188bet asia ORGANIC AND INORGANIC FORMATION DAMAGE AND REMEDIATION
Summary
Organic and inorganic skin damage in oil producing wells is a major factor in 188bet asia loss of productivity and revenue. Paraffin, asphaltene, scale deposition and emulsions in 188bet asia formation and around 188bet asia wellbore create a barrier for 188bet asia transportation of crude oil through 188bet asia formation to 188bet asia tubing. Many producing wells have experienced a production decline that cannot be explained by reservoir depletion. Organic and inorganic damage may occur naturally or through various intervention practices used in 188bet asia oilfield. An increased awareness of 188bet asia potential for ongoing damage has been developing slowly over time. Better methods of problem identification, programs to remediate these problems and stimulation software have been developed in recent years. 188bet asia paper discusses potential sources of organic and inorganic damage, problem identification test techniques, stimulation software, chemical selection and applications. A number of brief case histories are presented as examples.
Key words: Organic, inorganic, paraffin damage.
1. Introduction
Skin damage in a producing well is a combination of contributing factors from two general groups. 188bet asia sources for organic deposition are comprised primarily of paraffin and asphaltene deposition. 188bet asia sources for inorganic damage are various scale deposits, sand, silt and clay migration.
188bet asia organic sources are naturally occurring components of crude oil. Paraffins are composed of only carbon and hydrogen atoms with a carbon chain length starting at C18-20 up to C70 or higher. Though paraffins are usually straight-chained hydrocarbons, they can also contain a variety of branched alkyl or cyclic groups. Asphaltenes are heterocyclic unsaturated macromolecules consisting primarily of carbon, hydrogen, and minor components such as sulfur, oxygen, nitrogen and various heavy metals. These higher molecular weight components of crude oil are in equilibrium at “normal” reservoir condition. As crude oil is produced this equilibrium is upset by a number of factors such as temperature declines, pressure reductions, addition of miscible gases and liquids, acidising, hot oiling and other oilfield operations. 188bet asia primary mechanism for paraffin deposition is thermal cooling. Decreases in temperature promote paraffin deposition. 188bet asia key mechanisms for asphaltene deposition are 188bet asia decrease in pressure and 188bet asia introduction of incompatible fluids [1 - 3].
188bet asia inorganic sources are naturally occurring components in 188bet asia produced water or from 188bet asia formation matrix. Scale deposits are composed of a variety of inorganic compounds, but most commonly calcium carbonate, barium sulfate and calcium sulfate. These scale deposits can form under natural production conditions or as 188bet asia result of mixing incompatible water sources. Incompatible water sources can be 188bet asia result of production from multiple formations, water flooding or water based fluids injected into 188bet asia well for a variety of well related activities such as fracturing, salt block removal, and well killing, etc. A variety of formation material consisting of sand, silt and clay can migrate through 188bet asia formation and plug pore throats to impact production. These particles can become oil-wet and agglomerate into larger masses creating even greater plugging potential. All these sources of potential damage migrate and accumulate in 188bet asia near wellbore regions. All 188bet asia well production fluids and gas have to be squeezed through an ever decreasing smaller number of pores as they approach 188bet asia wellbore. This leads to a buildup of skin over time and 188bet asia resulting decrease in 188bet asia potential productivity of 188bet asia well.
2. Problem identification
In order to solve 188bet asia damage problem in 188bet asia most cost efficient manner, it is necessary to identify 188bet asia primary source of 188bet asia damaging mechanism in a particular well. First, one would want to gather as much information on 188bet asia particular well in question as possible through a systems analysis. This information would consist of production history, current production rates of oil, gas and water, drive type, well depth, temperature and pressure profile, well configuration, fluid level, enhanced oil recovery technique, stimulation and maintenance history.
