复合盐膏层井眼缩径机理与对策分析

Borehole shrinkage mechanism and countermeasure analysis of composite salt-gypsum layer

林海 邓金根 许杰 谢涛 刘海龙2

中国石油大学（北京）油气资源与探测国家重点实验室，北京 102249 中海石油（中国）有限公司天津分公司海洋石油高效开发国家重点实验室，天津 300459

State Key Laboratory of Petroleum Resources and Prospecting, China University of Petroleum, Beijing 102249, China State Key Laboratory Offshore Oil Exploitation, Tianjin Branch of CNOOC Ltd., Tianjin 300459, China

目前，在非均匀地应力和考虑盐膏层与软泥岩互层蠕变相互影响的条件下，对控制复合盐膏层井眼缩径的合理钻井液密度的确定方法研究较少。为此，文中以Buzurgan油田复合盐膏层井眼缩径问题为例，在岩石力学实验的基础上，建立了盐层￣软泥岩￣盐层的三维FLAC3D复合盐膏层模型，并编制了控制复合盐膏层井眼缩径安全钻井密度图版。结果表明：在相同钻井液密度条件下，最小水平地应力方位井眼缩径率高于最大水平地应力方位井眼，而软泥岩夹层井眼缩径速率高于盐岩地层井眼，软泥岩蠕变是造成Buzurgan油田复合盐膏层井眼缩径的主要原因；为控制井眼缩径，钻井液密度应取2.35 g/cm3；控制复合盐膏层井眼缩径的同时，要提高钻井液的矿化度、降滤失性和封堵性，抑制软泥岩的蠕变。研究成果复合盐膏层的安全钻进提供了技术支撑。

Current research methods determining the reasonable drilling fluid density that controlls hole shrinkage of composite salt-gypsum rock seldom consider non-uniform in-situ stress and mutual influence between salt-gypsum layer and soft mudstone creep. Taking the composite salt-gypsum layer of Buzurgan Oilfield for example, a three-dimensional FLAC3D model of composite salt-gypsum layer was established to make hole shrinkage simulation in composite salt-gypsum layer on the basis of rock mechanics experiments, and the safe drilling density chart was obtained to control hole shrinkage in composite salt-gypsum layer. Results show that borehole shrinkage rate of soft mudstone in gypsum intercalation is higher than that in the salt-gypsum layer under the same condition of drilling fluid density, and soft mudstone creep is the main reason that causes borehole shrinkage of composite salt-gypsum layer for Buzurgan Oilfield. Shrinkage rate of level minimum in-situ stress orientation is higher than that of the horizontal maximum in-situ stress orientation. In order to control borehole shrinkage of composite salt-gypsum layer for Buzurgan Oilfield, drilling fluid density should be not less than 2.35 g/cm3. In addition, it is necessary to improve drilling fluid mineralization, filtrate reduction and seal property to inhibit the mudstone creep. Research results will provide technical support to solve borehole shrinkage of composite salt-gypsum layer.

10.6056/dkyqt201806022