预测页岩气井产量和可采储量泛指数递减模型的建立及应用

Establishment and application of pan exponential decline model for forecasting production rate and recoverable reserves of shale gas wells

随着中国页岩气工业的发展和大量页岩气井的投产,如何有效地预测页岩气井的产量和可采储量已成为油气藏工程的重要课题,也是页岩气资源的生产和管理部门极为关心的问题。由于页岩气是以吸附状态和自由状态分别储存于超致密页岩基质和次生裂缝系统中,而页岩气井在钻井、完井、测井和压裂过程中受到泥浆的多次污染。因此,投产后的页岩气井表现出明显的独立性、差异性和复杂性。再者,由于页岩气井以降压解吸和能量消耗式开采,具有投产即进入递减的特征,因此,产量递减法已成为首选的评价方法。基于陈元千等提出的广义单峰周期预测模型,经简化后得到预测页岩气井产量和可采储量的泛指数递减模型。该模型的递减指数m为0~1。当m=1时为著名的指数递减模型;当m=0.5时可得具有实用价值的0.5型泛指数递减模型。对于具体的非常规气井,在实际预测中,需要利用生产数据通过线性迭代试差法,确定a和c及m值。根据美国宾州Marcellus页岩气藏两口页岩气井生产数据,利用泛指数递减模型,对页岩气井的产量和可采储量进行预测。结果表明,建立的泛指数递减模型是实用有效的。

With the advancement in China’s shale gas industry and the large-scale production of shale gas wells,how to ef⁃fectively forecast the production rate and recoverable reserves of shale gas wells and has become a crucial subject of oil and gas reservoir engineering.It is also a matter of great concern to shale gas production and management departments.As shale gas is stored in the ultra-tight shale matrix and the secondary fracture system in the adsorption state and the free gas state,respectively,it can be polluted by mud during the drilling,completion,logging,and fracturing.Therefore,the shale gas wells that have been put into production show obvious independence,diversity,and complexity.More importantly,shale gas wells are brought into production by desorption after pressure drops and energy consumption featured by the decreasing production at the moment it starts.Consequently,the production decline method has become the first choice for evaluation.In this paper,the generalized single peak cycle model proposed by Chen Yuanqian et al.is simplified into a pan exponential decline model(PEDM)that can forecast the production rate and recoverable reserves of shale gas wells.The decline expo⁃nent m ranges from 0 to 1.At m=1,it is the famous exponential decline model.At m=0.5,it is the 0.5-PEDM of practical value. For specific unconventional shale gas wells,it is necessary to use production data to determine the values of a,c,andm by linear iterative trial and error method in actual forecasting. The application of production data from two wells in theMarcellus shale gas reservoir,Pennsylvania,the US,elicits the effectiveness of the PEDM in forecasting the production rateand recoverable reserves of shale gas wells.