Paraffin Characteristics of Waxy Crude Oils in China and the Methods of Paraffin Removal and Inhibition

Abstract

Abstract The crude oil in which the wax content is more than 10% (w), nearly accounts for 90 percent of the total output of crudes in China. On the whole, for the waxy crudes in China, from eastern to western, the wax content in these crudes tends to decline and so does the pour point of these crudes. But for the eastern area in China, from the north to the south, there is an increasing tendency of wax content and pour point of the crudes. Crudes with the wax content less than 15% (w) and pour point below 25 C are such crudes as Turpan-Harni Basin, Tarim Basin, Shanganing Basin etc.; crudes with the wax content ranging from 15% to 25% (w), and pour point between 25 C to 35 C are such crudes as Daqin, Jilin, Dagang, Jidong, Huabei, Zhongyuan and Shengli etc. oilfields ; Crudes with wax content more than 25% (w) and pour point above 35 C are such crudes as Jiangsu, Nanyang, Baise etc. oilfields. Nevertheless, the above-mentioned regularities are not absolute. For example, the crude of Shenbei, Liaohe oilfield, contains wax up to 50% (w) and its pour point comes to 50 C or even higher, but it is a rare example. To compare the composition and structure of wax, although the wax content in the waxy crudes in eastern China is much more, the carbon-number (CN) of the wax is not very high, generally, in the range C13 -C40, the CN distribution of wax analysed by GC (Gas Chromatography), appears only one peak area, and the wax in its structure has some branch degree analysed by NMR (Nuclear Magnetic Resonance). while the crudes in western China, especially some crudes in Xinjiang area, such as Tuha (Turpan-Hami Basin), Taxinan, Huoyanshan crudes contain less wax content and have a lower pour point, but the CN of wax is relatively higher, the wax with CN in the range of C36-C70 nearly accounts for about 50% (w) of the total wax content. The CN distribution of the wax appears two peak areas on GC-photography (i.e. C 13 - C35 peak area and C36 - C70 peak area). The structure of the wax is nearly like that of pure normal alkane without any branch in its molecular chain. In accordance with different wax content, water cut and pour point of a crude, it is needed to adopt different paraffin removing and inhibiting techniques to obtain the best economic benefit. For the oil wells with water cut below 50% (w), wax content less than 30% (w) and CN distribution of the wax in the range C13 - C40, good efficiency can be obtained by using chemical removing and inhibiting techniques (such as liquid paraffin remover or solid state paraffin inhibitor); for the wells with water cut more than 50% (w), the magnetic paraffin-inhibiting technique is generally more economic to apply; For the wells with wax content more than 30% (w), and pour point higher than 40 C, whether more or less the water cut, the magnetic paraffin inhibiting technique is not a best choice, but the chemical paraffin remover and inhibitor or hot surfactive water (or hot oil) treatment or even thermochemical paraffin removing treatment should be adopted in this case; for the wells with high CN wax, both the magnetic and pure chemical paraffin removing techniques are all invalid, the best economical choice is to apply chemical paraffin inhibitor or glass (or coating) linking tubing paraffin-inhibiting technique. P. 33