ABSTRACT:

The exploitation of deep oil and gas resources has attracted increased attention. When drilling, a high frequency of lost circulation results from the features of high temperature, high pressure, and high stress, where the temperature is an important factor that cannot be disregarded. The effect of temperature on drilling fluid loss law as well as the influence of temperature difference on fracture initiation, fracture geometry, and fracture extension rate is investigated using a fully coupled Thermal-Hydrological-Mechanical (THM) model built using the finite element method. The simulation results demonstrate that the temperature effect can dramatically lower the lost flow rate. Only when the flow rate is low does temperature dominate the lost fracture extension, which is then divided into the flow-rate dominance stage and temperature dominance stage under high flow rates.

INTRODUCTION

Deep oil and gas resources are characterized by high temperature, high pressure, and high stress, which commonly results in lost circulation incidents while drilling and severely impedes the progress of exploration and development. The optimization of plugging materials and the selection of the plugging method are both heavily influenced by lost fracture size. Currently, scholars use analytical solutions and numerical simulations to predict the lost fracture size.

The analytical solution of lost fracture is mainly based on the theory related to hydraulic fracturing. In 2004, Alberty proposed a linear fracture resolution model to determine the size of a single lost fracture in the classic "Stress Cage" study(Alberty & McLean, 2004). Since then, researchers have increasingly taken into account the analytical model of lost fracture size based on it, which is affected by well slope, stress anisotropy, non-uniform intra-seam pressure distribution, and multiple fractures(Y. Feng & K. E. Gray, 2016; Morita & Fuh, 2012; Shahri et al., 2015; van Oort & Razavi, 2014; Zhang et al., 2016). These models, however, are based on the theory of linear elasticity, and the majority of them disregard the impacts of heat transport.

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