Main Evaluation Factors of Fractured Formation Leakage in Bohai Bay Basin

Jiang Shao-long¹*, Zhang Guo-qiang², MU Gui-peng¹, Yuan Ren-guo¹ and Xin Zhao-ling²

Published: March 29, 2022

DOI: 10.55162/MCET.02.026

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Abstract  

In the central area of the Bohai Oilfield including Bozhong block, the geological structure is complex, faults and fractures are extensively developed and the formation is broken. As consequence, there is leakage to some extent in most exploratory wells in Bozhong Block, significantly affecting the drilling efficiency and increasing drilling risks. The problem of well leakage in this block needs to be addressed urgently. For this purpose, the research group firstly researches into the wellbore leakage mechanism, and then establishes a regional leakage pressure prediction model by depiction of the main controlling factors of leakage and preliminarily obtains the following findings: (1) the leakage in Bozhong Block mainly occurs at the depth of 2700-3400m, with Member 2 and Member 3 of Shahejie Formation as the main leakage zones and the fractures and faults as the main leakage passages; (2) the fracture index that can most clearly reflect the well leakage characteristics in Bozhong Block is the fracture evaluation index obtained using the resistivity ratio method, and may be considered as a main controlling factor for evaluation of fractured leakage; (3) according to the statistics on leakage of 22 wells in Bozhong Block, there are nine wells with leakage, totaling 13 leakage points. Based on the statistics and modeling, a leakage pressure prediction model for this block is obtained preliminarily. The research on the leakage mechanism and leakage pressure prediction of fractured formation in Bozhong Block is helpful for reasonable optimization of borehole trajectory, improvement of leakage control of fractured reservoirs, reduction of drilling cost and raising of operation efficiency.