一种低土相高密度抗钙钻井液体系

A Calcium Tolerant High Density Low Clay Drilling Fluid

土库曼斯坦阿姆河右岸区块地层基莫利阶为一套盐岩及石膏岩,且含有高压盐水层,在钻进该井段时,高密度钻井液易被侵入的钙镁污染,导致钻井液的流变性、滤失量等性能发生剧烈变化,流变性与沉降稳定性更加难以平衡,易导致复杂情况发生。针对现场地层情况,研究开发了一种低土相高密度抗钙钻井液体系D-ULTRACAL,通过使用新型增黏降滤失剂DSP-1,减少膨润土的加量,提高了钻井液的抗钙能力,并保持较低的滤失量;应用钻井液密度为2.0 g/cm^3,以防止井涌,稳定井壁;钻井液含有浓度接近饱和的氯化钠,可以抑制盐膏层的溶解。该体系抗温达150℃,API滤失量小于3.0 mL,高温高压滤失量小于15.0 mL;抑制性强,与自来水相比,岩屑回收率提高率达113.7%,岩心膨胀降低率达80.5%;抗钙离子污染能力达4 936 mg/L。在土库曼斯坦阿姆河右岸区块基尔桑气田Gir-24D井的现场试验表明,该钻井液体系在钻巨厚盐膏层特别是厚石膏层时具备优异的流变性能和滤失性能,现场钻井过程顺利。

The formation rocks of the Kimmeridgian stage on the right bank of the Amu Darya River, Turkmenistan, are halite and gypsum stone. High density drilling fluids used to drill this formation have always been contaminated by calcium and magnesium from the high pressure formation water, resulting in poor mud rheology and high filtration rate. The deteriorated mud rheology and filtration performance in turn resulted in other downhole troubles. A calcium tolerant high density low clay drilling fluid,D-ULTRACAL was developed to deal with these problems. A filter loss reducer, DSP-1, was used in the drilling fluid. DSP-1 can increase the viscosity of the drilling fluid, in this way reducing the clay content, improving the calcium tolerance and minimizing the filter loss of the drilling fluid. The density of the drilling fluid was 2.0 g/cm^3, sufficient to prevent well kick and to protect the borehole wall from collapsing. The drilling fluid had salt content almost to saturation to minimize the dissolution of the salt and gypsum rocks. The properties of the drilling fluid remained stable at temperatures up to 150 ℃, and the filtration rate was only slightly affected by high temperature aging. On a hot rolling test, the percent recovery of shale cuttings reached 113.7%, and on a shale core swelling test, the percent reduction in the expansion of shale cores was 80.5%, indicating the strong inhibitive capacity of the drilling fluid. Calcium tolerance of the drilling fluid was 4 936 mg/L. This drilling fluid has been used to drill the well Gir-24 D,which is located in the Girsan gas field, right bank of the Amu Darya River, Turkmenistan, and the thick salt and gypsum rock formations were successfully penetrated with no downhole troubles.