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.

This study is about scale squeeze application for ASP pilot that was carried at Marmul field. This is first kind of scale squeeze treatment for ASP application. High pH associated with the ASP slug injection and production (pH>10.5) provides a rich environment for scale precipitation of metal ions when mixed with injection water. (1) Multiple activities associated with the scale squeeze treatment (evaluation, screening, modeling and application) were carried out from 2008 – 2016 in-house as well as with different vendors. It was quite challenging to find suitable scale inhibitor which is capable for scale inhibition at elevated pH and has longer squeeze life time. The squeeze application was designed to start with a pre-flush stage to displace tubing fluids, acts as a spacer, condition the formation near the well bore and prevent water blocks/emulsions, followed by a main flush stage that has the highest concentration of SI in the mixed brine. Later on, a post flush stage was injected to displace the main flush further into the reservoir and increase adsorption. Finally, tubing displacement is injected which was about 5 m3 for each well. The scale squeeze treatment for the four MM ASP production wells was completed prior to the ASP slug injection. A shut-in period for each well was applied to ensure adsorption of the chemical to the reservoir rock. Monitoring of the scale inhibitor return profile after the squeeze treatment for each well was carried out to determine the flow back characteristics and to evaluate the efficiency of the treatment. The monitoring evaluation has indicated that the scale squeeze treatment was successful in inhibiting the formation of scale in all of the four production wells and the concentration of the scale inhibitor was above MIC of 10 ppm. The scale inhibitor return profile concentration was also found to be in a very good alignment with the theoretical model and the treatment efficiency is passing the six months treatment life time period. This was successful implementation and proved the concept of appropriate propagation of SI from the formation to production system.

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 Figure 1 shows the long term field trial. 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.

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.

Chemical EOR is starting to pick-up in the industry in the last 10 years due to the high oil cost and lower chemical costs. Preparing the solution for injection is the well established part of the process. However, treatment of the fluids coming from chemical flooded projects is one of the main risks associated with Chemical EOR processes. There are a number of processing difficulties which is caused by the back produced chemicals. Including tighter emulsions, heater fouling and other water treatment challenges. The back produced polymer is recognized as a risk that need to be addressed and mitigated as early as possible for any polymer project. In a field in the Sultanate of Oman, a polymer flood project was initiated early 2010. As part of the project, induced gas flotation and filtration units were installed in order to treat the produced water to the required specification for polymer solution preparation and injection. The required specification is 5 ppm (w) OIW and 2 ppm (w) TSS at the outlet of the filtration stage. This specification is required for polymer preparation and water injection. The molecular weight of the polymer coming back from the reservoir was measured to be in the range of 7 to 10 million Dalton molecular weight. Induced gas flotation technologies are accelerated gravity separation process. If the viscosity of the continuous phase increases, the raising velocity of the oil droplets reduces. It is then very essential for the viscosity of the continuous phase (water) to be maintained. It was found that the performance of the flotation cell decreases dramatically if the viscosity of the water increases more than 1.5-2 cP (at 7.0 s -1 shear rate) by using bench-top IGF trials. Mechanical and chemical means of breaking the HPAM polymer is investigated in this paper to decrease the viscosity of the produced water to a level that will enable the flotation technology to maintain performance to allow a method to be used in the field where these conventional technologies has been already installed. A success criteria was set which is the ability of the method to reduce the viscosity to the range of 1.5 – 2 cP. In terms of mechanical means to break the polymer, it was found that shearing through valves by differential pressure of 40 bars decreases the viscosity to about 2 cP using both higher molecular weight polymer or lower molecular weight polymer and it was more effective than 3-stages centrifugal pump. The main disadvantage of the mechanical shearing is the formation of smaller oil droplet through the shearing and smaller oil droplet which means slower raising velocity in the flotation cells. An attempt was carried out to quantify the effect of the pressure drop on the droplet size distribution. However, the starting droplet size was already in the range of 10 micron. It was observed that there is a small reduction in the droplet size from 10 micron to around 7 microns when the pressure drop is about 40 bars. In terms of chemical means to break the polymer, Sodium hypochlorite was the most effective chemical to break the HPAM polymer. The required dosage rate is in the range of 50 −100 ppm to achieve 1.5-2 cP (at 7.0 s -1 shear rate). In the presence of H 2 S in the water, it was observed that the dosage rate increases to about 500-1,000 ppm which makes it uneconomical to be implanted in the field. The oxidizer preferentially reacts with H 2 S to form a colloidal suspension.