Research on conversion time between lost circulation and overflow for the fractured stratum

Abstract

A new model was established based on the flow model of the drilling fluid in one-dimensional radial fracture to research the influencing factors on conversion time between lost circulation and overflow for multi-pressure system in fractured reservoirs. And the equation of the conversion time between lost circulation and overflow is obtained by solving the mathematical model. The model were validated by reproducing the field data from Sichuan oil field and the simulation results of references. The influences of consistency index, liquidity index, dynamic shear force, drilling fluid density, drilling fluid intrusion depth, pressure of lost circulation layer, crack width, decreased height of annular liquid level, pressure of high-pressure layer were analyzed. Results indicate that conversion time between lost circulation and overflow increases with the increasing consistency index, liquidity index, dynamic shear force, drilling fluid density, drilling fluid intrusion depth, pressure of lost circulation layer. Conversion time between lost circulation and overflow decreases with the increasing crack width, decreased height of annular liquid level, pressure of high-pressure layer. The time interval of “Hang's Mudding-off” operating should be appropriately less than the conversion time between lost circulation and overflow. Under the premise of ensuring wellbore safety, appropriately increasing the consistency index, liquidity index and dynamic shear force of the drilling fluid can effectively increase the conversion time between lost circulation and overflow in large fractured stratum.

Keywords

Fractured stratum / Conversion time / Lost circulation / Overflow

Acknowledgments

The authors gratefully acknowledge the financial support of the National Key R&D Program of China（No. 2018YFC031020201) and the Sichuan Science and Technology Project (2019YFS0045).

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