摘要
油气井出砂是油气藏开采面临的一个重要的挑战,给正常生产带来极大的影响。在各类砂岩储层中,具有一定胶结强度的中等固结砂岩出砂机理及出砂规律尚不清楚,制约了这类储层的出砂临界条件和出砂速率准确预测。本文利用一种中等固结砂岩露头,在单、三轴实验的基础上,设计开展了不同变形破坏阶段的卸载实验及应力和流体渗流共同作用下的出砂模拟物理实验,揭示了中等固结砂岩的出砂机理、出砂规律以及产出物特征。研究结果表明:中等固结砂岩的出砂临界条件是孔眼周围岩石在应力集中作用下进入残余变形阶段,此时孔眼周围形成宏观剪切裂缝,裂缝面相对滑移错动破坏裂缝面附近的颗粒胶结,形成可供产出的离散砂,剪切裂缝的扩展连通产生尺寸较大的掉块,与裂缝面上的离散砂共同为出砂提供物质来源。出砂量与孔眼周围应力集中造成的破坏范围大小成正比。流体拖曳力的作用是将剪切破裂形成的固相产物运移产出,对最终的出砂量影响较小,只影响出砂速率。粒度测试结果表明,中等固结砂岩产出砂中存在由多个砂粒聚集在一起的相对直径较大的颗粒,产出砂粒度中值比原始地层砂大2~3倍,在防砂参数设计优化时应予考虑。本文的研究结果能够为构建中等固结砂岩出砂定量预测模型以及防砂参数优化设计提供依据。
Sand production has long been a challenging problem which may cause a series of problems for petroleum production.Among various types of sandstones,sand production from moderately consolidated sandstones is still less understood in terms of the mechanism and the influencing factors.This greatly limits the precise prediction of the critical sand production conditions and the sand production rate.In this paper,with a moderately consolidated sandstone,in addition to the conventional uniaxial and tri-axial compression tests,unloading tests after loading to different deformation stages and sand production,physical model experiments under different stress and fluid flow conditions have been conducted to investigate the mechanism of sanding as well as the characteristics of the produced sands from the moderately consolidated sandstone.The results show that the necessary condition for sand production from moderately consolidated sandstones is that the rock around the wellbore or perforation deforms into the residual plastic deformation stage under the effect of stress concentration,leading to localized shear fractures around the wellbore or perforation.Discrete sands are generated during the formation of shear fractures due to destruction of cementation of the grains on the shear fracture,which is further enhanced by relative slippage of the fracture surfaces.Intersection of conjugate shear fractures near the surface of wellbore or perforation will also generate debris of relatively large size.Both these discrete sands and debris form the material source of sand production.The quantity of produced solids has been observed to be proportional to the confining stress applied at the external surface of the samples.It is also demonstrated that fluid flow only serves to transport the produced solids which have been generated from failure of the rock around the wellbore or perforation,thus the flow rate is of marginal effect on the quantity of produced solids,although it indeed influences the rate of the production of solids.It has also been observed that many of the sand particles produced from the moderately consolidated sandstone are composed of several bonded sand grains,thus the mean particle size of the produced sands is 2~3 times larger than that of the virgin sands of the moderately consolidated sandstones.This needs to be considered in the sand proof design.The results in this paper are anticipated to be beneficial for establishing models for quantitative prediction of sand production from moderately consolidated sandstone as well as for optimization of the sand proof design.
作者
刘伟
闫新江
林海
周宝
刘小刚
邓金根
LIU Wei;YAN Xinjiang;LIN Hai;ZHOU Bao;LIU Xiaogang;DENG Jingen(State Key Laboratory of Petroleum Resource&Prospecting,Beijing 102249,China;College of Petroleum Engineering,China University of Petroleum-Beijing,Beijing 102249,China;CNOOC Research Institute,Beijing 100028,China;CNOOC Limited,Tianjin Branch,Tianjin 300459,China;PetroChina Tarim Oilfield Company,Korla 841000,China;CNOOC Limited,Beijing 100010,China)
出处
《石油科学通报》
2021年第1期67-78,共12页
Petroleum Science Bulletin
基金
国家自然科学基金面上项目(52074313)资助。
关键词
中等固结砂岩
出砂模拟实验
出砂机理
出砂特征
出砂临界条件
moderately consolidated sandstones
sand production experiment
sanding mechanism
sanding characteristic
sanding critical condition
