Until recently, cement simulation programs have been difficult to use, required large computer systems, and occasionally yielded results that were difficult to understand. Often the data input task was cumbersome enough to limit usage of these simulators. With the advent of Graphical User Interfaces (GUIs), even the most sophisticated simulator can be easy to use. With the wide variety of today's PC Graphics packages, complicated results can be made comprehensible through visual displays. This paper describes a technically advanced PC-based primary cement job simulator illustrating how a simulator can be sophisticated and easy to use at the same time. The simulator description includes recent enhancements, such as the capability to utilize temperature-dependent rheology and Critical Reynolds Number when calculating frictional losses.

Access to an effective primary cement job simulator is an important part of a sound cementing program. A simulator provides the designer with a tool that can be used to fine-tune job designs, helping to obtain the safe completion of all planned cement jobs.

A truly user friendly program will require minimal training, reduce design time, and be used more often. A GUI and extensive error checking routines are required if a complex, technically advanced simulator is to be considered user friendly. The PC platform was chosen to allow widespread use this software.

User Interface

The man-machine interface (MMI) plays an important role in the ultimate success or failure of any piece of software. For this reason a GUI was chosen for use as the MMI. By providing a GUI the complex task of transferring, from the user to the computer, the information required by mis simulator is simplified.

In addition to simplifying the transfer of information, a good interface helps in seeing that the information transferred is the information mat is actually required. The subject GUI accomplishes this task with extensive error and range checking features. Any problems or unusual values are reported to the user through a series of warning and/or error messages written in plain English. Uncaught, these input errors might result in non-english compiler-generated error messages.

Simulator

In common with other primary cement simulators is the capability of pumping various fluids at different rates through changing tubular and annular diameters. Like other sophisticated simulators, this model can also handle freefall, hookload calculations, foamed fluids, and shutdowns. This simulator's additional features include:

  • *

    Automatic reduction of pump rate at any point(s) in the job in an effort to reduce equivalent circulating density (ECD) to a safe value

  • *

    Continual recalculation of an increased or decreased viscosity based on a changing, depth-dependent temperature

  • *

    Capability to input a unique casing and annular temperature profile directly from a temperature simulator

  • *

    Dynamic calculation of the Critical Reynolds Number to determine whether a fluid is actually in turbulent flow or not

  • *

    Capability to adjust backpressure during the job

Dynamic Rheology

Most fluids thin when they are heated and thicken when they cool.1  Previous simulators used a constant rheology (normally measured at surface, BHCT, or some midpoint value) throughout the wellbore. In deep wells with a substantial bottomhole temperature, temperature thinning fluids will exert considerably different frictional pressures at different depths. If a single rheology profile is used across the entire wellbore length, a significant error may be induced. This simulator breaks the wellbore down into many "constant rheology" segments, continuously recalculating the viscosity for each segment.

Temperature Profiles

To provide temperature/depth information to the rheology model, this simulator provides considerable flexibility. The user can choose to use a single straight line to describe both the annulus and casing, separate straight lines for heating down the casing and cooling up the annulus, or a temperature vs. depth profile from a temperature simulator.

Critical Reynolds Number

Instead of using the standard value of 3000 to determine whether to use turbulent or laminar friction correlations, this simulator continuously recalculates a Critical Reynolds Number2  for each fluid in each geometry. Reynolds Number and the Critical Reynolds Number are compared to determine the proper flow regime.

  1. A user friendly primary cement job simulator has been developed and described.

  2. Temperature-dependent rheological calculations improve the accuracy of friction calculations thus improving overall pressure predictions.

  3. Because the simulator is PC based, it can be run by any PC-literate user.

This paper was selected for presentation by an SPE Program Committee following review of information contained in an abstract submitted by the author(s). Contents of the paper, as presented, have not been reviewed by the Society of Petroleum Engineers and are subject to correction by the author(s). The material, as presented, does not necessarily reflect any position of the Society of Petroleum Engineers, its officers, or members. Papers presented at SPE meetings are subject to publication review by Editorial Committees of the Society of Petroleum Engineers. Permission to copy is restricted to an abstract of not more than 300 words. Illustrations may not be copied. The abstract should contain conspicuous acknowledgment of where and by whom the paper is presented. Write Librarian, SPE, P.O. Box 833836, Richardson, TX 75083-3836, U.S.A. Telex, 163245 SPEUT.

Ravi
,
K.M.
and
Sutton
,
D.L.
: "
New Rheological Correlations for Cement Slurries as a Function of Temperature
,"
paper SPE 20449 presented at the 1990 Annual Fall Technical Conference and Exhibition
,
New Orleans,
Sept. 23-26
.
Shah
,
S.N.
and
Sutton
,
D.L.
: "
New Friction Correlation for Cements From Pipe and Rotational Viscometer Data
,"
paper SPE 19539 presented at the 1989 Annual Fall Technical Conference and Exhibition
,
San Antonio,
Oct. 8-11
.