Application of Decline Analysis in Shale Oil Productivity Evaluation and Prediction: A Case Study of Jimsar Shale Oil
Authors: He Si , Ge Hongkui , Zhang Jialiang , Shen Yinghao , Wang Xiaoqiong 
Published: September 2022

ABSTRACT:
Shale oil has become one of the most important unconventional energy sources. Jimsar shale oil reserve is huge and has broad development prospects. In order to understand the production situation and development potential of shale oil in Jimusar, a workflow of decline analysis based on production data was proposed to evaluate productivity and predict production. Taking a single well as an example, this method based on the production data, combined with well and reservoir data, uses conventional Arps decline model, Duong model, flow material balance method (FMB) and typical curve Blasingame to perform decline analysis and predict the expected ultimate recovery (EUR) and original oil-in-place (OOIP). EUR is the weighted average of the above methods, and the weight is calculated by analytic hierarchy process (AHP). According to the AHP, the weights of Harmonic Decline, Exponential Decline, Duong Decline, Blasingame and FMB are 0.285, 0.080, 0.209, 0.213 and 0.213 respectively. OOIP takes the average of Blasingame and FMB prediction results. At the same time, initial decline rate (Di) is calculated to evaluate the well stimulation. Therefore, this paper summarizes and proposes a workflow for shale oil productivity evaluation and prediction:(1) Data collection, collation and import;(2) Decline analysis;(3) Analysis results processing;(4) Comprehensive evaluation of oil well. The results show that the workflow is well applicable to the example well and it is also suitable for other wells in Jimsar. According to the EUR, OOIP and Di calculated by the method, the development value of each well and area can be evaluated and the development plan can be optimized.

1. INTRODUCTION
With the continuous progress of exploration and development technologies such as horizontal drilling and staged fracturing, the reserves of unconventional oil and gas resources have gradually increased. As a typical unconventional hydrocarbon resource, the development of shale oil has been one of the important strategies of the oil industry (Oyekunle,2014). Jimsar shale oil is a typical example of shale oil in continental saline lacustrine basin, with well-controlled reserves of over 1 billion tons and broad development prospects. The study of production decline law is of great significance to the prediction of oilfield production performance and oil production planning (Falcon,2021). There is a great demand for accurate production prediction in unconventional oil and gas developments. Methods including decline curve analysis (DCA), analytical simulation and numerical simulation all have their advantages and disadvantages. Only DCA technology can use readily available production data for rapid prediction with some degree of accuracy (Joshi et al.,2013). Decline analysis is also the preferred method for unconventional well performance prediction and reserve estimation (Artus et al.,2018, Acuna,2021). Compared to traditional well test analysis, it is more convenient and effective, and without shut-in to restore pressure measurement. It can ensure normal production of the oilfield while achieving the purpose of unstable well testing and productivity prediction.