Polymer flooding in sensitive areas can require the transport of polymer fluids over long distances. Conventional wisdom limits transport distance or degradation occurs. This paper argues that critical velocity, not distance, is the controlling factor. Polymer flooding has been used to enhance the production of oil from mature fields in Oman. This article discusses the trial of several approaches to improve the treatment of water produced from these fields.
Zagitov, Robert (Cairn Oil & Gas, Vedanta Ltd) | Venkat, Panneer Selvam (Cairn Oil & Gas, Vedanta Ltd) | Kothandan, Ravindranthan (Cairn Oil & Gas, Vedanta Ltd) | Senthur, Sundar (Cairn Oil & Gas, Vedanta Ltd) | Ramanathan, Sabarinathan (Cairn Oil & Gas, Vedanta Ltd)
Enhanced Oil Recovery is important stage of life cycle of a field and often it is implemented with challenges. In the chemical EOR, challenges and surprises are expected in production chemistry and production facilities operations. Partially hydrolyzed polyacrylamide used widely for controlling mobility ratio so that Operator is able to recover maximum possible oil. With complex water chemistry and rich in positively charged divalent ions, flooded polymer having negative charge interacts with divalent ions of produced water. Back produced sheared polymer interacts with divalent ions to form semi hard to hard scales poses challenges of the reliability of production facilities.
Other important limitations to be noted in CEOR phase are using production chemicals to control scale, emulsion and microbial treatment under Hydrogen Sulphide and waxy crude environment. This paper discusses about the requirement of preparedness and how to overcome challenges of EOR operations and in handling the back produced polymer in following areas: Selection of production chemicals to be compatible to polymer so that no or minimal degradation or loss of viscosity due to polarity of chemicals Performance of production chemicals in the presence of polymer Solids loading in production system Emulsion and produced water treatment Suitability of produced water treatment facilities Revised scaling and fouling control with back produced polymer with rich divalent ions present in produced water Strategizing chemical management system to suit polymer flood and polymerized back produced water treatment regime
Selection of production chemicals to be compatible to polymer so that no or minimal degradation or loss of viscosity due to polarity of chemicals
Performance of production chemicals in the presence of polymer
Solids loading in production system Emulsion and produced water treatment
Suitability of produced water treatment facilities Revised scaling and fouling control with back produced polymer with rich divalent ions present in produced water
Strategizing chemical management system to suit polymer flood and polymerized back produced water treatment regime
Water management has always been an important part of production operation but for chemical EOR it becomes one of the critical elements as the whole water cycle needs to be analyzed and adapted to the process. In particular one key aspect that is generally neglected concerns the impact of EOR chemicals on the produced water cycle. After the chemical breakthrough, part of the EOR chemicals (polymers and/or surfactants) will be back-produced and can induce heat exchanger fouling and strongly impact oil/water separation and water treatment surface processes. All these drawbacks may lead to skewed forecasts on economic performance of EOR projects.
Some of the key challenges with produced water treatments, that facility engineers and operators will be facing when preparing a chemical EOR project, will be highlighted in this paper. A focus on some experimental results obtained within the DOLPHIN JIP – supported by 14 oil companies – will be presented. A specific laboratory methodology dedicated to the study of the impact of ASP-type chemicals on heat exchanger fouling, oil/water separation and water treatment efficiency and which mimic actual surface processes, was designed.
Results presented will illustrate the operational conditions that favor deposit on heat exchangers when polymer is back-produced. Impact of having polymers and/or surfactant within produced fluids on oil/water separation (kinetics of separation and quality of both oil and water phases) and water treatment processes efficiency (evaluated by monitoring the concentration of remaining oil in water as a function of time) will also be outlined.
This work emphasizes that water management is a major challenge for chemical EOR that needs an integrated approach and should be studied upfront. Laboratory workflows and procedures could help the de-risking of operations and try to mitigate separation issues that could advantageously be integrated into the design of chemical EOR project.
Shidi, M (Petroleum Development Oman LLC) | Mjeni, R (Petroleum Development Oman LLC) | Qayum, S (Petroleum Development Oman LLC) | Nadeem, MS (Petroleum Development Oman LLC) | Philip, G (Petroleum Development Oman LLC) | Prigent, S (BAUER Nimr LLC)
A Surface Flow Constructed Wetland System (called a Reed bed) is used as a disposal means for produced water (PW) containing hydrocarbons in a field located in the south of Oman. The Reed bed system is a farm of plants that remove oil from water, followed by evaporation ponds where the water is evaporated.
In the same field, it is planned to undergo HPAM Polymer Flood. One of the risks envisaged with this activity was the capability of the Reed bed system to handle back produced water contaminated with polymer. Therefore, a series of tests were conducted to understand the impact of polymer contaminated produced water on the Reed beds.
