- 期刊
利用岩石力學評估鐵砧山儲氣窖鑽水平注產氣井出砂之可能性
Sand Production Prediction for TCS Horizontal Well －From Rock Mechanics Point of View
摘要
中油公司為穩定供應國內電力公司天然氣發電與天然氣市場成長需求，早在民國76年(1987)台探總處即將鐵砧山氣田規劃為地下儲氣窖，以調節市場尖、離峰之用氣量。因國內天然氣市場成長迅速，台探總處除了於88年(1999)新鑽六口注產氣井專門做為地下儲氣窖使用之外，更規劃於未來再鑽數口水平注產氣井以擴充注產氣井以擴充注產氣能力。國內尚無鑽水平井之經驗，對於在鑽井過程中是否會發生井壁崩塌？以及生產時會不會出砂？需採用何種完井方式？等問題均有待進一步研究。 出砂與否其實最基本的控制因素乃在於岩層的力學性質及其所受之應力狀態，因此本研究以實驗的方式，採實際的岩心進行一系列的岩石三軸試驗，實測其力學特性參數，包括內聚力、內磨擦角、楊氏係數及卜松比等，再將這些實測所得之參數，分別利用S. Ong et al.等人在SPE上發表的張力破壞出砂預測模型以及Coates & Denoo (1981)所發表之井孔附近剪力破壞預測模型，預測儲氣層在井孔附近因受剪力破壞而導致出砂之可能性。同時更利用商業化之出砂預測分析軟體『STABView』，針對未來注儲及生產時是否會出砂等狀況進行模擬計算。 模擬結果顯示，因為目前之地層壓力已經從原始的3915 Psi下降至約2500 Psi，岩層所受到之有效應力較原始狀態高出約1400 Psi，水平孔段在未來注產操作時可能會有受剪力破壞而出砂的問題。根據分析結果，水平井所能承受之生產差壓降(Drawdown Pressure)遠低於直井或定向井，出砂的可能性相當高，必須採取適當之完井方式以達到長久而且有效之防砂作用。
並列摘要
In order to stably serve the natural gas consumption of the gas-fired power plants as well as the increasing market, Taiwan Petroleum Exploration Division (TPED) of CPC started planning to convert the TCS gas field into an underground storage since 1987. The underground storage will act to accommodate the discrepancy between the peak and off-peak hour natural gas consumption by injecting, storing and producing the gasified LNG. Because of the rapid growth of the natural gas market, TPED drilled 6 I/W wells in 1999 to serve the market and is planning to drill several horizontal wells in the near future to up-scale the I/W capacity to a rate of 660 ton/hr or 1080 ton/hr, depending on the market demand. No horizontal well has ever been drilled in Taiwan, therefore, it is necessary to perform studies of wellbore instability evaluation, sand production prediction, what type of completion to be used and so on. The basic factors that control the sand production are the mechanical characteristics of the rocks and the stress state that the rocks are subject to. A series of triaxial tests using real core plugs were conducted to obtain the main mechanical properties such as cohesion, internal angel of friction, Young’s modulus and Poisson’s ratio. These parameters were then used as input data for a Tensile Failure Critical Drawdown Pressure predicting model, presented by S. Ong et al. (2000) in SPE paper, and for a Compressive Failure predicting model proposed by Coates & Denoo (1981), to perform the sand production prediction. In addition, a commercialized sand production prediction software, STABView, was also used for the same purpose. The results obtained from different methods were then compared and analyzed. The results reveal that because the formation pressure has depleted from its original pressure of 3915 Psi down to the present value of some 2500 Psi, the decreased some 1400 Psi effective stress is now taken by the rock, leading to that compressive failure is very likely to occur along the horizontal section, especially those weak portions, in the future operation, and sand production is the result. According to the calculation, the sanding drawdown pressure of horizontal well is much less than that of vertical well. It is highly possible to have severe sand production problem, and thus long lasting completion that can successfully prevent sand production is surely needed.