Secondly, a series of laboratory testing on samples of crude oil, water and solid deposits would be conducted to characterise these fluids. 188bet asia crude oil is characterised by wet chemical and instrumental analysis for % paraffin,
% asphaltenes, % asphaltic resins, % aromatic and % saturates. A cloud point, pour point, gas chromatograph and viscosity profile is also run. Water samples would be tested using ICP for elemental analysis and 188bet asia scaling index calculated using any of a variety of scale modelling softwares to determine 188bet asia scaling tendencies. Solid deposits would be characterised through wet extraction methods, Fourier transform-infrared spectroscopy (FTIR), high-temperature gas chromatography (HTGC), x-ray diffraction (XRD) and x-ray fluorescence (XRF) for compositional information.
A series of selected specialised deposition/instability tests is run to investigate 188bet asia potential for deposition from 188bet asia various samples. For paraffinic crudes these consist of paraffin deposition tests using cold fingers or other thermal deposition devices. 188bet asia potential for asphaltene deposition is studied by conducting depressurisation studies on live oils to determine 188bet asia asphaltene flocculation point. For surface samples of crude oil a variety of asphaltene instability tests are conducted. These consist of flocculation point determinations using a variety of anti-solvent titration and measurement techniques such as APDU, Turbiscan and ACSAA (Analytical Centrifuge Stability Analysis for Asphaltenes). From 188bet asia information gathered using these various tests, 188bet asia source and magnitude of 188bet asia problem can be identified. Primary, secondary and even tertiary problem sources can be identified as drivers for formation damage.
A third step in 188bet asia process is an analysis of 188bet asia well production history gathered in step one. Generally, a target candidate will have a production decline which is much higher than 188bet asia field average. Candidate wells can have fluid build-up studies conducted to eliminate reservoir depletion as 188bet asia possible source of production decline. This also establishes a baseline of damage for future review. Often, fluid build-up studies are not available or deemed to be too costly to conduct on marginal wells. In this instance it is necessary to use 188bet asia production history as 188bet asia primary method of candidate well selection. 188bet asia complexity of 188bet asia well configuration and formations to be treated should also be considered. 188bet asia physical location of 188bet asia well, size of perforated interval, number of zones and completion type are just a few of 188bet asia parameters to consider during 188bet asia candidate selection. Less complicated wells will have lower over-all treatment costs. Ideal candidates for treatment and rapid payback are single zone completions with small-perforated intervals. These wells require a minimum amount of equipment and are 188bet asia easiest and 188bet asia least expensive to treat. For these treatments 188bet asia chemical cost may represent 80 - 90% of 188bet asia job cost. At 188bet asia other end of 188bet asia spectrum would be horizontal wells with very long offsets or any deepwater subsea wells. These require a substantial amount of equipment to perform 188bet asia job. This adds additional cost and potentially reduces 188bet asia chemical component cost to about 10 - 20% of 188bet asia total job cost. Each well’s economic analysis needs to take these factors into consideration when evaluating 188bet asia potential for success of 188bet asia job.
3. Laboratory testing
Analysis and testing of crude oil samples is of critical importance for identifying 188bet asia potential source of 188bet asia organic damage. 188bet asia potential for paraffin deposition organic damage is determined by running a number of tests. 188bet asia cloud point (wax appearance temperature) of 188bet asia crude oil is determined using a cross-polarised microscope. A cooling rate of 1°F per minute is typically used, although this is sometime reduced to as low as 0.1°F per minute for special cases. High temperature gas chromatography (HTGC) provides information on 188bet asia % paraffin and carbon number distribution of 188bet asia paraffin wax. Particular attention is focused on 188bet asia amount of paraffin with carbon numbers in excess of 50 which have very low solubility in 188bet asia oil and corresponding high melting points. Often HTGC runs on crude oil samples will indicate no paraffin waxes above C44 because 188bet asia amount of wax present falls below 188bet asia detection limits of 188bet asia equipment. Paraffin waxes in crude oil samples can be concentrated by wet chemical analysis methods to enhance 188bet asia response level of 188bet asia high carbon chain length waxes in 188bet asia oil. Concentrating 188bet asia paraffins can provide indications of paraffin up to or above C70 in those same oils.
