Study On Spectral Properties Of Oilfield Wastewater And Its Oil Content Measurement

Most land oilfields in our country have entered high water cut stage,of which the water content of Daqing Oilfield is as high as 90%.While enhancing oil recovery,a large amount of oilfield wastewater is also produced.In the method of oil content measurement,optical measurement has the characteristics of fast non-contact and it has a wide application prospect.However,the complex components of the oilfield wastewater have brought some difficulty to the measurement of oil content.At present,there is relatively little research on on-line measurement of oil content based on the optical properties of oilfield wastewater,and the main problem is the lack of effective optical properties of oilfield wastewater and the logical relationship between it and oil content.The oilfield wastewater of a joint station in Daqing Xingbei Oilfield was selected as the research object.The optical properties,including the spectral properties and optical physical parameters,were studied by measuring the transmittance spectral of oilfield wastewater.A double thickness inversion model was constructed to calculate the optical physical parameters.The effects of different factors on transmittance spectral and optical physical parameters were analyzed.Finally,the relationship between optical properties and oil content of oilfield wastewater was obtained.The main contents of this paper are as follows:(1)By introducing the concept of equivalent transmittance,a double thickness inversion model for retrieving the optical physical parameters of oilfield wastewater was established.And the optical physical parameters of distilled water were measurement for verifying the inversion model.The experimental results show that the model can be used to solve the optical physical parameters of oilfield wastewater.(2)The transmittance spectral of oilfield wastewater was measured,and the influence of temperature,p H value and content of polymer on the transmittance spectral of oilfield wastewater was analyzed.The experimental results show that the transmittance of oilfield wastewater decreases with the increase of oil content.In the range of 10-70℃,the transmittance of oilfield wastewater increases with the increase of temperature.When the p H value is in the range of 5.3-11.9,the transmittance of oilfield wastewater varies irregularly with the p H value.The transmittance of oilfield wastewater decreases with the increase of the content of polymer in the range of 0-400mg/L.(3)Based on the transmittance spectral of oilfield wastewater,the optical physical parameters of oilfield wastewater,including absorption index k,refractive indexn and absorption coefficient α,were obtained by combining the double thickness inversion model.The experimental results show that k and α increase with the increase of oil content,but while the n is irregular.The k and α decrease with the increase of temperature in the temperature range of 10-70℃,but while the n is irregular.When the p H value is in the range of 5.3-11.9,the optical physical parameters of oilfield wastewater have no regular with the p H valuechange.When the content of polymer is in the range of 0-400mg/L,k and α increase with the increase of the content of polymer,but while n is irregular.(4)The measuring device of the transmittance spectral of liquid in the flow state was built.The transmittance spectral of oilfield wastewater in flowing state was measured,and the influence of flow state on transmittance spectral of oilfield wastewater was analyzed.The experimental results show that the relative error caused by the change of flow state is smaller and the maximum error is not more than 2.5%.It shows that when the error is in the allowable range,the transmittance of oilfield wastewater in static state can be used to characterize the transmittance in flow state.(5)Based on the optical properties of oilfield wastewater,254 nm and 400 nm dual-band were selected,and the optical properties and oil content of oilfield wastewater were fitted by least square method,including the transmittance of optical cell filled with oilfield wastewater,the transmittance of oilfield wastewater and the absorption coefficient of oilfield wastewater.The research results in this paper can provide theoretical support and data reference for the future research of transmittance spectral of oilfield wastewater and the online measurement of oil content of oilfield wastewater.