Recently, a variety model/method to evaluate shale fracability and shale oil mobility have been developed, however, few studies take accounts for the synergic effects of fracability and oil mobility, and provide quantitative pre-evaluation of post-fracturing recoverability in shale oil reservoir. In addition, lamellation-type shale oil reservoir in China is mud-grade pure shale with large amounts of laminae developed, the existing evaluation models could result in great errors. Hence, it is of great value to develop new quantitative pre-evaluation method to more accurately evaluate the post-fracturing recoverability in shale oil reservoir.
For this purpose, the various factors affecting lamellation-type shale reservoir fracability and oil mobility are analyzed, of which dataset is obtained by various well logging and core experiments, including ϕe, lamination density, TOC, So, Ro, S1, OSI, αp, BI, Pf and Ds. Followed by, a new improved analytic-hierarchy-model integrating with entropy weight method is developed to determine the influence weights of the above factors. Then a novel quantitative pre-evaluation model is established to forecast the post-fracturing recoverability of shale oil well completed with multi-stage fracturing in shale oil reservoir, and moreover the quantitative pre-evaluation results are verified by the post-fracturing production performance using the unconventional rate-transient analysis (RTA) method.
The new analytic-hierarchy-quantitative (AHQ) pre-evaluation method compensates for the inability of that most available methods lack of the synergic effects of fracability and oil mobility. For the target lamellation-type shale oil well in China, the improved AHP results reveal the contribution of the factors affecting shale oil well post-fracturing recoverability: laminae, S1 and OSI contribute by 58.8% in total; while the eight other factors contribute by 41.2%. It is also observed that the lower three layers of the target well have higher post-fracturing recoverability, with average 54% above other layers. Moreover, the AHQ pre-evaluation method is verified by the reservoir/fracture characterization results using RTA method based on on-site well production data within 10% in error.
For the first time, both the shale fracability and shale oil mobility are coupled into a new evaluation parameter entitled by post-fracturing recoverability in shale oil reservoir, and the new AHQ pre-evaluation method is developed further. The practical significance of this work is to provide critical technical reference for more accurate pre-evaluation of fracturing production potential and optimization of reservoir development program design in shale oil.
