Experimental investigation of sand production in moderately consolidated sandstones
LIU Wei, YAN Xinjiang, LIN Hai , ZHOU Bao , LIU Xiaogang , DENG Jingen
1 State Key Laboratory of Petroleum Resource & Prospecting, Beijing 102249, China 2 College of Petroleum Engineering, China University of Petroleum-Beijing, Beijing 102249, China 3 CNOOC Research Institute, Beijing 100028, China 4 CNOOC Limited, Tianjin Branch, Tianjin 300459, China 5 PetroChina Tarim Oilfield Company, Korla 841000, China 6 CNOOC Limited, Beijing 100010, China
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.
LIU Wei, YAN Xinjiang, LIN Hai, ZHOU Bao, LIU Xiaogang, DENG Jingen. Experimental investigation of sand production in moderately consolidated sandstones. Petroleum Science Bulletin, 2021, 01: 67-78.
