Comparison of Steady State and Transient Analysis Dynamic Kill Models for Prediction of Pumping Requirements
Authors: Abel L.W. , Shackelford D.W. 
Published: December 2007

The purpose of this paper is to compare three methods of calculating dynamic kill requirements for a blowout well. The use of computers, especially desktop PC's, has made complex analytical solutions more readily available in solving engineering problems. The power and capability of the computer has increased dramatically in recent years, as has the analytical complexity and effectiveness of engineering solutions. This paper compares three methods that have been used successfully in the field to dynamically kill blowout wells, either from relief wells or through a tubular conduit in the well. The methods to be compared and discussed in this paper are:–Pure friction dynamic kill–Steady state two-phase flow analysis–Transient two-phase flow analysis

To make the comparisons useful to the reader, each of these analytical methods has been applied to the same type of well with identical reservoir conditions and characteristics. The conclusions show that the kill requirements can be estimated by using simplified models, but to more accurately estimate pumping schedules (i.e. volumes and pumping times) a complex model and analysis is required. A tabular presentation is used to show the value and limitations of each method.

Introduction

This paper compares dynamic kill calculation methods available to estimate kill requirements during a blowout. Three methods were used in this comparison:pure friction,steady state two-phase andtransient two-phase models.

For each analysis, the same reservoir and well geometry were used so that the comparisons would yield meaningful results. The definitions of each method are as follows:–Pure friction - The friction losses generated by fluid flow plus hydrostatic pressure combine to exert a pressure against the reservoir. The design criteria is that the model estimates the kill rate that will produce a pressure at the reservoir that is greater than or equal to the static reservoir pressure.–Steady state two-phase - The friction resulting from a steady state two-phase flow is such that the compressibility and other important non-Newtonian behavior of the fluid mix is accounted for in estimating the reservoir IPR (Inflow Performance Relationship) effects in determining the minimum kill rate requirements–Transient two-phase - This model uses two- phase calculations for frictional losses and phase behavior, but also estimates the time dependency relationships of the reservoir (IPR, changing fluid compositions, etc.) and the fluids in the blowout flow path. This model is useful in determining real-time pumping schedules for kill operations.

PURE FRICTION MODEL

The pure friction model uses friction generated by pipe flow through the geometry of the blowout in the wellbore to establish an equilibrium where the well cannot produce. When this equilibrium is established the well is controlled. The combination of pressure losses and hydrostatic column overcome the reservoir pressure. The basic assumptions are shown in Figure 1. The major assumptions are that the wellbore is filled with kill fluid and the sum of all the pressure losses and hydrostatic pressures combine to exert a pressure greater than the static reservoir pressure.

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