Pruebas Isocronales De Gas

Learning from Modified Isochronal Test Analysis Middle East Gas well Case Study
A. A. Al-Subaie, B. D. Al-Anazi, A. F. Al-Anazi
PROFESSIONAL PAPER

The natural gas has recently become the main source of energy and determining the optimum production of gas wells is very important for efficient production planning. A modified isochronal test was performed as a tool in evaluating a hydraulicfracturing treatment on a gas well. Pressure test analysis was performed to investigate the success of the treatment. Inflow performance curves, and pressure and production forecast were also performed using diffusivity equation as well as Material Balance equation. The study was conducted on a gas well in a Middle Eastern reservoir. The analysis shows that the hydraulic fracturing treatment on thegas well was successful through an improvement in well productivity. Reservoir properties were also determined from the pressure test and the inflow performance curves were successfully generated and can be used for further study. Key words: isochronal test, hydraulic fracturing, inflow performance curve, absolute open flow

1. INTRODUCTION
The inflow performance can be defined as therelationship between the flow rate and the pressure drop or flow rate and flowing pressure. Figure 1 shows the movement of gas from the reservoir to the well and from the well through the tubing or casing to the surface. The inflow performance depends on reservoir and fluid properties such as permeability and viscosity. Inflow performance determines the well deliverability where the well can deliver onlywhat the reservoir provides. The objectives of inflow performance study are as follows:

1. To determine the flow rate at which a well will produce with a given wellbore geometry and completion (first by natural flow). 2. To determine under what flow conditions a well will cease to produce. This is a function of time as the reservoir deplete. 3. To optimize the well conditions and geometry systemin order to most economically produce the objective flow rate. 4. To analyze each component in the well system to determine if it is restricting the flow rate unnecessarily when compared to the flow capacities of the other system components. In general inflow performance allows quick recognition by the operator's management and engineering staff of means to increase production rates. This is avery important feature of being able to graphically display the wells performance with “production optimization”.

Literature Review:
Predicting the inflow performance of gas wells is a process that has relied almost exclusively on some form of multipoint well testing procedure. The conventional backpressure or flow-after-flow test, isochronal test, and modified isochronal test have been used topredict the deliverability of gas wells. Rawlins and Schellhardt16 presented the back-pressure method of testing gas wells. It is dependent upon the requirement that a series of flow rates and corresponding pressure data be obtained

Fig. 1. Possible pressure losses in complete system.Brown3 Sl. 1. Moguæi pad tlaka u cjelokupnom sistemu, Brown3

NAFTA 60 (7-8) 407-415 (2009)

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A. A.AL-SUBAIE, B. D. AL-ANAZI, A. F. AL-ANAZI

LEARNING FROM MODIFIED ISOCHRONAL TEST...

under stabilized flow conditions. The conventional backpressure equation is given by:
2 qg sc = C( p R 2 - pwf ) n

by the rock and fluid properties. The various flow regimes are discussed with respect to the behaviour of this pressure disturbance.

(1)

2.1. Steady state:
Steady state implies thatpressure does not change with time at any location in the reservoir. This occurs when there is a continuous pressure support such as water drive reservoir, whereby the water influx rate equals the producing rate as shown in figure 2.

These data are plotted on logarithmic coordinates of the difference in the pressures squared versus the flow rate in order to determine the constants, C, and, n....