| In the development process of the oil and gas fields, there generally exists scale deposit in production systems, especially when water production increases in the late development. Wellbore scaling will lead to that the decrease of wellbore flow area, and the decline of fluid transportation efficiency, may also lead to well bore corrosion perforation or even out of use, seriously affecting the oil and gas production safety. In addition, frequent work over will spend a lot of time, manpower, financial and material resources. So far, the oil field pipeline scaling has been studied by a lot of people, but less for the gas field production pipeline scaling. Depending on the field practice of Shunan gas field of Petro China Southwest Oil and Gas Field Company (commonly abbreviated to Shunan gas field) the paper analyzed gas production wellbore scaling mechanism and scaling tendency, studied the anti-scaling measures, and proposed anti-scaling technology.(1) Jing26well, Tong18well, Ful well, He8well and H1well which are of typical scaling characteristics and can reflect the unique feature of Shunan gas field were selectedas object of study, extracting water samples and scale samples, in accordance with the regulations of Oil And Gas Fields Water Analysis Method (SY/T5523-2000), analyzing chemical composition by means of chemical titration and X-ray diffraction spectroscopy detection, confirming that the water quality in Shunan gas field is belong to CaCl2water type. and finally proving that, scale forming ions in the gas field water mainly include Ca2+Mg2+. Sr2+, Ba2+, HCO3-and SO42-, the gas field, the main composition in scale sample are of CaCO3, CaSO4, MgCO3, SrCO3, BaSO4and other fungi metabolic product, etc., in which the proportion of CaCO3scale is the highest.(2) By means of analyzing and studying the geological features, development programs, ion composition and process conditions of recalculated water in the Shunan gas field, the scaling tendency was predicted in accordance with the saturated index formula of CaCO3scale commonly applied in oil and gas fields in Predication Of Oil Field Water Scaling Tendency (SY/T0600-1997), adopted welibore scaling tendency of gas production well was analyzed by adopting using gas-liquid two-phase flow model and gas single-phase flow model respectively and the scaling tendency predicted with the two models are consistent, which indicated that formation of CaCO3scale is inevitable under the wellbore working environment of the gas well, and the scaling tendency increases with increasing temperature, consistent with theoretical speculation and field practice; meanwhile which also informed that the single-phase scaling forecasting model can be used to predict the scaling tendency of the wellbore of gas well.(3) The model predicting maximum amount of scale buildup of CaCO3appeared in gas well wellbore was established according to prediction formula for maximum amount of scale build up of CaCO3scale. By simulating, it was found that the position with largest amount of scale build up with in wellbore is within the range of500m from the well bottom, in line with the actual situation providing a reference for targeted removal of scale.(4) It is focused on the study of the chemical scale measures after comparative analysis of a variety of anti-scaling method, the proportion of CaCO3and CaSO4scale in the scaling product of Shunan gas field is the largest, so five kinds of single scale inhibitor of CaCO3scale such as sodium polyacrylate (PAAS), Amino Trimethylene Phosphon-ic Acid (ATMP),1-Hydroxy Ethylidene-1,1-Diphosphonic Acid (HEDP), Ethylene Diamine Tetra (Methylene Phosphonic Acid) Sodium (EDTMPS), Hydrolyzed Polymaleic Anhy-dride (HPMA),which is of high efficiency preventing CaCO3scale and commonly applied in oil field, were selected to analyzed the anti-scaling action of these scale inhibitor on CaSO4in accordance with the orthogonal experiment analysis. Through a ex-perimental study in the laboratory, three high efficiency scale inhibitors preventing CaSO4scale were selected from these five CaCO3scale inhibitors and, formula were formed by compounding the two agent among three, and then the formula proportion were changed and optimized. Experimental results show that the antiscale effect of antiscaling comp-ound is superior to a single dose, antiscale effect of some formula can reach up to more than80%, and have the good application value, but the formula should be adjust basedon different wellhead water samples.(5) For a typical gas well water samples, in addition to the study of the above described liquid anti-scaling method, the solid anti-scaling method was also studied. Solid anti-scaling block that is of good effect for corrosion and scale control was manufactured through experiment, finding carrier material of anti-scaling block suit for Shunan gas field, the optimum ratio of scale inhibitor and corrosion inhibitor. The test results showed that anti-scaling block produced with vinyl alcohol (PVA1799)as the carrier, sodium polyacrylate (PAAS) and benzotriazole (BTA) as for scale inhibitors and corrosion inhibitors respectively can reach the efficiency of control scale of more than80%, the efficiency of corrosion control of57%, with a strong practicability. Therefore, the anti-scaling block is a promising anti-scaling agent of gas field production, but its overall performance is to be further improved.(6) Many factors affect the wellbore scaling, including both composition of gas field water and reinjection process and operating conditions.For this, In order to further improve the scaling effect, the following process measures also were put forward, which include reasonable selection of reinjection well of gas field water, attention paid to compatibility of the reinjection water and formation, measures to reduce the injection water temperature and to improve reinjection water flow rate and pressure, the pretreatmentof the reinjection water on the ground surface(removal of solid impurities and hydrogen sulfide, disinfection) and acid cleaning the wellbore for scale control. |
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