低密度无固相海水钻井液在南海西部D气田的应用

Application of Low Density Solids-free Seawater Drilling Fluid in D Gas Field in Western South China Sea

南海西部D气田目前在生产的浅层气藏,属上第三系莺歌海组地层,是中孔中渗的泥岩储层,该地层较复杂,钻进时易发生掉块、井塌、卡钻等井下复杂。在研究储层岩石性质及现有钻井液性能存在问题基础上,提出应提高体系的封堵性能以及抑制性能,措施为:在φ311.1 mm井段原PRG钻井液配方中增加VIS,降低滤液侵入速度,降低钻井液对于井壁的冲刷作用;降低PLUS的含量和增加PF-FLOTROL,降低黏度并增强降滤失性能;在φ215.9 mm井段原PRF钻井液配方中增加Greenseal,形成致密隔离层带,封堵微裂缝和孔喉,降低滤液渗透,延长井壁稳定时间;增加EZCARB的含量并且使用KCl加重,增加抑制性能。评价结果表明,PRG和PRF钻井液具有滤失量低(API滤失量为2.1 mL,高温高压滤失量约为4.3 mL)、流变性好、抑制性强(滚动回收率约为90%)和抗污染能力强(抗盐达10%,抗钙达2%)等特点。在D气田P3H井和D4H井的现场应用表明,使用PRG和PRF钻井液,有效抑制了泥包卡钻、井漏等井下复杂的发生,使用效果良好。

The shallow gas reservoir presently produced in the D gas field in western South China Sea is located in the Yinggehai formation of the Tertiary System,which is a medium porosity medium permeability mudstone reservoir.This formation has complex geological characteristics,and sloughing,borehole collapsing and pipe sticking have all been encountered during drilling operation in the past.Based on the studies on the rock properties of the reservoir and the problems associated with the drilling fluids it was concluded that the plugging and inhibitive capacity of the drilling fluids should be strengthened.That being said,the drilling fluid(PRG)previously used to drill the Ф311.1mm was treated with VIS to retard the invasion of mud filtrate into the formation and to minimize the erosion of drilling fluid to the borehole wall.The concentration of PLUS in the drilling fluid was reduced and PF-FLOTROL increased to reduce viscosity and filter loss.In the Ф215.9mm interval,the PRF mud was treated with Grreenseal to plug micro fractures and pore throats,and to retard the filtration of mud filtrate,thereby prolonging the time of borehole wall stability.Using more EZCARB and weighting the mud with KC1,the inhibitive capacity of the mud was improved.Evaluation experimental results showed that PRG and PRF muds had low filter loss(API filtration rate was 2.1mL and and HTHP filtration rate was4.3mL),good rheology,strong inhibitive capacity(shale cutogs recovety on hot rolling test was±90%) and excellent contemination resistance(salt resistance to10% and calcium resistance to2%).Application of the PRG and PRF drilling fluids on well P3H and D4H in D gas field showed that downhole troubles previously encountered,such as bit balling,pipe sticking and mud losses were successfully avoided.