ZQ2井盐膏层高密度欠饱和盐水聚磺钻井液技术

ZQ2是库车凹陷秋里塔格构造中秋2号构造的一口预探井，吉迪克组～库姆格列木群泥岩段（N1j2 ～ E_1-2km1）盐膏层埋藏深度在4545～5827 m，地层特性膏盐层段长、石膏含量高、压力系数高、盐间软泥岩欠压实高含泥质高含水与软黏特性、φ333.375 mm大尺寸井眼，原设计为油基钻井液，后更改为水基钻井液，且井深结构更改为高低压层套打，对水基钻井液技术提出了较高要求。针对地层特性通过改变传统钻井液体系思路引入烯丙基磺酸钠四元共聚物降滤失剂MYK、改性植物胶包被抑制剂NXX、国内首次在欠饱和盐水体系中引入有机盐Weigh2对传统的欠饱和盐水磺化钻井液进行改造升级为聚磺高密度欠饱和盐水钻井液，在实钻过程中表现出包被抑制性强、抗盐膏污染能力强、性能稳定、维护简单、岩屑代表性强，流变性控制优于邻井欠饱和盐水磺化钻井液，在ZQ2井该段盐膏层取得了良好效果，解决了传统欠饱和盐水磺化体系因使用稀释剂致强分散、强依赖性而出现“加～放～加、增黏～降黏～增黏”难题，实现了该层位盐膏层及软泥岩安全快速钻进、井壁稳定、井下安全，电测、下套管一次性成功，为该区块优化井身结构奠定了基础。 

A High Density Undersaturated Saltwater Drilling Fluid for Salt and Gypsum Drilling in Well ZQ2

Well ZQ2 is an exploratory well located at the Qiu-2 substructure of the Qiulitage Structure in the Kuche sag. This well penetrated the mudstone Jidike Formation-Kumugeliemu Group (N1j2 -E_1-2km1) which are buried at depths from 4545 m to 5827 m. This section is characterized by long salt/gypsum formations, high content of gypsum, high formation pressure, soft mudstones embedded with salt and unconsolidated soft high argillaceous content high water content rocks. The diameter of the hole penetrating this section is φ333.375 mm. This section was previously designed to drill with oil base mud, and was then changed to water base mud. High-and low-pressure formations exist in the same interval. All these challenges demand more of the water base drilling fluid to be used. An undersaturated polymer sulfonate drilling fluid was prepared using a sodium polyallyl sulfonate filter loss reducer MYK, a modified plant gum encapsulating inhibitor NXX and an organic salt Weigh2 which was first used to improve the undersaturated sulfonate drilling fluid to high density undersaturated polymer sulfonate drilling fluid. This drilling fluid have shown itself strong inhibitive capacity, high resistance to salt and gypsum contamination, stable properties and simple maintenance of rheology. Drilled cuttings acquired by the mud loggers were accurately relevant to the formation being drilled. The rheology of this drilling fluid during drilling was also much easier to control than the rheology of the drilling fluids used nearby. Application of this drilling fluid in drilling the well ZQ2 was a success, without encountering problems encountered when using other undersaturated drilling fluids, such as the use of thinners which leads to "adding mud-dumping mud-adding mud again, viscosifying-thinning-viscosifying". Using this drilling fluid, the salt/gypsum formations were successfully and safely drilled through, borehole wall was stable during drilling, wireline logging and casing running were successful at the first try. This drilling fluid technology has provided the base for casing program optimization in the Kuche sag.