西非L-2000区块巨厚盐膏层钻井液技术

Drilling Fluid Technology for Thick Gypsum Salt Layer in West Africa Block L-2000

西非L-2000区块是中国石化在海外的重点勘探区块,埃詹加组是一套巨厚盐膏层,最大厚度达到1 226 m。前期施工井在埃詹加组均出现过缩径、卡钻、划眼困难、测井和下套管遇阻等井下复杂情况,其中2口井造成工程报废。对巨厚盐膏层钻井液技术难点进行了分析,制定了针对性技术对策。通过主处理剂优选,在原聚合物饱和盐水钻井液的基础上,开发了复合离子欠饱和盐水钻井液配方。室内实验表明,复合离子欠饱和盐水钻井液具有良好的沉降稳定性、抗钙侵、抗劣质土污染能力和防塌抑制性,根据其特点,制定了钻井液现场维护措施。LT-1井和LT-2井的应用表明,复合离子欠饱和盐水钻井液现场维护处理简单、性能稳定,盐膏层段井径规则,无缩径、卡钻复杂情况发生,平均井径扩大率分别为17.8%和12.5%。复合离子欠饱和盐水钻井液体系是适合该区块巨厚盐膏层钻井施工的成功钻井液体系。

The maximum thickness of Ezanga formation in West Africa block L-2000 is 1 226 m which is one of the key exploration blocks in the overseas for SINOPEC. There were many complexes when drilling in Ezanga formation such as tight-hole, sticking, reaming difficulties, logging and casing running blocking, and two wells were abandoned because the complexes. The corresponding technical measure was made after analyzing the drilling fluid technology difficulty of the thick Gypsum Salt Layer. On the basis of studying the original polymer saturated salt wa- ter drilling fluid, the compound ion under-saturated salt drilling fluid formula was developed after selecting the main agents. Evaluating test showed that the compound ion under-saturated salt drilling fluid has good characters such as sedimentation stability, resistance to calcium contamination, bad clay pollution and inhibition, The drilling fluid maintenance measures for the field application of the compound ion under-saturated salt drilling fluid was made ac- cording to its characteristics. The compound ion under-saturated salt drilling fluid was used in well LT-1 and well LT-2, which showed that the maintenance process was simple and the performance was stable. The two wells had regular and consistent borehole gauge and was without sticking complex case, the average hole enlargement rate were 17.8% and 12. 5% respectively. The compound ion under-saturated salt drilling fluid was appropriate for the thick salt-gypsum layer of Gabon Block L.