Application of the probability method to undeveloped EUR assessment of shale gas: A case study on one mature shale gas block in North America

Scale shale gas development in China is currently in its initial stage, and the study on the assessment methods for estimated ultimate recovery (EUR) of shale gas is still in the stage of continuous accumulation and improvement. In particular, the application of probability method with higher estimate accuracy in shale gas reserves assessment is limited. In this paper, shale gas EUR assessment methods were analyzed and evaluated. Then, the modified hyperbolic decline model was adopted to predict the EUR of in-service wells in one mature shale gas block in North America and its probability distribution was provided. Based on the above mentioned results, the undeveloped EUR of new wells was simulated using probability method, and the rational utilization and application effects of probability method were expounded based on four scenarios, i.e., target probability, project risk, project comparison and more rational EUR assessment. And the following research results were obtained. First, with the advancing of shale gas development project, the number of production wells increases and the exploitation technologies get mature. Thus, the analogy well groups whose rational confidence satisfies the requirement of probability method can be established so as to provide the basis for undeveloped EUR assessment using probability method. Second, the undeveloped EUR of shale gas project is partially affected by the sum of wells. The decrease of well quantity in the future can increase the uncertainty of undeveloped EUR, and on the contrary, the increase of well quantity can reduce the uncertainty of undeveloped EUR. Third, the probability method has the possibility to describe the undeveloped EUR of different levels quantitatively and can reflect project uncertainty and risk quantitatively. And it can provide the basis for project identification and decision making through project comparison from the aspects of uncertainty and risk. In conclusion, the probability method is a more rational and reliable choice for undeveloped EUR assessment of shale gas projects as the number of shale gas wells increases and the exploitation technologies are developed further. © 2018, Natural Gas Industry Journal Agency. All right reserved.