Utilizing A Field Computer System During Cementing To Help Avoid Costly Workovers
Authors: Purvis Don , Gregory Garth 
Published: March 2010

The need for costly workover operations can be reduced by accurately monitoring and modelling cementing operations with a field computer system.

This paper shows how realtime computer monitoring is used to detect downhole problems prior to and during cementing, increase quality control, maintain proper flow regimes and present downhole equivalent circulating densities to assist in avoiding lost circulation and/or influx. A description of the application of A.P.I. Specification 10 (Appendix J)(1) by this realtime model is presented.

Introduction

A great deal of work has been done by the industry to increase our ability to model a cementing operation. The value of realtime job monitoring has been presented(2). Methods for on-site diagnosis(3), and post-job analysis(4) have been presented.

With the recent advances in personal computer technology it is now possible and more economically feasible to apply a realtime computer model to cementing treatments.

This technology has been applied on a large number of treatments and has helped improve the probability of success. By monitoring and analyzing the rate of pumping, slurry density, and well head pressure with a computer system, the quality control of a cementing operation is greatly enhanced. The rate of returns and return density are monitored when possible. This allows the actual downhole conditions to be more accurately modelled and potential problems detected.

The flow regime of mud, spacer and cement are calculated by tracking the slurry density, rheology and velocity throughout the annulus. Surface adjustments have then been made to keep the respective fluids in a flow regime that will be most beneficial for mud removal and cement placement.

Pore and fracture pressures throughout the open hole region are convened to equivalent densities. By overlaying a graphic representation of these parameters vs depth with the calculated equivalent circulating density, an equivalent density window is presented. This information can be used to adjust the rate to help avoid influx from the formation or lost circulation.

The procedure for calculating frictional pressure outlined in the American Petroleum Institute Specification 10 Appendix J(1) was followed in the program development.

Description of Computer Monitoring System

The computer monitoring system used consists of transducers on the pumping and return lines, a data acquisition system and an MS-DOS-based computer with various peripherals (Fig. 1). This system is described in the Appendix. The computer uses information from the transducers to calculate several screens of information. These screens are described below.

Wellbore and Data Display

The wellbore diagram and monitored data displayed across the top of Figure 2 are the same for each of the screens. The wellbore diagram displays the respective position of each fluid in the wellbore. This is updated continuously as a function of the profile calculations. The data display is updated every one to two seconds.

Flow Regime

This screen displays a continuously updated plot of equivalent Reynold's Number vs depth (Fig. 2). The line marked ‘laminar’ represents the maximum Reynold's Number for the fluid to be in laminar flow.