188bet asia temperature profile of 188bet asia system is examined to determine if 188bet asia cooling from gas expansion could promote localised paraffin deposition in 188bet asia formation around 188bet asia well bore. A heat transfer software package is used to make these calculations. 188bet asia history of 188bet asia well is also reviewed for evidence of hot oil treatments to control tubular paraffin deposition. A history of hot oiling down 188bet asia casing and particularly down 188bet asia tubing is a good indicator of paraffin damage. This is particularly true if 188bet asia bottom hole temperature is within 30°F of 188bet asia crude oil’s cloud point. 188bet asia actual cloud point of crude oil used for hot oiling down 188bet asia casing has been shown to be in excess of 30°F higher than 188bet asia normal cloud point in previous field investigations. Paraffin damage from hot oil or water down 188bet asia tubing can be substantially greater where even higher molecular weight and melting point wax tubing deposits are pushed into 188bet asia formation.
Paraffin deposition problems are verified in 188bet asia laboratory by running cold finger studies on 188bet asia crude. 188bet asia crude oil is held at a temperature 5°F above 188bet asia cloud point and a cooled probe is inserted into 188bet asia oil. 188bet asia temperature of 188bet asia cooled probe is held at a predetermined level. This is usually 10 to 20°F below 188bet asia oil temperature. 188bet asia test is normally run for a period of 16 - 24 hours. 188bet asia probes are then removed and 188bet asia deposits removed from 188bet asia probes and analysed for paraffin content and gravimetric weight. A wide variety of cold finger designs as well as other pipe loop configurations are used to study paraffin deposition.
188bet asia potential for asphaltene deposition damage is assessed by conducting a SARA (saturates, aromatics, resins, asphaltenes) whole oil analysis. A CII (colloidal instability index) is calculated using 188bet asia following equation:
A historical database was developed over years of fluid’s analysis and correlated to field related problems to develop 188bet asia critical value for 188bet asia CII. For ratios of 0.9 or above, 188bet asia crude oil has been shown to be unstable and asphaltene deposition problems are evident in 188bet asia field. [4].
This instability can be observed in 188bet asia laboratory by titratingtheoilwithavarietyoflinearhydrocarbonsolvents. This test is referred to as 188bet asia APDU test. Typically, hexane, heptane or cetane is used to titrate 188bet asia crude oil to view 188bet asia on-set of asphaltene flocculation and precipitation. Different values are obtained for each solvent used, but these can be standardised to achieve relative stability numbers for each crude oil. 188bet asia Turbiscan test method is similar to 188bet asia APDU in that instability is measured, but generally 188bet asia ratio of dilution solvent is much higher and 188bet asia speed of asphaltene precipitation is measured and recorded over a fifteen-minute period. 188bet asia Baker Hughes ACSAA test method is similar to 188bet asia Turbiscan method, but uses a variety of test solvent solutions, higher oil ratios and adds 188bet asia benefit of centrifugal force to enhance 188bet asia measurement method [5].
If a live-oil sample is available then it would be possible to run a de-pressurisation study on 188bet asia crude oil to identify 188bet asia asphaltene onset precipitation (AOP) as a function of pressure. This would indicate 188bet asia operating pressure range where asphaltene deposition would be possible. De-pressurisation studies on live-oil samples indicate 188bet asia AOP pressure can be thousands of psi higher than 188bet asia bubble point of 188bet asia crude oil. This effectively broadens 188bet asia area of concern for asphaltene organic damage in many systems.
For remediation of asphaltenes, it is generally best to perform chemical evaluation on a solid asphaltene sample from 188bet asia field. With a solid asphaltene sample, a series of dissolution tests can be run with various additives to determine which is best for removal. If a solid sample is not available then dead oil samples are employed to determine 188bet asia most effective chemical. Asphaltenes can be adsorbed onto various formation materials through 188bet asia use of cores or packed columns to determine which additives are 188bet asia best for removal of 188bet asia adsorbed asphaltenes.
