Well, water life cycles must be integrated to design water system achieving both environmental, cost benefits
By Sahar Mouallem, Baker Hughes
Water is essential to oilfield operations. However, already limited water resources are increasingly in demand. Growing populations, climate change, water limitations and increasing water demand are resulting in unmet needs and changing expectations – all of which lead to greater public scrutiny and regulatory oversight of water resources.
The majority of shale resources worldwide are sitting in areas of high water stress or arid conditions. With 386 million people living on the land above these resources, the importance of water in energy production is becoming evident across the globe as the search for solutions increases.
Extraction of shale gas through hydraulic fracturing requires large quantities of water to fracture the gas-bearing shales and unleash their potential for production. Currently, water use for fracturing accounts for only 1-2% of total water consumption in the United States. A typical hydraulic fracturing operation requires 2.5 million to 4 million gallons of water. In 2014, the estimated water consumption for hydraulic fracturing is over 2.2 billion bbl. This is forecast to grow to more than 3 billion bbl by 2016.
More than 24 billion bbl of produced water are estimated to result from hydraulic fracturing in the United States in 2014. The largest portion of that will come from mature conventional oil and gas wells. Standard practice has been to dispose of it via reinjection, but the logistics of moving water has economic and potential environmental impacts, such as issues associated with trucking.
Water takes center stage in the production of unconventional resources. The growth of unconventional resource development, along with water limitations throughout North America, calls for a smart water management plan. This plan includes water sourcing and recycling solutions for flowback and produced water. Sourcing, storage, logistics, production and disposal of water represent significant costs to the oil and gas industry, but new methods are evolving that reduce cost, as well as potential environmental impacts.
Smart water management integrates the well and water life cycles to holistically design a system that reduces, controls and reuses water. This approach reduces unproductive water in the formation, proactively controls water-induced issues (such as scaling and bacteria), and maximizes reuse of produced water. The results are better productivity, less freshwater usage, better logistics (reducing heavy truck traffic) and improvements to the environmental footprint.
Produced water is an inevitable byproduct of the hydrocarbon production process. More than 90% of it is associated with conventional wells. In these wells, water volumes increase over time due to the nature of the process.
Water inflow into the well can be caused by recompletion problems or problems beyond the wellbore. Near-wellbore problems – such as casing leaks, flow behind pipe and unfractured wells with effective barriers to crossflow – can be addressed with mechanical tools. However, for problems deep in the reservoir, like a natural fracture system leading to an aquifer or a fracture connecting a pair of wells, repair beyond the wellbore is required.
Chemical reservoir solutions are best suited to address these more difficult reservoir problems. Subsurface water shutoff and conformance treatments effectively decrease unproductive water in producing wells. Minimizing water production at the source reduces the energy required for lifting and trucking, which translates into less associated emissions and road damage. Success of these applications is highly dependent on the correct problem diagnosis, followed by the right job design and application of correct conformance chemicals.
An operator in West Texas had 56 wells that were at the end of their economic life in the Spraberry Trend, which is composed of naturally fractured sandstone that sits on an aquifer. The wells’ production had dropped to 100 bbl/day, with more than 6,000 bbl of water per day (BWPD). After treating all the wells with chemical conformance solutions, production increased by more than 200% to 325 bbl/day, while water decreased to less than 4,000 BWPD. Three years later, 34 of the wells maintained those production rates. This means that more than 2 million bbl of water were not produced, removing the demand for more than 21,000 truck trips for disposal.
In another example, chemical water conformance treatments revived a nonproductive well in the Permian Basin. Water inflow from the formation was flooding out oil production. Although the well was not producing any oil, 400 BWPD were being produced. After treatment, oil production increased to 30 bbl/day, and water decreased to 100 BWPD. The operator saw immediate savings in operating costs associated with the produced water. Production volumes remained constant a year after treatment.
The makeup of the water is impacted by the reservoir rock characteristics, the wellbore and surface handling techniques. Reservoir temperature and pressure, as well as naturally occurring elements in the reservoir, can also impact the water chemistry. Inevitably, produced water causes issues like scale, corrosion and bacteria, which reduce productivity and add to operating costs. Mitigating these issues is crucial to maintaining hydrocarbon flow, well integrity and reducing HSE risks.
An operator in the Haynesville was hydraulically fracturing its wells with water from a paper mill containing elements associated with scaling tendencies. Liquid treatments, in this case, provided short-term inhibition, and the wells needed bi-weekly interventions. By applying a proprietary solid scale inhibitor on seven of the wells, the need for costly intervention was eliminated. The operator saved in excess of $2 million over a one-year period.
To use less freshwater for fracturing, new solutions are being employed. Operators are exploring sourcing from brackish aquifers, wastewater effluent from municipalities, and recycling and reusing flowback and produced water. Another option is blending freshwater with oilfield waste water because many fracture chemistries can support fracture fluids with high total suspended solids and total dissolved solids levels.
Virtually any oilfield water can be treated; it is all a matter of economics. The technology exists today to convert unwanted water into a reusable resource onsite, further reducing disposal, trucking and carbon emissions. Surface water treatment solutions using environmentally preferred biocides, electromechanical processes, separation and filtration enable operators to reuse produced and flowback water in hydraulic fracturing fluids. Finding effective ways to convert produced water into a valuable asset could mitigate any potential environmental and safety issues associated with current disposal practices.
Working in the Caddo limestone formation in Baylor County, Texas, an operator faced water availability and cost challenges that required the trucking of freshwater for completions from three adjacent counties. Analysis and testing determined the in-field produced water could be effectively treated for reuse, reducing water-handling costs, trucking and related emissions. A total of 27,547 bbl of produced water were treated onsite and reused in a 17-stage crosslinked hydraulic fracturing system. This reuse program directly reduced the amount of freshwater by the same amount, reducing injection disposal volumes by 98%.
In the Marcellus, an operator needed a solution for treating water retained in multiple earthen impoundments. The water in these impoundments contained significant bacteria, dissolved iron, hydrogen sulfide (H2S) and iron sulfide (FeS), resulting in poor water quality and unpleasant odors that limited the water’s hydraulic fracturing reuse. The contaminants not only posed a potential safety risk during fluid handling and fracturing operations but also could negatively impact the fracturing fluid.
Approximately 300,000 bbl of water were treated with chlorine dioxide (ClO2) prior to it being blended with freshwater for fracturing operations. The treatment resulted in an eight bottle log reduction in bacteria and complete oxidization of FeS and H2S. The odor was eliminated, and water clarity improved significantly. Ultimately, the operator saved more than $640,000.
The technology and expertise exists today to convert the industry’s largest waste product into a reusable resource, such as hydraulic fracturing fluid, enabling water recycling and reuse to become a standard practice in the oilfield.
The oilfield water problem is complex. Smart water management, however, means looking beyond symptoms and applying incremental improvements to solve it one step at a time. By applying the principles of smart water management strategically (reduce, control and recycle), the benefits go well beyond operating expense economics. These savings are reflected in substantial environmental benefits, such as a drastic reduction in freshwater demand (conservation), minimizing heavy truck traffic (safety), lowering diesel emissions (carbon footprint) and turning waste into a usable product (recycling).