problem Identification ! ! Formation Damage Mechanisms Identifying and Diagnosing the Causes of Damage Forma&on damage – causes and remedia&on ! Candidate Selection ! Problem Identification ! Fluid Selection + Types of Acids + Carbonate Acidizing Chemistry + Carbonate Matrix Acidizing Systems + Sandstone Acidizing Chemistry + Sandstone Matrix Acidizing Systems + Acid Additives Forma&on damage – causes and remedia&on ! Candidate Selection ! Problem Identification ! Fluid Selection ! Diversion, Pumping Schedule & Placement + Diversion Methods and Materials + Pumping Schedule Generation + Fluid Placement Simulation Forma&on Damage in Injec&on Wells ! Water is injected into resrvoirs for pressure maintenance, water disposal or water flooding ! Maintaining high injectivities over long periods of time is extremely important for all water injection projects ! Ensuring sustained injectivity of water is determined by: ! Freshwater sensitivity of the formation ! Precipitation of inorganic scale ! The total dissolved solids in the injection water ! The total suspended solids Forma&on Damage in Injec&on Wells ! Ensure that the salinity is above the critical salt concentration for the rock ! The precipitation of inorganic scale is a major concern when injecting water with large concentrations of calcium, magnesium, iron or barium ! Large persistent drops in injectivity are likely when inorganic scales are formednear the injection wells ! The presence of solids and oil droplets in the injection fluid can result in severe and rapid injectivity decline The graph shows the injectivity of a well in the offshore Gulf of Mexico. Despite the relativity good quality of the water, a rapid reduction in injectivity was observed Forma&on Damage in Injec&on Wells ! In the Prudhoe field in Alaska contaminated water has been injected into injection wells with minimal impact on injectivity ! The apparent lack of formation damage is a consequence of thermally induced fractures that can propagate hundred of meters into the formation ! When fracturing injection wells is undesirable, the quality of the injection water plays an important role in determining well injectivity or formation damage ! Various water purification devices such as sedimentation tanks, sand filters, cartridge filters, flotation devices or hydrocyclones are available. These facilities significantly prolong the life of water injection wells Forma5on Damage due to Paraffins and Asphaltenes ! Crude oils contain three main groups of compounds: ! saturated hydrocarbons or paraffins, ! aromatic hydrocarbons and ! resins/asphaltenes ! The table shows the gross composition of crude oils, tars and bitumens obtained from various sources ! More degraded crudes, including tars and bitumens contain substantially larger proportions of resins and asphaltenes Forma5on Damage due to Paraffins ! The primary cause of wax deposition is a loss in solubility in the crude as a result of changes in temperature, pressure or composition of the crude oil (evaporation of gas) ! Reductions in pressure usually lead to loss of volatiles induce the precipitation of paraffins. ! The temperature profile in the near‐wellbore region and tubing controls where the wax will be deposited, with the tubing being more likely ! The injection of cold fluids such as stimulation fluids or injection water into the wellbore can also induce paraffin deposition Asphaltene Precipita5on ! In crude oils asphaltene structures are dispersed and maintained in suspension by the action of resins ! Precipitation of asphaltenes occurs through the formation of aggregates. The solubility of asphaltenes is a function of temperature, pressure and the composition of the crude oil ! When the reservoir gets depleted and the bubble point pressure is achieved lower in the tubing or even in the formation itself, asphaltene deposition may occur at those points ! Asphaltene deposition can also be induced by changes in composition in the crude oil through injection of fluids such as CO2 or lean gas Forma5on Damage due to Emulsion and Sludge Forma5on ! Crude oil and brine/formation water emulsions are stabilized by the presence of natural surfactants and clay fines, wax and asphaltenes ! Emulsions are hard to remove; prevention the formation of emulsions is critical ! Mutual solvents and surfactants (demulsifiers) are the most common way of trying to remove emulsions from the near wellbore region ! However placing the treatment fluids in the obstructed zones can be cumbersome Forma5on Damage due to Condensate Banking ! The buildup of a condensate bank in gas well van cause a loss in PI by a factor of 2 to 8 ! Hydraulic fracture stimulation is the most common method used to remedy