The experiment was carried out in two phases with a small scale experiment in batch mode followed by a long term field trial at a full scale. The first phase aimed to introduce by batches HPAM into small Intermediate Bulk Containers planted with reeds and monitored for 5 months. It was observed that HPAM resulted in an increase in the growth rate and evapotranspiration rate in some of the plants. It was clear that the HPAM did not cause any negative effects on the plants during the short-term duration of the study and the results were very encouraging.
A long term field trial was then conducted to verify the results observed from the batch experiment. To mimic the large scale Water Treatment Plant reed bed, four pilot scale (40m × 40m) surface flow wetlands were built and planted with five types of plants similar to the plants currently available, all receiving produced water with different HPAM concentrations (0, 250, 500 and 1000ppm), 0ppm serving as a control. The trial was conducted for duration of one year. The
The success criteria evaluated in this pilot were divided into two categories with critical and non-critical criterias. A critical criteria was defined as one for which a negative outcome requires significant system modifications to process produced water containing polymer. The criterias are Oil Removal, Above Ground Dry Biomass and Necrosis. The non-critical criterias such as polymer removal, plants toxic symptoms, plants health, Acrylamide accumulation and water loss imply potential minor design modifications maybe requiredto the existing Reed Bed. These criterias were developed and assessed by the company responsible for the design, operation and monitoring of the Long Term Field Trial.
The outcome was positive for all critical criteria with the exception of plant necrosis at 1000 ppm polymer. Two plants species out of five showed necrosis in the 1000ppm wetland higher than the 0ppm wetland. The Necrosis was determined to be inconclusive at 1000ppm as there were no signs of Necrosis at 500ppm and below and other factors not related to polymer are highly suspected to be responsible for this behavior. All the non-critical criteria were highly positive except for polymer removal. The wetlands did remove some of the HPAM from the produced water but not all of it. There are some uncertainties surrounding the long-term fate of the HPAM in the system for reusing the treated produced water from the wetlands. Currently, the water is evaporated after the reed beds, however the presense of polymer in it limits any further use of that water. The positive results seen during the trials have demonstrated that there is no risk on reed beds when processing up to 500ppm HPAM.
Leitenmueller, Verena (Mining University Leoben) | Wenzina, Johannes (Technical University Vienna) | Kadnar, Rainer (OMV Exploration & Production GmbH) | Jamek, Karl (OMV Exploration & Production GmbH) | Hofstaetter, Herbert (Mining University Leoben)
Nowadays, the injection of dilute hydrolyzed polyacrylamide (HPAM) solutions after water flooding operations is a promising tertiary recovery method. However, the treatment of produced water containing breakthrough polymer plays a challenging aspect in the oil and gas industry. Ensuring good filterability of the produced water for further usage, either pressure maintenance or EOR application, is still a critical issue. Polymer loads in the produced water need to be expected, which can massively influence the separation efficiency of the water treatment system. Especially, the handling of polymer-containing water streams and finding the appropriate technology for the treatment, chemically or mechanically, has a decisive influence on performing a full-field roll out of polymer flooding activities.
Aim of this work was to study the impact of back-produced polymer on the water treatment process and to reach the desired injection water quality. Therefore a water treatment plant in pilot scale was used. The unit simulates the main process steps of the water treatment plant Schönkirchen in the Vienna Basin (corrugated plate interceptor, dissolved gas flotation unit, and nutshell filter). The maximum back-produced polymer concentration, which can be handled within the system, was determined. Two different chemical sets (coagulant and flocculant) were tested, regarding their oil and solids removal ability, in presence of different polymer concentrations.
At the end of the field study, one of these chemical sets was found, having a hydrocarbon removal efficiency of around 99% in presence of 30 ppm HPAM inlet concentration. Using this set, good removal efficiency and no plugging of the nutshell filter was observed even at high polymer concentrations. The other set led to plugging of the filtration system at relative low polymer concentrations of 8 ppm HPAM and the removal efficiency of hydrocarbons as well as polymer was poor. Based on these results, it can be assumed that the processes of the water treatment plant Schönkirchen are not negatively affected in the presence of up to 30 ppm polymer load in the inlet water stream.
Ma, He (King Fahd University of Petroleum & Minerals) | Abdullah, S. Sultan (King Fahd University of Petroleum & Minerals) | Shawabkeh, Reyad (King Fahd University of Petroleum & Minerals) | Mustafa, S. Nasser (Qatar University)
Surfactant and polymer flooding technology can greatly enhance the oil recovery through the expansion of sweeping and displacing efficiency. The recovered oil from surfactant and polymer flooding emulsifies the residual chemical, which makes the separation of water from oil quite difficult, yet the impact of the enhanced oil recovery (EOR) chemicals on the produced water cycle is generally neglected in chemically-based EOR studies. This includes compatibility of EOR chemicals with the additives used to pre-treat the injected water or change reservoir wettability and result in producing oil/water emulsion after EOR breakthrough.
