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Abstract Demand for water used in hydraulic fracturing is increasing continuously due to the implementation of oilfield technologies such as horizontal wells and multistage hydraulic fracturing. The rising cost of fresh water has motivated services and production companies to try to prepare fracturing fluids with less ideal water sources such as produced water and seawater.
Technically it is not too difficult to make fracturing fluids for medium-to-low temperature applications using salt water like produced water or seawater. However at high temperatures of, for example, 300°F or more, it is much more challenging to formulate stable fluids directly with untreated salt water due to the damages related to the high levels of salinity and hardness in the water. With innovative approaches and careful selections of fluid additives in our tests, potential fluid issues caused by low water quality and harsh downhole temperatures were resolved or mitigated.
A novel high-temperature fracturing fluid system was invented recently that could be prepared with untreated seawater having a TDS of, for example, about 57,000 mg/L. The fluids comprised of metal-crosslinked polysaccharide polymers, and remained stable at high temperatures of 300°F or more. In a typical test, the fluid viscosity stayed above 500cP (at 40/s shear rate) for at least 60 minutes at 300°F. The fluid stability could be further enhanced with the addition of a number of selected nanomaterials. For instance, when one of the nanomaterials was added to the above fluids at a dose of 0.02% by weight or less, the lifetime of the fluid viscosity above 500cP was extended by at least 30%. Tests also showed that, with the addition of the nanomaterials, the viscosity lifetime could remain the same even when the polymer loading was reduced. The fracturing fluids also consistently showed over 90% regained permeability in both coreflow and proppant pack conductivity tests. Overall, the novel seawater-based fluid system shows excellent high-temperature stability, minimum formation and proppant pack damage, and intrinsically low scaling tendency.
The synergetic behaviors among the fluid additives and the nanomaterials in the high-temperature fracturing fluids prepared with the untreated seawater will be discussed, and the field-related laboratory test results will be presented in detail.
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