The empirical range of deliverability ratio between horizontal well and vertical well is usually regarded as 2–5. But actually, this range is too large and the real ratio may not be within it. To quantify the deliverability ratio relationship between horizontal well and vertical well more accurate, the deliverability ratio relationship is derived based on modified Joshi's horizontal well deliverability formula and vertical well deliverability formula. Then as for different horizontal well lengths with known parameters of the pay zone in the vertical well where the horizontal well locates, corresponding deliverability ratios can be obtained. And then the horizontal well deliverability can be predicted by multiplying the known appraisal well (vertical well) deliverability and the deliverability ratio.

Sensitivity analysis between the deliverability ratio and relevant parameters is done by using pay zone, fluid and well parameters of Q oilfield of China Bohai Bay. The results show that as for different parameter combinations, the deliverability ratio can be within or without the range of 2–5; skin factor and off-center distance have little effect on the deliverability ratio, while as horizontal length increases, permeability anisotropy factor increases and pay thickness increases as well as drainage radius decreases, the deliverability ratio will decrease obviously. These regularities coincide with actual development regularity, which verifies the accuracy of the proposed method.

The proposed method quantifies the deliverability ratio range between horizontal well and vertical well, and increases prediction accuracy of horizontal well deliverability; therefore it is of great practicability, especially for early stage reservoir development.

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