Laboratory tests for inorganic deposits make use of 188bet asia compositional data generated in 188bet asia problem identification steps (water analysis, scaling index values, deposit XRD and XRF) to focus on selecting 188bet asia proper treating solution. Selected treating solution mixtures are run on actual field scale deposits or lab prepared analogs to determine 188bet asia effectiveness of various packages. These packages generally consist of different organic and inorganic acids, surfactants, chelators, converters and dispersants. 188bet asia preferred package is one that dissolves 188bet asia greatest amount of 188bet asia depositing compounds with 188bet asia least impact on 188bet asia production system.
3.1. Case history 1
A larger volume production well in Mexico had experienced a production decline from 13,500 barrels of oil per day to 10,500 barrels of oil per day over a six-month period. This problem was identified, through fluid analysis and laboratory instability testing, to be an asphaltene depositionproblemfor this 32APIcrudeoil. Thesinglezone limestone formation with a perforated interval of 197ft was treated with a solution of 2,300 gallons of dispersant and 25,000 gallons of solvent. This provided a radial penetration of about 7ft. 188bet asia treatment was pumped into 188bet asia well and allowed to soak for 24 hours before resuming production. 188bet asia well produced a maximum flow of 13,900 barrels of oil per day after 188bet asia treatment and 188bet asia average production rate was 13,700 barrels of oil per day for a four-month period. 188bet asia treatment effectively halted 188bet asia previous production decline rate of 600 barrels of oil per day. 188bet asia incremental barrels of oil produced over 188bet asia four- month period following 188bet asia treatment versus what could be expected from 188bet asia established decline curve was over 500,000 barrels of oil. 188bet asia cost of 188bet asia job was recovered in approximately 8 days.
3.2. Case history 2
A recently drilled horizontal sandstone formation well in California was experiencing problems. 188bet asia well was producing a high viscosity emulsion, stabilised from residuals of 188bet asia oil based drilling mud used during 188bet asia drilling operations. 188bet asia well had an initial production of only 70 barrels of oil per day and this had decreased to 50 barrels of oil per day at 188bet asia time of 188bet asia treatment. Coiled tubing was used to apply 188bet asia treatment along 188bet asia 1059-foot length of 188bet asia production zone at 188bet asia rate of 4.5 gallons per foot of perforation to achieve a 3-inch radial penetration outside 188bet asia liner. 188bet asia total job size was 4,864 gallons consisting of 2,434 gallons of crude oil and 2,434 gallons of a dispersant/solvent mixture. 188bet asia well was shut- in for 24 hours and returned to production. On day 102, 188bet asia well was producing 131 barrels of oil per day and 188bet asia well had produced 10,575 incremental barrels of oil for this period. 188bet asia increase in revenue for this well was USD 158,625 for 188bet asia 102 days.
3.3. Case history 3
A well in Southern Oklahoma was experiencing paraffin deposition in 188bet asia tubing and had to be cut on a quarterly basis. 188bet asia production had decreased from 270 barrels of oil per day to 110 barrels of oil per day over a sixteen-month period. 188bet asia well was fractured with 27,000 gallons of gelled oil containing 38,000 pounds of 20-40- mesh sand. 188bet asia production increased to 440 barrels of oil per day, but decreased rapidly to 290 barrels of oil per day over 188bet asia next seven months. Organic damage from paraffin deposition in 188bet asia formation was suspected to be 188bet asia major cause of 188bet asia production decline. This was surmised from 188bet asia positive results of 188bet asia frac job, 188bet asia rapid production decline following 188bet asia job, 188bet asia low scaling tendencies of 188bet asia water and 188bet asia history of tubular paraffin deposition. Rather than schedule another frac job, it was decided to investigate 188bet asia possibility of removing 188bet asia paraffin damage through 188bet asia use of chemical remediation. A series of six chemical jobs were conducted over 188bet asia next two years. 188bet asia organic damage was not only removed, but 188bet asia oil production was also increased to a high of 490 barrels of oil per day. This was 50 barrels of oil per day higher than that accomplished with 188bet asia frac job. 188bet asia oil production level was held above 400 barrels of oil per day for sixteen months with these treatments. Incremental oil production averaged in excess of 150 barrels of oil per day over 188bet asia post-frac value of 290 barrels of oil per day. All of 188bet asia chemical treatments were low cost with payout in less than 1 week. Additional details on this series of treatments are available in SPE 52156 [6].
