Pulse Testing Over Long Distances In A High Permeability Reservoir
Authors: McIntosh J.R. , Boggus R.F. , Cockerham P.W. , Hutfilz J.M. 
Published: December 2007

Introduction

In order to more accurately predict reservoir performance in the Ghawar field, an extensive performance in the Ghawar field, an extensive program of reservoir description is underway by program of reservoir description is underway by means of cores, logs and well testing. A logical extension of this effort is to investigate interwell reservoir properties by multiple well transient pressure tests. A series of reservoir pulse tests was conducted and the results pulse tests was conducted and the results indicate that this reservoir description technique is feasible over inter-well distances normally encountered in the developed areas of Ghawar. Observed time lag ranged from 0.37 to 0.60 days and pressure pulse response amplitudes ranged from 0.42 to 1.66 psi.

In past reservoir modeling efforts we have noticed that, in general, significantly higher transmissibilities are required to match pressure history than are deduced from either single well pressure tests or core analysis. One possible pressure tests or core analysis. One possible reason for this could be that the reservoir has anisotropic permeability. The first pulse test series was configured such that we could analyze the results for possible directional permeability. The test area consisted of three permeability. The test area consisted of three pulsed wells forming approximately an equilateral pulsed wells forming approximately an equilateral triangle with an observation well in the center (see Figure 1), and is located in the central part ('Uthmaniyah) of the Ghawar field.

Background

The pulse testing technique described by Johnson, et al, was selected for application in Ghawar field under conditions of high reservoir permeability and wide well spacing. Other similar permeability and wide well spacing. Other similar testing techniques have been developed and are noted or summarized in Reference 3. This reservoir description technique is a special type of interference test in which a sequence of short duration pressure pulses or disturbances are created in a pulsing well by a series of shut-ins and are recorded in a nearby observation well. This series of pulses makes it easier to detect the arrival of the disturbance at the observation well.

Figure 2 depicts schematically the creation of pulses in a producing well by a series of shut-ins. Terminology associated wily the test are indicated. The hypothetical pressure response at an observation well is shown in the lower schematic. Each response to changes in the pulsing well is characterized by two quantities: pulsing well is characterized by two quantities: the pulse Response Amplitude and the Time Lag. The Time Lag is the interval between the end of a pulse in the pulsing well and the point of maximum pulse in the pulsing well and the point of maximum response to that pulse in the observation well. The Response Amplitude is determined in the manner shown in the schematic. Each pulse and inverse (or odd) pulse is characterized in this manner.

The main objectives of using the pulse test were to determine the feasibility of using this technique in Saudi Arabian oil reservoirs which have high transmissibilities and well spacing in excess of one kilometer, and to investigate the possible existence of directional permeability. possible existence of directional permeability. The location for the first pulse test was selected to minimize the effects of wide well spacing and free gas saturation, which are two factors that are unfavorable to successful pulse testing. The test site is shown in Figure 1. The three pulsing wells are located slightly over one kilometer from the central observation well. Reservoir pressure in this area has always been above the saturation pressure of approximately 1900 psi, thus eliminating any presence of a small free gas saturation which would increase reservoir compressibility.

The wells that were pulse-tested produce from the Arab-D reservoir which is the main reservoir in the Ghawar field. The Arab-D consists of a mixture of limestones and dolomites.