地層出砂是指地層在鑽井過程及生產過程中，井壁周圍岩石受到鑽井設備擾動或是過度的壓力變化，超過岩石所能承受限制而造成岩石崩壞，崩壞物質隨地層流體一併進入井內的現象。
在地層出砂現象中，由於其中所包含的物質多為高硬度二氧化矽，在流動過程中會不斷衝擊生產設備，導致磨損及設備沖蝕。若地層砂持續累積在井內，將造成地層孔道及井內空間的阻塞影響油氣生產。
為防止地層出砂所導致的危害，在生產過程中可採用防砂措施避免出砂。防砂措施主要分為機械防砂、化學膠固及壓力控制。機械防砂多為安裝防砂篩管，利用篩孔防止地層砂進入井內。化學膠固為使用藥劑使井壁產生阻隔層強化井壁以避免出砂。壓力控制則是以臨界出砂壓力為標準，以不出砂條件下的生產壓力進行生產。壓力控制法較前兩項防砂措施不受砂粒徑影響，於較細的地層砂同樣有其效果。但由於壓力控制所採用的臨界出砂壓力是以地層原始狀態為基準，未考慮地層在受到破壞後，地層與原始狀態之差異。因此本研究以臨界出砂壓力為基礎，加上不同地層破壞程度影響，計算求得後續臨界壓力。
此後續臨界壓力為表示一地層在遭受破壞歷經地層出砂後，該地層在此狀態後，避免再度出砂所面臨的臨界出砂壓力限制。此壓力相較原始臨界出砂壓力更低，地層可以較大壓力差進行生產，具有較高之經濟效益。
本研究可獲致結論如下：(1) 地層的臨界出砂壓力會因地層破壞程度(累積出砂量)不同而有所變化。臨界出砂壓力會隨累積砂量變化而逐漸降低而逐漸趨向穩定值。(2) 當累積砂量增加，地層塑性區範圍也隨之擴大，地層砂所需經過的距離也較長，出砂難度上升。(3) 本研究所得之後續臨界出砂壓力應更能表示地層出砂所需面臨的生產壓力限制，有助於油氣生產達到更佳之經濟效益。

The purpose of this study is to modify an equation of sand production to a different form to predict the critical pressure. To use this prediction equation, we need to input some parameters from field data. Because some data of plastic zone cannot be directly obtained, we use the sensitivity analysis to assume these parameters. After entering these data, we need to set some bottomhole pressure and sand production volume values, which are not real values from field data. Each sand production volume can be combined with different bottomhole pressures to determine the pressure with sand production rate equal to zero. This pressure is the critical pressure without sand production. If we use this critical pressure to produce oil or gas, this well will not have the problem of sand production.
In this study the following conclusions can be drawn: (1) Due to differences in formation damage, the critical pressure without sand production will change immediately. The critical pressure will decline and reach a stable value, if sand accumulates to a sufficient volume. (2)With the accumulation of sand, the difficulty of sand production will increase. If we apply a constant pressure, which can cause sand production, with increases in the accumulation of sand, the rate of sand production may decrease or stop. In this case, sand production does not persist.

1. Bratli, R.K. and Risnes, R., “Stability and failure of sand arches,” Society of Petroleum Engineers Journal, Vol. 21, pp. 236-248, 1981.
2. Coates, G.R. and Denoo, S.A., “Mechanical Properties Program Using Borehole Analysis and Mohr’s Circle,” SPWLA Twenty-Second Annual Logging Symposium held in Mexico City, June 23-26, 1981.
3. Dusseault, M.B. and Morgenstern, N.R., “Shear Strength of Athabasca Oil Sands,” Canadian Geotechnical Journal, Vol. 15, pp. 216-238, 1978.
4. Geilikman, M.B. and Dusseault, M.B., “Fluid rate enhancement from massive sand production in heavy-oil reservoirs,” Journal of Petroleum Science and Engineering, Vol. 17, pp. 5-18, 1997.