3.4. Case history 4
A new in-field drilled well in California was completed with an acid job to stimulate 188bet asia well. 188bet asia well was put on a pumping unit and 188bet asia production volume was expected to be 300 barrels of oil per day based on historical off-set well initial production values. Pumping was initiated but 188bet asia well would not produce any fluids. Testing on off-set crude oil samples indicated 188bet asia oil had a strong tendency to create acid slug and rigid film emulsions when 188bet asia oil contacted 188bet asia acid without 188bet asia appropriate additives included in 188bet asia acid stimulation job. 4 drums of chemical remediation product was pumped down 188bet asia casing of 188bet asia well and allowed to soak for 12 hours overnight. 188bet asia well was put into production 188bet asia next morning and produced 350 barrels of oil per day following 188bet asia treatment.
3.5. Case history 5
Awellin Oklahomaunder CO2 floodwasexperiencing declining production and tubing deposition issues. 188bet asia crude oil was 40°API and 188bet asia well was 6,200ft deep. 188bet asia field had been under CO2 flood for 10 years. Well tests conducted once every 2 weeks for 188bet asia 6 month period prior to treatments averaged 44 barrels of oil per day, 49 barrels of water per day and 95 million Standard cubic feet per day. Fluid analysis of 188bet asia oil indicated it contained 9% paraffin with a cloud point of 110°F and a pour point of 75°F. Water analysis and scale index modelling indicated scale was not an issue. 188bet asia problem was treated as paraffin deposition in 188bet asia formation. 188bet asia well was treated with a chemical package specifically designed for paraffin remediation. Following treatment 188bet asia well was tested once every 2 weeks for 10 weeks and 188bet asia production averaged 68 barrels of oil per day, 74 barrels of water per day and 111 million standard cubic feet per day. 188bet asia cost of 188bet asia job was recovered in approximately 4 days.
3.6. Case history 6
A package of 6 wells in California was investigated for steeper declining rates than normal for 188bet asia field. Fluid testing on 188bet asia wells indicated a combination of oil wet fines and scale depositions was 188bet asia primary cause of 188bet asia production decline. 188bet asia 6 wells were treated with a combination scale dissolver and surfactant package to de-oil 188bet asia fines. 188bet asia oil production increase for 188bet asia 6 wells averaged 53.9% and 188bet asia payback on 188bet asia treatment cost was 23 days.
3.7. Case history 7
A deepwater well in 188bet asia Gulf of Mexico was experiencing rapid production decline. Fluid testing indicated 188bet asia problem was asphaltene deposition in 188bet asia formation. 188bet asia customer had a history of treating 188bet asia well with large xylene soak treatments to boost production. Historically 188bet asia well would decline to 2,400 barrels of oil per day prior to xylene treatment. Following a treatment using 400 barrels of xylene for 188bet asia 98ft of perforated interval, 188bet asia well production would increase by 1,700 barrels of oil per day to 4,100 barrels of oil per day. 188bet asia well would then start to decline again and require re-treatment on a regular basis. 188bet asia customer expectation was for an improved treatment over xylene alone that would boost production by 2,000 barrels of oil per day. A chemical solution designed specifically to remove asphaltenes from 188bet asia formation matrix was designed and 100 barrels of 188bet asia treatment was applied to 188bet asia well. 188bet asia initial production jumped 3,900 barrels of oil per day to 7,300 barrels of oil per day from 188bet asia 2,400 barrels of oil per day rate just prior to treatment. 188bet asia well averaged 6,000 barrels of oil per day for 188bet asia first 6 weeks and had decreased slowly to 4,500 barrels of oil per day after 8 months. 188bet asia incremental improvement in oil production for this 8-month period was 636,000 barrels of oil compared to 188bet asia previously used xylene treatment.
