中高密度粘弹性表面活性剂压裂液的研制与应用

Middle-to-High Density Viscoelastic Surfactant Fracturing Fluids: Preparation and Application

青海涩北气藏地层压力系数在1.3左右,盐敏性强,临界矿化度为8×104mg/L.针对该气藏及类似油气藏研制了中高密度(1.05～1.70 g/cm3)VES压裂液.讨论了VES压裂液的形成及破胶机理.压裂液密度由盐水提供,给出了盐水密度与无机盐种类、浓度关系式.所用表面活性剂是专门研制的,代号CFP-Ⅲ,在基本配方中用量15～40 g/L.密度1.30 g/cm3、CFP-Ⅲ浓度30 g/L的VES压裂液的性能如下:20℃下的流变性显示剪切变稀特性;在20～45℃粘度基本恒定,在45～90℃粘度随温度上升而增大,＞90℃后粘度下降,在110℃时为53 mPa·s,因此该VES压裂液可用于120℃地层;在20℃、170 s-1下剪切60分钟使粘度降低25%,继续剪切时粘度不变;加入0.5%多烃类处理剂时彻底破胶,破胶液粘度与盐水相当;对储层岩心渗透率的伤害率仅为6.08%～11.14%.使用该VES压裂液在涩北13口气井进行压裂防砂先导性试验,气井不出砂日产气量增加75%～180%;给出了一口井的施工参数曲线图.图7表1参6.

The Sebei gas reservoir in Qinghai is characterized by formation pressure coefficient - 1.3, strong salt sensibility and critical salinity 8× 10^4 mg/L. For use in this and similar reservoirs, a middle-to-high density, of 1.05--1.70 g/cm^3, VES fracturing fluid （FF） is developed. The principles of formation and breakdown of VESFFare presented. The density of VESFF is boosted in terms of salt water, for which a relationship between density and class and concentration of inorganic salts is presented. A surfactant, CFP- Ⅲ, is specially developed and used in amount of 15--40 g/L in basic formulations. For a VESFF of density 1.30 g/cm^3 and CFP-Ⅲ concentration 40 g/L, the properties are dipicted by following data： the rheologic behavior at 20℃ is of shearing-thinning type; the viscosity does not change practically at 20--45℃, raises with raising temperature at 45--90℃ and drops down at 〉90℃, being of 52 mPa·s at 110℃ therefore this systena of VESFFs can be used at temperatures up to 120℃ ; viscosity is reduced by 25% when shearing at 20℃ and 170 1/s over 1 hr and kept at this level at shearing further; with 0.5 % multihydrocarbon treating agent added, the VESFF breaks down thoroughly to give a liquor as thin as salt water; a damage in range 6.08--11.14 % is observed to reservoir core permeability. With this VESFF used in pilots on fracturing/sand control in 13 gas wells of Sebei reservoir, the daily gas production per well is increased by 75--180% without any sand production. The curves of technologic parameters of fracturing/sand control ooeration are Riven for one tvoical well.