尼日利亚边际油田合成基钻井液技术

Synthetic Base Drilling Fluid Technology for Marginal Oilfield in Nigeria

尼日利亚边际油田地层复杂,软泥岩水敏性极强、硬脆性泥岩坍塌掉块严重,且所钻井均为斜井。S5井使用的5%KCl聚合物钻井液无法抑制造浆性极强的软泥岩地层水化膨胀,硬脆性泥岩裂隙、层理发育,钻井过程中多次出现缩径阻卡、井眼坍塌、卡钻等复杂情况。根据地层特点,SIPEC使用合成基钻井液,通过添加油、主乳化剂、辅乳化剂、润湿剂、生石灰、增黏剂等处理剂、保持钻井液电稳定性大于400 V、油水比大于70∶30、黏度大于70s、钻井液API滤失量为0、高温高压滤失量小于3 mL、钻井液密度为1.3 g/cm3和使用强化固控等技术措施。保证钻井液性能稳定和井下安全,并采取随钻堵漏、优化性能、钻井液回收等措施降低了钻井液消耗,降低合成基钻井液的使用成本。在随后的S6井钻井施工中,使用合成基钻井液效果良好,保证了复杂井段的井下安全,提高了钻井速度,钻井周期由128 d下降到36 d。

Drilling deviated wells in water sensitive formations in the marginal oilfield in Nigeria frequently encountered downhole troubles because of the caving and sloughing of the mudstone rocks.For example,in well S5,a polymer drilling fluid containing 5%KCl cannot inhibit the hydration and swelling of the mud-making formation and the disintegration of the brittle mudstones.Tight hole,sloughing and pipe sticking were frequently encountered.Based on the analyses of the characteristics of the formations,a synthetic base drilling fluid was used in this area.The properties of this drilling fluid were as follows: emulsion stability ≥ 400 V,O/W ≥ 70∶30,FV> 70 sec,FLAPI = 0,FLHTHP < 3 mL,and the mud density was 1.3 g/cm3.Solids control was strengthened during drilling.Measures were taken to minimize the drilling fluid cost.This synthetic based drilling fluid was used in well S6,and drilling period was reduced from 128 d to 36 d.