Reservoir Engineering 2 Course (1st Ed.)

1. Conning Vertical Well:A. Critical Rate Correlations

B. Breakthrough Time

C. Breakthrough Performance

1. Coning In Horizontal Wells

2. Horizontal Well Breakthrough Time

horizontal well technology

The applications of horizontal well technology in developing hydrocarbon reservoirs have been widely used in recent years. One of the main objectives of using this technology is to

improve hydrocarbon recovery from water and/or gas-cap drive reservoirs.

The advantages of using a horizontal well over a conventional vertical well are their larger capacity to produce oil at the same drawdown and a longer breakthrough time at a given production rate.

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Coning problem calculations in horizontal wellsMany correlations to predict coning behavior in

horizontal wells are available in the literature. Joshi (1991) provides a detailed treatment of the coning

problem in horizontal wells.

As in vertical wells, the coning problem in horizontal wells involves the following calculations:Determination of the critical flow rate

Breakthrough time predictions

Well performance calculations after breakthrough

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Horizontal Well Critical Rate Correlations: Chaperson’s MethodChaperson (1986) provides a simple and practical

estimate or the critical rate under steady-state or pseudosteady-state flowing conditions for an isotropic formation.Water coning

Gas Coning

The above two equations are applicable under the following constraint:

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Horizontal Well Critical Rate: Chaperson’s Method (Cont.)Where

Db = distance between the WOC and the horizontal wellDt = distance between the GOC and the horizontal well Qoc = critical oil rate, STB/day ρ = density, lb/ft3kh = horizontal permeability, mdh = oil column thickness, ftye = half distance between two lines of horizontal wells(half drainage length perpendicular to the horizontal well)L = length of the horizontal wellq*c = dimensionless function

Joshi (1991) correlated the dimensionless function F with the parameter α″:

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Horizontal Well Critical Rate: Efros’ MethodEfros (1963) proposed a critical flow rate

correlation that is based on the assumption that the critical rate is nearly independent of drainage radius.

The correlation does not account for the effect of the vertical permeability.

Water coning

Gas coning

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Horizontal Well Critical Rate: Karcher’s MethodKarcher (1986) proposed a correlation that

produces a critical oil flow rate value similar to that of Efros’ equation. Again, the correlation does not account for the vertical

permeability.

Water coning

Gas coning

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Horizontal Well Breakthrough Time;The Ozkan-Raghavan MethodOzkan and Raghavan (1988) proposed

a theoretical correlation for calculating time to breakthrough in a bottom-water-drive reservoir. They introduced

the following dimensionless parameters:

L = well length, ftDb = distance between WOC and horizontal wellH = formation thickness, ftkv = vertical permeability, mdkh = horizontal permeability, md

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Horizontal Well Breakthrough Time;The Ozkan-Raghavan Method (Cont.)Ozkan and Raghavan expressed the water breakthrough

time by the following equation:

with the parameter fd as defined by:

tBT = time to breakthrough, days Kv, kh = vertical, horizontal permeability, mdφ = porosity, fractionSwc = connate water saturation, fractionSor = residual oil saturation, fractionQo = oil flow rate, STB/dayEs = sweep efficiency, dimensionless

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Sweep efficiency for horizontal and vertical wellsOzkan and

Raghavan graphically correlated the sweep efficiency with the dimensionless well length LD and dimensionless vertical distance ZWD as shown

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1. Ahmed, T. (2010). Reservoir engineering handbook (Gulf Professional Publishing). Chapter 9

1. Introduction

2. Classification Of Aquifers

3. Recognition Of Natural Water Influx