Abstract

There is a need for determining temperature profiles in and around a wellbore during drilling profiles in and around a wellbore during drilling phases. A computer model has been developed. phases. A computer model has been developed. To take into account an evolutive geometry at the level of the tool, an adaptive grid refinement was used; it ensures a better physical representation. The unknowns are the temperatures at the center of each grid block and of each interface. The non-linear equations are discretised in finite-difference fully implicit scheme and solved by the Newton's method.

Complex rheological models are used to improve fluid mechanics' representation. At any location and time, the flow nature is determines and then pressure losses and convective heat transfer coefficients are calculated. Energy source terms are function of location and time.

Any flow history and drilling sequence nay be simulated. Typical drilling sequences are presented. This model has been used in order to design mud and drilling programs to ensure a better hole stability.

Introduction

Drilling aspects such as rock borability, borehole wall instability have been studied from the rock mechanics point of view. From this research arises a need for a better knowledge of the temperature distribution in and around wellbores during drilling operations. After an extensive literature survey and software databank consulting, it appeared necessary to develop a new computer model, with some characteristics similar to the models already described by several authors, but also with additional features which make it original and more powerful.

Marshall and Bentsen described the last published model and one should refer to their literature survey on the topic. Most of the features of the present model have been taken from their paper. This present paper describes first the original numerical scheme and algorithms, taking also into account an evolutive geometry. The second part of the paper describes the additional features of the part of the paper describes the additional features of the model from the physical point of view.

The third and most important part of the paper is devoted to the use of the model in the practice of field temperature data interpretation. Even though this work is not yet completed, it seemed important to draw conclusions and propose recommendations to improve surface and MWD temperatures interpretation.

NUMERICAL FORMULATIONS
General Presentation

In order to simulate the evolution of temperatures in and around a wellbore during drilling phases, the model had to take into account several phases, the model had to take into account several features

  • an evolutive geometry at the level of the tool;

  • non-linear heat transfers in the drilling fluid or in the mud;

  • fast changing operating conditions;

  • heat source terms generated by pressure losses and rotational energy.

Equations of the Model

The first equation is the conservation of energy:

H(Q+Q)=0
(1) t−f−c
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