condensate build up problems ! The fracture results in a significant decrease in the drawdown needed to produce the well. ! In addition, the build up of a liquid hydrocarbon phase on the faces of the fracture has a limited impact the well ! Recently, the use of solvents and surfactants such as methanol can also stimulate gas condensate wells Forma5on Damage due to Gas Breakout ! In solution gas drive reservoirs as the reservoir fluid pressure drops below the bubble point a gas phase is formed ! If the bubble point is reached in the near wellbore region, a significant gas saturation builds up around the wellbore resulting in a decrease in the oil relative permeability ! This type of damage is easy to establish but requires phase behavior data ! A common method to remedy this to allow a reduction drawdown by hydraulically fracturing the well Forma5on Damage due to Water Blocks ! If large volumes of water‐based drilling or completion fluids are lost to a well it results in a formation of a region of high water saturation around the wellbore ! In this region the relative permeability to the hydrocarbon phases is decreased resulting in a net loss in well productivity. ! Regions of high water saturation, or water blocks around the wellbore, are expected to dissipate with time as the hydrocarbon fluids are produced. ! Water blocks will generally be more troublesome for low permeability, depleted gas wells Forma5on Damage due to Weφability Altera5on ! Converting a rock from a water‐wet to oil‐wet results in a reduction in the relative permeability hydrocarbons ! The loss of surfactants in drilling and completion fluids, corrosion inhibitors and dispersants in stimulation fluids and the use of resins for sand control can all cause changes in wettability in the near wellbore region ! Treatment with solvents and water wetting surfactants are recommended when oil‐wetting surfactants have been lost to the formation (e.g. by using oil‐based muds) Bacteria Plugging ! Anaerobic bacteria are often present in and around oil and gas wells ! Injection of water‐based fluids can stimulate the growth of bacteria leading to a decline in productivity/injectivity ! The growth of sulfate reducing bacteria can also result in the generation of hydrogen sulfide gas and the fouling of flow lines and facilities. ! The use of a bactericide (such as sodium hypochlorite) is sometimes an effective but expensive method to tackle this problem. Summary ! We have discussed methods to measure and quantify formation damage in oil and gas wells ! Several different mechanisms responsible for causing formation damage were discussed ! Some methods to remove the damage were also discussed ! Most of the time acidizing is an effective method of removing the damage ! Sometimes acidizing is not effective ! It is, therefore, very important to correctly identify the damage mechanism before stimulating a well Problem Identification Treatment Op&ons ‐ Dependent on Damage Type Cause of damageDamage type Treatment (Mud) Acid treatment Solids invasion Drilling, completion, etc Specific well treatment* Chemical interaction *Stimulation, gravel packing (re-)perforation, etc Precipitates, Clay swelling Mud Acid treatment Emulsions Solvent/ surfactant treatment Wax, asphaltenes Solvent/ surfactant treatment Formation fines Acid treatment Precipitates, scale Acid treatment Clay swelling Mud Acid treatment Oily/inhibitor residues Solvent/ surfactant treatment Produced fluids Water Injected fluids Gas Treatment selec5on Chart Problem Solution Damage from water based muds Acidising Damage from oil based muds Acidising + (mutual) solvents Completion and Workover Fluids Acidising Damage during Cementing Acidising Damage during Perforating Acidising (HF) Fines Migration Acidising (HF) Swelling Clays Acidising (HF) Formation Damage in Injection Wells Acidising Paraffins Aliphatic solvents – e.g. Kerosene Asphaltene Precipitation Aromatic solvents Emulsion and Sludge Formation (Mutual) Solvents and surfactants Condensate Banking Hydraulic fraccing, Methanol injection Gas Breakout Hydraulic fraccing Water Blocks Swabbing, (mutual) solvents+ surfactants Wettability Alteration (Mutual) solvents+surfactants Bacteria Plugging Hypochlorite (bleach) ... 10 16 ,875 1 1 10 10 20 10 0 10 9,2 8 10 10 10 8 ,15 10 0 10 40 ,14 ‐4 1 10 10 2 10 0 10 16 , 015 ‐7 1 10 10 10 ,5 10 0 10 25,75 9 10 10 10 20, 21 10 10 11 ,6 ... 11 ,6 9 10 10 10 21, 97 10 10 0 9 10 10 10 23 , 13 10 10 4 ,19 5 9 10 10 10 12 ,89 10 10 36 ,885 6 10 10 10 ‐0,6 10 10 22,67 2 10 10 10 8 ,1 10 10 6,625 9 10 ... 10 10 10 10 ,3 10 10 10 ,505 9 10 10 10 3, 54 10 10 3 ,18 9 10 10 10 5 ,35 10 10 0 9 10 10 10 5,24 10 10 12 ,66 ‐8 10 10 10 0,24 10 10 9,86 ‐26 10 10 10