The largest waste produced in oil and gas industries is believed to be the produced water, as it contains different sort of organic and inorganic admixture. There are a number of treatment methods available for produced water. To separate water from oil in a much efficient manner and to reach the emission standard, a new class of water soluble polymer of polyacrylamides (PAMs) was used as destabilizing agents for water-oil emulsions, which have been stabilized by surfactant (Tallowamine Acetate).
The impact of the surface charge form, the density of polyacrylamides in turbidity -reduction, zeta potential, COD, FTIR, viscosity and volume of separated water were explored in this study. Different anionic polyacrylamide of different surface charge density were evaluated. Different anionic polyacrylamides were utilized, and at optimum dosage, anionic AN 934 PAM at its optimum concentration was proved as the best way to reduce the residual turbidity compared with other PAMs mentioned in this research. The effect of the different salinity (salt content: 200,000 ppm brine and 57,000 gulf seawater) of produced water will be evaluated using different PAM with different charge density as optimization. The results showed that the W/O emulsion stability related with its salinity, while the optimum concentration of demulsifier are same at both high and low salinity.
Research has discovered systems that can selectively flocculate mineral solids from a high molecular weight polymer flood matrix while leaving the polymer intact or alternatively achieving a viable total flocculation of the polymer in the produced fluids. Modified alkaline surfactant polymer (ASP) and standard polymer (P) flood systems were studied with findings obtained by controlled variations of both well-proven and non-prevalent chemical approaches. Results concluded that selectively removing the mineral solids from polymer-laden water produces reusable enhanced oil recovery (EOR) fluid.
EOR is a proven method to increase hydrocarbon yield from post-natural, stimulated, or standard flood driven reservoirs. Fluid produced from the reservoir contains the desired hydrocarbon and an aqueous phase. Previously considered a liability, properly treated, the aqueous phase can become an asset. Polymer floods have a proven history in EOR and, though complex in application, ASP also demonstrated EOR effectiveness in the laboratory. Most ASP approaches are currently in field trial stages. The produced fluid is subjected to hydrocarbon separation with the resulting aqueous system either treated for disposal or recycled into the system. The aqueous phase matrix is mainly composed of high molecular weight polymer, mineral solids, residual base, residual oil, and possibly surfactant. If the producer chooses disposal, the solids must be flocculated by a method balancing density, dewaterability, processability, process variability, and cost. However, if the producer opts to recycle the fluid for reinjection, steps must be taken to minimize polymer deviations requiring selective flocculation of all components with exception of the polymer. This undertaking is challenging as EOR polymers are also effective flocculants, therefore sensitive to standard coagulant and flocculant approaches. Utilizing controlled, standard methods and multivariable design of experiments, results were obtained for both total and selective flocculation.
Total flocculation systematically studies the influence of pH, inorganic, and organic coagulants in maximizing the treatment effectiveness. The same approach was successful for selective flocculation, however unique coagulants were applied. The selective flocculation process coagulated and separated the mineral solids, and left the high molecular weight polymer intact and the fluid matrix as viscous as prior to treatment. Effectiveness of treatments were determined using standard gravimetric and viscometric methods.
These discoveries will assist decision makers in determining whether total or selective flocculation is the most viable treatment for polymer based EOR, balancing environmental and economic aspects to pursue a desired treatment route. These methods, though targeting EOR, have practical applications for treatment of flowback and water produced from stimulation and potentially drilling operations as well.
A side effect of EOR polymer flooding on topsides process chain is the generation of stable thin emulsion in viscous water phase. Both viscosity and severe emulsion impede the efficiency of water treatment technologies. The viscosity of the back produced polymer increases the time of clarification of oily water phase. The target of the water treatment specialist would be to collapse the viscosity of the produced water.
The main concern is to decrease the viscosity of the produced water containing polymer back produced, acting on the degradation of the polymer without generating more severe oily emulsion. Shearing, a well known mode of degradation has been compared to other techniques such as chemical oxidation (bleach) and sonication. All the tests were performed with a high molecular weight polyacrylamide commonly used in EOR; at bench lab scale on synthetic viscosified produced water and on back produced water from field with cEOR flooding. Degradation efficiency was evaluated through viscosity measurements and polymer molecular weight analyses.
This paper presents the results of the different investigations carried out to drop the viscosity of the produced water to an acceptable value for water treatment. Chemical oxidation using bleach has proved its efficiency on synthetic produced water. Different shearing conditions and different powers of sonication have also highlighted actions on the polymer and on the viscosity of the water phase.
