Hydraulic fracturing using conventional slick water or gelled water jobs requires large volumes of water. Historically it has required relatively fresh water. In modern horizontal wells with scores of individual stages it may not be economically attractive to use portable frac tanks. Operators may dig frac pits that may or may not be lined and may be exposed to the atmosphere for a considerable period of time prior to the fracture treatment. Frac water sources include fresh water supply wells, chlorinated city water, rain water, ponds, rivers, streams, lake water, and frac flow back water from other wells. Often several different water sources are mixed, leading to the potential for significant scale formation and enhanced bacterial and algal activity.
The need for fresh water for a large development campaign may be so great that it is material compared to the local needs for fresh water, particularly in very dry areas or those under drought or water shortage conditions. Even in areas with very substantial groundwater resources, the prospective need for water in hydraulic fracturing may cause governmental regulators to limit conventional approaches for water necessitating improved disposal and re-use. This may require high costs for trucking of fresh water and lead to costly water disposal costs. The fracturing process can enable downhole growth of bacteria (cooling the near wellbore region and introduction of new bacteria). Microbial induced corrosion from sulfate-reducing bacteria (SRBs) and other bacteria can increase corrosion, decrease the natural gas and/or condensate product value, increase cleanup costs dues to the production of iron sulfide in the water, generate require costly treatments and pose safety hazards.
Scale deposits can occur when mixing fluids from different sources or the interaction of the formation minerals including barium, strontium, calcium and bicarbonate with high sulfate frac water. Many resulting scales such as barium sulfate or strontium sulfate are quite difficult to treat. In many cases the barium and strontium ions have radium ions associated with them which will result in the formation of radioactive scale deposition as Naturally Occurring Radioactive Materials or NORMS. While there are many sources of NORMS, their treatment and safe disposal is costly. The following figure illustrates the level of barium sulfate scaling observed in a flowline from a single Haynesville shale gas producer in one month.
BaSO4 Scale in Haynesville Shale flowline after one month
While reservoir engineers may not be intimately familiar with corrosion and scaling issues, they must be more familiar with these issues in the case of shale reservoirs. The level of water production and realistic limitations on well performance means that the job of the reservoir and production and completions engineers remain closely intertwined. It is critical to plan early and conduct a detailed survey of the total fluid system from hydraulic fracturing through production. When this is completed, production chemistry and completion experts can design appropriate programs including necessary:
– Scale Inhibitors
– Corrosion Inhibitors
– Oxygen Scavengers
– Flow Stimulators
– Friction Reducers
– Clay Stabilizers
Diligent monitoring, testing and reporting can then lead to optimization of costs, production rates and ultimate recovery.
Disposal of produced water, particularly flow back water from hydraulic fracturing operations is done many different ways depending on local capabilities and regulations. Operators will want to reuse produced water if possible. In the early stages of flow back following a hydraulic fracturing treatment, produced waters often have relatively low Total Dissolved Solids (TDS); this water can be used relatively easily in subsequent hydraulic fracturing jobs. Higher TDS waters are often trucked or pipelined to central facilities for disposal via a deep (well below fresh waters) disposal well or occasionally through permitted discharges or cleanup treatments in central facilities. Some of the higher TDS water could instead be processed (demineralized) with the fresher part of the water being reused and the higher TDS fraction of the water being handled through central facilities or deep well injection.
Produced water cleanup could include demineralization to lower TDS and suspended solids, removal of hydrocarbons such as oil, grease, benzene, etc. mechanical demineralization approaches include thermal evaporation/condensation approaches and reverse osmosis. Some areas with plentiful surface acreage can use natural evaporation. Other mechanical approaches with less frequent usage to date include crystallization, filtration and freeze-thaw evaporation.
Baker Petrolite offers the AddFrac™ measurement and control services as a single-source, complete frac additive programs that ensures trouble-free, low-risk frac operations. These chemical services reduce frac job costs, boost production, and reduce costs during the field life cycle.
Baker Hughes products and services include:
Other Baker Hughes services including corrosion control, EOR services and bacteria management services are addressed on Baker Hughes’ website. Baker Hughes’ Reservoir Development Services offers consulting services in production chemistry that can be integrated with hydraulic fracturing or water injection or disposal operations.