Treating and reinjecting produced water containing polymers is one of the major challenges to overcome in the field of chemical enhanced oil recovery (EOR). The TRESEOR pilot project and reinjection field tests carried out by Total in 2016 represent a new step forward in gaining the experience and expertise essential to the cost-effective roll-out of this line of technology.
TRESEOR, leading expertise in water treatment
For Total's assets portfolio, major stakes are in play with this improved technique for recovering hydrocarbons through the injection of chemicals (polymers and surfactants). As such, the technology is a priority for R&D. The subject is a strategic one in terms of maximizing the Group's oil production, and we have undertaken many projects in relation to it. The objective is decisive: reducing costs, which is key for this line of technology to become operational.
To take up the challenge, we need to optimize the entire chemical EOR chain, from the reservoir to the surface. Already, the advanced expertise in physical chemistry at our PERL design and research unit in Lacq, combined with feedback from various chemical EOR industrial pilot projects, have put us at the forefront of this technology.
We were the first to meet the challenge of offshore polymer injection, which we tested from 2008 to 2012 in a pilot project at the offshore Angola Dalia oilfield. In 2013, we marked another first by running a pilot test of polymer transport at the surface level at Wyoming's Rocky Mountain Oilfield Testing Center in the United States. The aim of that test was to characterize and model the rheology of polymer-viscosified water during transport. The following year, we undertook a chemical EOR pilot demonstration at the ABK oilfield in Abu Dhabi. That confirmed the effectiveness of surfactants formulated in our laboratories to extend the field of action of chemical EOR to the challenging context of a hot and highly saline reservoir in the Middle East.
In 2016, the TRESEOR (TREatment Suitable for chemical EOR) pilot project advanced our understanding of and control over another link in the chemical EOR chain: the treatment of produced water containing polymers.
Combined control over environmental impacts and water treatment costs
One of the key factors in the environmentally responsible and economically viable development of chemical EOR will be developing a treatment method suitable for produced water made viscous by the presence of polymers. The objective is to have technologies that will:
- effectively filter out solids and separate the hydrocarbons to produce water clean enough to be reinjected, so we can recycle that water and avoid disposing of it in the environment;
- let the polymers pass through the filtration process and limit their degradation, in order to re-use them and thereby limit the addition of “fresh” polymers (and the ensuing cost) to make the treated water reach the level of viscosity required for injection water.
The solution developed and validated in our laboratories combines an oxidation process with an ultra-fine filtration method using a ceramic membrane (CCFU: Ceramic Cross Flow Filtration). The validation of this process on an industrial scale was the main objective of the TRESEOR pilot test, which we carried out in collaboration with OMV at the Matzen oilfield in Austria between October 2015 and July 2016.
The test unit had a treatment capacity of 40 cubic meters of water per day (approximately 6.4 BWPD), and was installed upstream of a well that delivered produced water containing 150 ppm of polymers. This allowed us to test the effectiveness of the filtration membranes at a range of pore thresholds, with and without pretreatment by oxidation, and at different polymer concentrations. The performance results were also compared to those obtained using traditional media filters (sand and walnut shells).
With those results, we were able to define the functioning parameters of the CCFU (flow rate, quantity of oxidant, frequency of cleaning the membranes, etc.) and identify avenues of improvement. Those will be evaluated during a second TRESEOR test phase, which will also test the alternative treatment technology of centrifugation.
From water treatment to injection
To further advance our investigations, we added a permeability reduction test (PRT) upstream of TRESEOR, by injecting produced water into the reservoir rock. This is the only type of test that delivers the information needed to predict the long-term capacity for injecting produced water.
In this way, we were able to compare injectivity losses, which were measured using unconsolidated sand and sandstone cores, for water treated by TRESEOR with various configurations and for produced water that was untreated and directly sampled from the separator outlet. Those measurements show a much slower loss of injectivity for water filtered using the CCFU process compared to traditional media filters.
For the first time, we were also able to test the degradation of cores by water containing higher levels of polymers, across a range of 500 to 800 ppm. The challenge was to get close to the operational conditions of a chemical EOR project, to advance our understanding of the long-term impacts of the solution's viscosity on injectivity.
The permeability reduction tests are to be completed during the second phase of the TRESEOR project, when we will test the injectivity of produced water containing polymers treated by centrifugation.
Research & Development
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