Study On Rejection Water Control Along The Gathering System In Chunling Oilfield

Water flooding is the basis for the stable production of an old oilfield. A higher recovery rate and greater economic efficiency are the goal of the development of oilfields. Reaching the water quality standard is the key for water reinjection. Due to the presence of fouling ions, CO2, H2S, Fe2+, bacteria (especially sessile bacteria) and other water quality factors of instability, sewage transportation system could be resulted in corrosion, breeding of bacteria, increase of suspended solid content and quality deterioration of water along the path. Nowadays, the quantity of produced water is more than 80×104m3 per day in Shengli Oilfiled. Based on statistical result, more than 50% of the sewage water encounters secondary pollution. Low quality of injection water at the wellhead would result in the formation of plugging. This case becomes worse at the low permeability reservoir, where emulsification may enhance a blocking effect.Sewage water produced from oilfield has plenty of problems such as special physical and chemical characteristics, stable colloidal suspension particles, and the instability of water due to different ionic colloidal solution properties, corrosion, scale and bacteria. Our research is focused on the influence of these factors on water quality control in Chunliang Oilfield, a low permeability reservoir with a higher requirement of water quality, whose requirement is to achieve the level Al or A2. Our study has been conducted on the control of water quality along the whole process to ensure the injection water quality at wellhead.The variation of some key factors of the reinjection water was systematically studied, including the free bacteria, COD, sulfide, Fe2+, turbidity, suspended solids concentration and so on. The influence of sessile bacteria on water quality was clarified along the whole process. It was found that the free bacteria amount, COD value, total sulfide content, MLSS values and MLVSS values all present an increasing trend and followed by a decreasing trend as a function of time. Other factors, such as Fe2+ content and turbidity, show a monotonically increase with time. An on-line sampler for sessile bacteria was developed. A method for the detection and evaluation of sessile bacteria was also established. The results revealed the mature period of sessile bacteria and the film thickness increases with time variation at the internal wall of pipelines and equipments.Our study evaluated the stripping effect of bactericide to biofilm and sessile bacteria. Based on these researches, we established an evaluation method for the effectiveness of bactericide in stripping the bio-film and killing sessile bacteria.Our study also conducted stable quality control technology research of water in three blocks of Chunliang Oilfield, and they are Fanjia (sewage injection system), Gao 890 and Fan 147 (water system). Results show that for sewage injection system, the quality of water processed by the blocking membrane and ceramic membrane fine processing process can reach the Al level of water standard for injection into clasolite reservoirs. For water injection system, water quality along the process can remain stable by combined bactericidal and cleaning method. Therefore, the wellhead injection water quality can reach the standard, keeping an increase of the daily water injection rate.The establishment of the processing, transportation-reinjection of the whole chain of stable water quality control technology, plays an important role in guiding the water standard reinjection in oilfield.