Study On Paraffin Deposit Mechanism Of Oil Well Bore And Technology For Paraffin Removal&Control

The reservoirs, well bores and surface gathering lines all may be affected byparaffin deposition during the production process of crude oil. The paraffin depositionon the well bore leads to the conduit blockage of oil flow and further severely interfereswith the normal production of oil wells, resulting in the reduction of the oil wellproduction. However, once “paraffin blockage” takes shape, it results in severalproductive faults such as paraffin jam of sucker-rod pumping system, directly leading tooff production of oil well. This thesis takes paraffin deposition of oil well bore asstudy object and researches into it and corresponding paraffin removal and controltechnology through the combination of experimental study, theoretical calculation,numerical simulation and field test on the basis of thermodynamics, fluid mechanics,pattern recognition and multiple attribute decision making method. And the mainresearch results and conclusions are as follows:①Based on the analysis of paraffin basic features, this thesis comprehensivelyconsiders the effects from heat conduction, convection and heat radiation of well boreand establishes the specific mathematical model for transient temperature prediction ofthe pumping well bore equipped with sucker-rod pump; and it is found that the wellbores in the certain regions may have paraffin deposition for long well section throughthe transient temperature prediction above mentioned integrating test of flow behaviorin well bore when the relevant temperatures stay at the freezing point and paraffinprecipitation point, moreover, this research conclusion conforming to the field practice;meanwhile, the research indicates the changes of conditions including moisture content,oil temperature, flow rate and temperature difference of tubing wall etc. will directlyresult in the change of the targeted well section with paraffin deposition,while thechange of well section with paraffin deposition is affected by some factors such as oilproduction, tubing size, thermal conductivity, surface roughness and flowing productiontime which indirectly change well bore temperature.②The author applied the FLUENT Software to perform the simulation analysison the flow fields of the sucker-rod collar and the subsurface pump for the severeparaffin deposition of the cross-section mutation part in the oil production system; it isfound through the velocity vector and nephogram of crude oil in the sucker-rod collarand the subsurface pump under various oil production that severe paraffin deposition generally occur at sucker-rod collar or around standing valve and traveling valve andthis problem cannot be effectively settled only by increasing yield and raising the flowrate; thus, the relevant measures for paraffin removal and control shall be taken toprevent paraffin deposition.③Based on the mechanical analysis of sucker-rod micro unit in the vertical welland the directional well, this thesis established the mathematic model for fault diagnosisof the sucker-rod pumping system or accurately identifies the root causes and relevantsolution through finite difference method and precise integration; furthermore, on thebasis of the following procedures, the author realized the intelligent diagnosis on theparaffin deposition faults of sucker-rod pumping system respectively by use ofcross-validation (K-CV), genetic algorithm (GA), particle swarm optimization (POS)and parameters of support vector machine (SVM).④This thesis established the optimization model for well paraffin removal&control on the basis of multiple attribute decision making method such as entropy theory,fuzzy analytic hierarchy process, technique for order preference by similarity to idealsolution (TOPSIS), and grey correlation method etc; and this model takes new relativecloseness coefficient instead of Euclidean distance and grey correlation and this modelfeatures clearer physical meanings and shows dual benchmarks; in addition, the applicationindicates that the above-mentioned model based on the multiple attribute decision makingmethod can further improve the objectiveness and comprehensiveness of problem analysis,and this model can realize the exploitation of inherent law in the original data to certainextent. Therefore, it presents certain value of promotion and application.⑤The author developed paraffin remover and inhibitor TH-1for new oil wellswith the various components including surfactant, organic solvent, polymer materialsand mutual solvent etc; and aiming at the demands of field test, the author establishedthe method for determining the interval dosing cycle on the basis of the extension theory,accurately identifying the working conditions in accordance with the parameter changes,thereby, reasonably defining the dosing cycle. In addition, thelabassessment tests andfield tests indicate that the paraffin remover and inhibitor TH-1for new oil wells caneffectively solve the paraffin deposition of oil well bore at site.