3.8. Case history 8
Well 18Dr/RP-2 of Rong oil field was experiencing paraffin deposition in 188bet asia tubing and had to be cut on a quarterly basis. 188bet asia production had decreased from 685 barrels of oil per day to 145 barrels of oil per day over an 18-month period. This problem was identified, through fluid analysis and laboratory instability testing. Fluid testing indicated 188bet asia problem was asphaltene deposition in 188bet asia formation. Organic damage from paraffin deposition in 188bet asia formation was suspected to be 188bet asia major cause of 188bet asia production decline. 188bet asia customer had a history of treating 188bet asia well with a large xylene, pour point depressant and activators treatments with parasqueeze technology to boost production. 188bet asia treatment was pumped into 188bet asia well and allowed to soak for 24 hours before resuming production. 188bet asia well produced a maximum flow of 285 barrels of oil per day after treatment compared to 145 barrels of oil per day before treatment and 188bet asia average production rate was 250 barrels of oil per day for a five month period.
3.9. Case history 9
188bet asia production of well 8011/BK17 of Bach Ho oil field had decreased from 620 barrels of oil per day to 275 barrels of oil per day over a year period. Fluid testing on 188bet asia well indicated a combination of oil wet fine and scale deposition was 188bet asia primary cause of 188bet asia production decline. 188bet asia well was treated with combination scale dissolver and surfactant package to de oil 188bet asia fine. 188bet asia oil production increased from 275 barrels of oil per day to 360 barrels of oil per day and this flow rate was maintained for 6 months.
4. Conclusion
188bet asia source and nature of organic and inorganic damage can be identified by laboratory testing and production history analysis;
Organic and inorganic damage is an ongoing process that decreases permeability and leads to subsequent oil production decline. Properly identified organic and inorganic damage can be removed from candidate wells and production restored to higher levels. Organic and inorganic damage removal by chemical treatment offers an alternative to more costly in-field drilling, fracturing and re-perforating operations;
Production gains from organic and inorganic damage remediation are transient since 188bet asia damage process is ongoing. Re-treatment at regular intervals is recommended to maximise economic return.
References
1. Michael E.Newberry. Chemical effects on crude oil pipeline pressure problems. Journal of Petroleum Technology. May 1984: p. 779 - 786.
2. Michael E.Newberry, K.M.Barker. Formation damage prevention through 188bet asia control of paraffin and asphaltene deposition. SPE 13796-MS. 188bet asia 1985 SPE Production Operations Symposium, Oklahoma City, Oklahoma. 10 - 12 March, 1985: p. 53 - 61.
3. Michael E.Newberry, K.M.Barker, K.P.Flynn. Identification and remediation of organic skin damage. 188bet asia 1999 AIChE Spring National Meeting, Houston, Texas. International Conference on Petroleum & Gas Phase Behavior and Fouling. 14 - 18 March, 1999.
4. Michael E.Newberry, K.M.Barker. Organic formation damage control and remediation. SPE 58723-MS. 188bet asia 2000 SPE International Symposium on Formation Damage, Lafayette, Louisiana. 23 - 24 February, 2000.
5. D.W.Jennings, R.Cable, Michael E.Newberry. Asphaltene stability analyses for optimizing field treatment programs. SPE170677-MS. 188bet asia 2014 SPE Annual Technology Conference and Exhibition, Amsterdam, 188bet asia Netherlands. 27 - 29 October, 2014.
6. K.M.Barker, D.B.Sharum, D.Brewer. Paraffin damage in high temperature formations, removal and inhibition. SPE 52156-MS. 188bet asia 1999 SPE Mid-Continent Operations Symposium, Oklahoma City, Oklahoma. 28 - 31 March, 1999.