Challenges in Water Treatment for the Upstream Oil and Gas Market
Unconventional resource extraction drives more demanding water and wastewater treatment issues
As global energy consumption continues its trend of rapid growth, new sources of energy must be identified and developed to meet the rising demand. In recent years, meaningful advancements in production technologies have led to significant increases in oil and gas reserves that are now recognized as recoverable.
These technologies, including the development of enhanced oil recovery strategies and novel drilling techniques, such as directional drilling, have created new possibilities in upstream oil and gas production, enabling extraction from formations that were previously too difficult or cost prohibitive to produce.
This evolution has helped drive a boom in the world’s unconventional sources, affecting the global energy markets and also leading to new and increasingly demanding water and wastewater treatment challenges.
While many treatment challenges in the upstream oil and gas market are based on rising water scarcity and tightening environmental regulations, other emerging challenges are driven by advanced recovery strategies that are now being used to produce oil and gas from unconventional sources. These enhanced oil recovery technologies – such as steam flooding, cyclic steam stimulation, and steam-assisted gravity drainage – rely on significant quantities of water and generate substantial volumes of complex brine wastewater, necessitating solutions that are both specialized and highly specific.
Source water challenges
Drought and decreasing water availability coupled with stricter water withdrawal rights for protecting freshwater resources is increasingly forcing upstream oil and gas producers to turn to alternative sources for meeting their process water needs. Indeed, in many regions where newer unconventional sources are located – including Australia, California, Western Canada and the Middle East, among others – oil and gas producers are finding very limited access to quality freshwater supplies and increasing restrictions to the use of these supplies.
These dynamics are prompting the usage of lower-quality options such as brackish water and saline water. The use of these salty water sources allows upstream production processes to operate completely independently from fresh water. The fresh water resources, including lakes, rivers and aquifers, are thereby preserved for nature and the responsible use by agricultural and municipal consumers.
Brackish water, in any case, is unsuitable for human consumption in its natural state due to the high levels of dissolved salt. However, because of these high levels of salinity, brackish water can be very problematic for employing as a feedwater in process operations, necessitating the use of advanced treatment technologies including desalination and presenting further challenges in terms of brine disposal and management.
Produced water management
One of the most challenging issues associated with the development of upstream oil and gas fields is designing a strategy for produced water management. Produced water is the water that flows from the producing reservoir to the surface, along with oil and gas, through the production well.
In some applications, such as steamtype enhanced oil recovery processes, the majority of the produced water is treated and recycled back to the process for further steam production. In other applications, such as shale play developments, the produced water is simply a byproduct and must be either recycled to another well for injection or processed for disposal. In either of these examples, there exists an excess amount of produced water that exists at the surface which needs to be disposed of. These produced water streams are usually very complex and highly saline, presenting challenges in terms of their disposal.
In some cases, where the local geology allows the development of a disposal well (defined by the EPA as Class II in the U.S.), the produced water stream can be deep well injected for disposal. If this is a possibility, it is typically the most attractive solution.
Not only does it generally represent the lowest cost solution, but it is also environmentally responsible since the contaminants present in the brine are returned deep underground where they originated and are not discharged near the surface where they would potentially contaminate fresh water resources.
In areas where deep wells are not readily accessible, trucking the produced water away often becomes the next option that is considered for disposal, but this adds liability and a tremendous cost.
For solving difficult and unique treatment challenges facing producers in upstream oil and gas recovery, treatment strategies should be adaptive and embrace a balanced, unbiased approach for utilizing the best-suited technologies based on specific conditions and circumstances.
“For solving the difficult and unique treatment challenges facing producers in upstream oil and gas recovery, treatment strategies should be adaptive and embrace a balanced, unbiased approach”
Because of the dynamics associated with unconventional sources, the most effective strategy often includes an integrated methodology – evaluating the expected performance of treatment technologies and applying combined solutions and sequences for engineering the most sustainable outcome.
In the case study below, we examine the water balance for a SAGD facility typical of those being developed in Northern Alberta for bitumen production in the oil sands.
In this case study, the SAGD facility is designed with an oil production rate of 10,000 barrels per day and has been designed to use brackish water with a TDS of 10,000ppm as make-up water to the facility. Steam is produced by a Once-Through Steam Generator (OTSG) and is injected into the reservoir at a rate of approximately 5,600 ton/day. Produced water from the reservoir has a TDS content of 4,500ppm and is de-oiled and treated to be recycled as boiler feed water (BFW).
In the base case, the OTSG Blowdown stream can be partially recycled as BFW but the ability to recycle this stream to the process is limited based on the TDS constraints inherent with the equipment design.
Overall, approximately 75 percent of the OTSG Blowdown must be sent away for disposal at a rate of 1,050 t/d. To satisfy the overall water balance, a flow rate of 1,600 t/d of brackish water must be pumped to the system to supplement the total losses from the system. The significance of these two streams cannot be overlooked at the design stage of the project, since the high make-up water