5. Geilikman, M.B., Dusseault, M.B., and Dullien, F.A.L., “Sand production as a viscoplastic granular flow,” SPE Formation Damage Control Symposium held in Lafayette, Louisiana, U.S.A., February 7-10, 1994.
6. Geilikman, M.B., Dusseault, M.B., and Dullien, F.A.L., “Fluid production enhancement by exploiting sand production.” SPE/DOE Improved Oil Recovery Symposium held in Tulsa, Oklahoma, U.S.A., April 17-20, 1994.
7. Hossein Rahmati, Mahshid Jafarpour, Saman Azadbakht, Alireza Nouri, Hans Vaziri, Dave Chan, and Yuxing Xiao, “Review of Sand Production Prediction Models,” Journal of Petroleum Engineering, 2013.
8. Katona, M.G., “Evaluation of viscoplastic cap model,” J. Geotech. Eng. of ASCE, No. 8, pp. 1106-1125, 1984.
9. Perkins, T.K., and Weingarten, J.S., “Stability and failure of spherical cavities in unconsolidated sand and weakly consolidated rock,” SPE Annual Technical Conference and Exhibition held in Houston, Texas, U.S.A., October 2-5, 1988.
10. Risnes, R., Bratli, R.K. and Horsrud, P., “Sand stresses around a wellbore,” Society of Petroleum Engineers Journal, Vol. 22, pp. 883-898, 1982.
11. Tixier, M.P., Loveless, G.W. and Anderson, R.D., “Estimation of formation strength from mechanical-properties log,” Journal of Petroleum Technology, pp. 283-293, 1975.
12. van den Hoek, P.J. (2001), “Prediction of different types of cavity failure using bifurcation theory,” The 38th U.S. Symposium on Rock Mechanics held in Washington DC, U.S.A., July 7-10, 2001.
13. van den Hoek, P.J. and Geilikman, M.B., “Prediction of Sand Production Rate in Oil and Gas Reservoirs,” SPE Annual Technical Conference and Exhibition held in Denver, Colorado, U.S.A., October 5-8, 2003.
14. van den Hoek, P.J., Hertogh, GH.M.M., A.P. Kooijman, de Bree, P., Kenter, C.J., and Papamichos, E., “A new concept of sand production prediction: theory and laboratory concepts,” SPE Drilling & Completions Journal, Vol. 15, pp. 261-273, 2000.
15. van den Hoek, P.J., Kooijman, A.P., de Bree, P., Kenter, C.J., Zheng, Z., and Khodaverdian, M., “Horizontal wellbore stability and sand production in weakly consolidated sandstones,” SPE Drilling & Completions Journal, Vol. 15, pp. 274-283, 2000.
16. Vyalov, S.S., “Rheological fundamentals of soil mechanics,” Developments in Geotechnical Engineering, Elsevier Science Publishing Company, Amsterdam, 1986.
17. Wang Huan-ling, Xu Wei-ya and Yang Sheng-qi, “Experimental investigation on permeability evolution law during course of deformation and failure of rock specimen,” Rock and Soil Mechanics, vol. 27, 2006.
18. Weingarten, J.S. and Perkins, T.K., “Prediction of Sand Production in Gas Wells: Method and Gulf of Mexico Case Studies,” Technical Conference and Exhibition of the Society of Petroleum Engineers held in Washington, DC, October 4-7, 1992.
19. Xiao, Y. and Vaziri, H.H., “Import Of Strength Degradation Process In Sand Production Prediction And Management,” U.S. Rock Mechanics Geomechanics Symposium held in San Francisco, California, U.S.A., June 26-29, 2011.
20. 吳政達；謝秉志；范振暉；林再興，利用臨界壓降法預測地下儲氣窖地層出砂之研究，石油鑽採工程，44期，117~123頁，2003年。
21. 楊逸賢，砂岩之峰後力學特性研究，2013年
22. 潘國樑，工程地質通論，2013年。
23. 謝秉志及林再興，利用井測資料估算地層強度之研究，礦冶，第44 卷，第3期，第49-62頁，2000年。