低油水比水包油钻井液体系的研制及应用

DEVELOPMENT AND APPLICATION OF OIL-IN-WATER DRILLING FLUID SYSTEM WITH LOW OIL/WATER RATIO

磨溪气田嘉二段气藏具有典型的“高压、高渗、高含硫”特点，以往所钻的直井及水平井在 152．4mm小井眼井段使用聚磺钻井液密度一般为2．30～2．50g／cm^2，几乎每口井都出现多次滤饼粘附卡钻；另外该井段富含石膏及夹薄层岩盐对钻井液污染严重，流变性不好控制，钻井中常出现高泵压等问题。针对以上难题，从分析高密度条件下的粘卡原因及出现高泵压的流变性失控原因入手，研制了一种超高密度低油水比水包油钻井液体系，室内进行了产层岩样密封能力、滤饼表面油润湿性、抗膏盐污染等方面的评价，现场应用于磨005-H8井水平段钻井中取得了良好效果。表明该配方体系能较好地满足磨溪气田所钻井的需要，大幅度地降低了钻井扭矩和起下钻摩阻，能有效防止粘附卡钻和高泵压问题，具有高密度条件下流变性易控制、抗膏盐污染能力强、对泵橡胶件损害小、安全经济等优点。

The gas zones at Jia-2 formation in the Moxi gas field are characterized by high pressure,high permeability,and high H2S content.The polymer sulfonated drilling fluid was normally used to drill the φ152.4 mm interval of vertical or horizontal wells,with density ranging from 2.30 to 2.50 g/cm3.However,nearly in all those wells drilled there occurred differential sticking for more than once,and the drilling fluid was subject to contamination by the gypsum or thin inter-bedded rock salt,making rheology not easy to control,in addition to high pump pressure often resulted during drilling.Hence based on analysis of the causes of the sticking in high-density drilling fluid and the rheological causes of high pump pressure,a low oil/water ratio and oil-in-water drilling fluid system with extra-high density is developed.The sealing capability,oil wettability of filter cake,anti-gypsum capability of the rock samples of the payzone being studied have been evaluated in the lab.It has also been successfully used to drill the horizontal wellbore of the well Mo 005-H8.All demonstrate this system can be well used to satisfy the requirements of drilling in the Moxi gas field,largely decrease the torque during drilling and drill string drag during tripping,and effectively prevent differential sticking and high pump pressure problems.This system has advantages of easy rheological control when density is high,high capability to combat the gypsum contamination,little damage to pump elastomers,and being safe,and economically efficient.