Even if all the tested degradations lead to a significant viscosity drop of the synthetic viscosified water, the improvements on water treatment were not equivalent. Analytical measurements of the molecular weight of the degraded polymer allowed initiating a scale of degradation efficiency.
The efficiency, feasibility, difficulty, beneficial impact on water treatment and level of readiness of the technology have been estimated. An assessment of the different techniques for the polymer degradation in water treatment is presented at the end of this paper.
The feasibility to decrease the viscosity of the back produced water would allow to simplify the water treatment process chain dedicated to polymer flooding case. Works continues on integrated water treatment process, including pre-degradation of the polymer back produced.
Polymer flooding is used as a secondary or tertiary recovery mechanism to enhance oil production and increase oil reserves. In such situations, part of the injected polymer will be back produced at the topsides at different ratios depending on the injection mode and along field life. The side effects of polymer flooding on the topsides process chain are identified as manageable trouble regarding oil/water separation, and major issues at the water treatment stage.
The presence of polymer in the produced water increases the viscosity and the severity of the emulsion. Literature dealing with viscosified water has already highlighted decreases of efficiency of water treatment technologies such as hydrocyclones, flotation, generating inadequate water quality for produced water reinjection (PWRI). A common way to optimize flotation on field is to inject additives. But the polymer impedes the action of conventional chemicals used in O&G Production.
Chemicals usually help to improve the water quality, regarding constraints of PWRI. This paper focuses on chemical approach along the separation and water treatment chain in case of back produced polymer.
For this study, we used HPAM, a high molecular weight polyacrylamide commonly used in EOR. Previous works on conventional water treatment additives have shown a high consumption of chemical to clarify viscosified water, which is not economically practicable.
Therefore, we proposed to explore another approach, first taking care of water quality upstream at the separation stage, then pursuing on chemical optimization at the water treatment stage.
At first, a lab methodology for separation studies was developed to generate a thin emulsion with controlled degradation of the polymer, simulating the characteristics of the back produced viscosified water on field. A screening of demulsifiers was carried out on emulsion containing 10% oil and synthetic polymer back produced water (up to 500 ppm HPAM). These tests have shown that water quality can be improved at the separation stage, at conventional dosage at lab scale. The remaining oil in water for 10% initial oil, depending on the residence time, is maintained in the range of few tens to few hundreds ppm. Water treatment optimization reference case was then based on few hundreds ppm of remaining oil.
For water treatment studies, oil in water emulsions were prepared by mixing oil with synthetic or real viscosified water (up to 500 ppm HPAM) with an ultra-turrax homogenizer. Different types of clarifiers ranging from 50 to 100 ppm were evaluated. These tests have shown that water quality can be improved using a combination of adequate additives. These bench lab results were confirmed on a lab conventional technology, and could be further evaluated in field trials for an integrated solution.
Management of produced water containing back produced polymer (HPAM) is a real challenge since its limited biodegradability and its relatively high concentration in produced water (up to few hundreds of mg/L) make it difficult to discharge into surface water. The preferred option is to conduct Produced Water Re-Injection (PWRI). When PWRI requires stringent water specifications as low as 10 mg/L of dispersed hydrocarbon (HC), 2 mg/L of total suspended solids (TSS) and 5 µm particle cut size (d100), tertiary treatments become mandatory. It is, for example, the case for PWRI in matrix mode for unconsolidated and shallow sand reservoirs. The objective of this study was to better understand the impact of HPAM polymer on tertiary treatment with a focus on ceramic membrane performances in order to optimize the design of produced water treatment facilities.
Maturity assessment of these water treatment technologies highlighted numerous major risks in presence of polymer. A R&D plan was then conducted on labscale prototypes using synthetic Produced Water (PW) containing polymer.
The tests performed with low pore size membrane (< 1 µm) met the specifications but the polymer was retained by the membrane which caused severe fouling and thus low productivity. Inversely, with pore size larger than 1µm, the polymer went through the membrane which strongly enhanced the productivity. However, with such large pores, the specifications are not anymore guaranteed. Two strategies were then identified and tested: (i) combine coagulation and membrane filtration or (ii) combine oxidation and membrane filtration using low pore size membranes. The use of coagulant (FeCl3) was very effective to precipitate the polymer and improve filtration performances but the management of the waste stream containing tons of precipitated polymer turned into a major showstopper. Inversely, the use of oxidation as a pre-treatment breaks polymer chains that become small enough to go through the membranes which (i) strongly improves membrane performances and (ii) enables the polymer re-injection.
This combination was successfully tested in batch but also in continuous mode using commercial membranes. The performances were then compared with other type of tertiary treatment technologies such as media filter (sand and walnut). In the context of PWRI in matrix mode for unconsolidated sand reservoirs (or any case that would require such stringent water specifications), membrane technology combined with oxidation is today a promising option deserving qualification tests at a larger scale.