Scale-Model Displacement Studies To Predict Flow Behavior During Cementing
Authors: Garvin Tom , Slagle Knox A. 
Published: December 2007

Tests were conducted in model wellbores at lower laminar and turbulent flow to determine the influence of relative mud-cement weights and yield values upon displacement efficiency. Fluid properties were examined in both a model and a rotational viscometer and the results were compared so that additional scale-model values could be predicted.

Introduction

Several noteworthy publications written before 1960 apply either directly or indirectly to the problems in fluid flow with which we are concerned here. Among them are the Babbitt and Caldwell report of experiments with sludges and the Metzner and Reed work with the Power Law model for fluid-flow calculations. Weltmann and Green describe the phenomenon of thixotropy. Of the many good examinations in the geometries of fluid flow, two of special interest are those from Piercy et al. and Melrose et al. that consider annular configurations. Howard and Clark applied the known technology to the process of oil-well cementing in their experiments. Although it appeared that the problems were alleviated, cementing difficulties continue.

In more recent work, the techniques of nonNewtonian rheology have been applied to real fluid systems, and the limitations of the mathematical models frequently used for generalized calculations have been explored. Ritter and Batycky and Perkins and Turner have applied the concept of thixotropy to improve pipeline design for handling rheologically complex fluids. McLean et al. and others have explored the variation of geometric factors and have evaluated the analytical techniques for solving problems considering this variable. problems considering this variable. The work discussed here seeks to determine how relative mud-cement density and yield values influence displacement efficiency during lower laminar flow and turbulent-flow cementing operations. Mud was displaced by cement at different flow rates from the centralized annulus of a 1-in. pipe in a series of 2.5-in.-ID cardboard tubes. The annular flow rates were chosen to approximate the shear rates of 50, 100, and 200 rpm in a rotational viscometer. A shear rate of 1,300 sec-1 was chosen for turbulent flow.

The dependency of yield value on quiescent time and load rate was examined in

viscometer, a pipe, and a model, and the results were compared for prediction of additional values from viscometer data.

Cardboard tubes were selected to represent the wellbore in these experiments because they will absorb water from the mud and permit a filter cake to form; and to a reasonable extent one can control the thickness of the filter cake by controlling the time that the system is wetted with water before the mud is introduced. The models were designed with the bottom end of the pipe closed so that circulation was through six ports whose total cross-sectional area equalled the area inside the pipe. These ports were located 6 in. from bottom and phased 60 apart.

Future investigations using the methods reported here are expected to include an evaluation of simulated washouts of several shapes and sizes as well as a study of the effect of eccentric rather than concentric location of the pipe.

JPT

P. 1081