Study On The Temperature Limit Of Unheated Gathering Of Waxy Crude Oils With High Water Cut In Jilin Oilfield

As Jilin oilfields gradually enter the end of development period,the water cut of produced liquid has been bocoming larger,which significantly increases the energy consumption of gathering systems.At the same time,the flow ability of oil-water mixtures have been improved,which enables the no-heating gathering for oilfields.Once the gathering temperature of waxy crudes with high water cut is below the gel point of waxy crudes,the gelled waxy oils adhere onto the wall of gathering pipelines leading to the contraction of the flow,which can be called the wall sticking of waxy crude oils.Therefore,the key to obtain the Boundary conditions for unheating gathering is to master the development of the waxy gel layer under the flow erosion.We analyzes the stress of the waxy gel layer under the flow erosion,and through the loop experiment,it has grasped the stripping and deformation form of the waxy gel,and established the prediction model of the Boundary conditions for unheating gathering,which provides theoretical support for the unheating gathering in the Xinmen and Mu17 waxy crude of Jilin oilfield.The following findings were made.Initially,the stress analysis of the waxy gel layer was systematically analyzed under the flow erosion.A schematic of flow loop for the erosion experiments were developed,and makes it clear that the resistance in the process of flow erosion is the yield stress to be overcome when the gel is continuously deformed and the adhesive stress to be overcome when the gel is stripped from the wall.Based on the study of failure modes of waxy gel in yield stress testing,the adhesive stress between the waxy gel and the pipe wall was measured by a rheometer with a smooth rotor system.The stress distribution of waxy gel layers was analyzed with the Ansys software.The results show that the maximal shear stress inside the waxy gels has 2 to 3 magnitudes higher than the wall shear stress applied by the fluid flow,which indicates the impulsive stress and the shear stress of the fluid flow commonly cause the sloughing of the waxy gels,rather than only the shear stress.Secondly,it was observed that initial temperature of "columnar waxy gel" of Xinmin and Mu17 crude oil is 32 ? under the steady-state operation of the pipeline(inner diameter 19 mm,flow rate 100 L/h or above).The stripping rule of waxy gel are as follow: It happens that waxy gel spread over the water once the shear stress of the fluid flow exceeds the cohesive strength of waxy gel and the oil temperature is higher than 32 ?.And it happens that the waxy gel is stripped from the pipe wall and pushed out of the pipe by the flow.And it happens that the waxy gel will not be stripped once the shear stress of the fluid flow is inferior to the adhesive strengthBased on the stripping rule of waxy gel,the experimental data of pressure drop during cooling operation of the pipeline were analyzed,and the rule of development of waxy gel with sticky wall was revealed.With the increase of the thickness of waxy gel,the shear stress of the fluid flow first overcome the adhesive stress,and the waxy gel is removed from the pipe wall.The "columnar waxy gel slug" is formed when the waxy gel is deposited,causing the pressure drop of the pipeline to rise rapidly.As the "columnar waxy gel slug" is pushed out of the pipe,the pressure drop drops rapidly.The test confirmed that "columnar waxy gel slug" go against unheating gathering,thus the initial temperature of "columnar waxy gel" should be used as the boundary temperature.It is concluded that the highest temperature for adhesion failure of Xinmin crude oil and Mu17 crude oil is 32 ? under the steady-state operation of the pipeline(inner diameter 19 mm,flow rate 100 L/h or above).It is concluded that the lower limit temperature of unheating gathering in Xinmin is 32 ?,which is 3?4 ? lower than gel point of crude oil.