陕北富县探区天然气藏钻井液屏蔽暂堵技术

Shielding Temporary Bridging Drilling Fluid for the Natural Gas Reservoir in Fuxian Exploration Area of Shanbei

陕北富县探区上古生界储层属低孔、低渗的致密储层,下古生界主要储集空间为溶蚀孔洞和裂缝,孔洞多为1～3 mm的小孔,裂缝宽度为0.2～7.0 mm,油气主要聚集在裂缝中.优选出了由复合暂堵剂CXD、憎水性屏蔽剂DYC和表面活性剂ABA组成的屏蔽暂堵配方,其中CXD具有架桥作用并对裂缝性储层有独特暂堵效果,DYC有浊点效应、能在井壁上快速形成阻止滤液侵入的油膜,ABA能减少水锁损害.加入暂堵剂后的钻井完井液,抑制性增强,页岩回收率在90%以上;高温高压滤失量降低,滤饼薄而韧、光滑;岩心静态渗透率恢复值大于90%;滤饼摩阻系数降低.富古6井通过使用该完井液,堵塞比和表皮系数都在轻微污染范围内,井径扩大率比其它井有不同程度的降低,表明优选出的屏蔽暂堵钻井完井液,能很好地保护陕北探区天然气藏.

Neopalaeozoic formation of Fuxian Exploration Area in Shanbei was low porosity and permeability and tight.Major reservoir pore spaces in Down-Palaeozoic were emposieus with 1～3 mm by diameter and fractures with 0.2~7.0 mm by width which were main accumulation areas of oil and gas.The shielding temporary bridging formulation was optimized in which the composite temporary bridging agent of CXD could provide unique temporary bridging effect,the hydrophobic shielding agent of DYC with turbidity effect could short time form the oil film on the borehole face to prevent filtrates invasion and the surfactant of ABA could decrease formation damages resulted from the water block effect.The drilling and completion fluids containing temporary agents presented improved inhibition and shale recovery ratio was more than 90%.And also,it had little high temperature and high pressure filtrate and the mudcake was thin,flexible, smooth and low friction resistance.The recovery ratio of permeability was more than 90% obtained by the static core damage test.The data of damage ratio and skin factor from Fugu-6 well proved a slight pollution acquired.A minor borehole enlargement ratio was also obtained through caliper log.It was proved that the shielding temporary bridging drilling and completion fluid optimized could effectively prevent the natural gas reservoir in exploration area of Shanbei from damage.