1.3.1. Introduction

Radiotracer applications for interwell communication studies were carried out in two oilfields in Pakistan. The study area consists of two oilfields (oilfield 1 and oilfield 2) and is shown in Fig. 58.

1.3.2. Tracer test in oilfield 1

The study is being carried out in the Fimkassar oilfield, which is operated by the Oil and Gas Development Co. Ltd. This oilfield is located in the Potowar Basin, about 100 km southwest of Islamabad. The field has two production wells (wells 1 and 2) and the third well (well 3) is used as an injection well for water flooding. A fourth well was drilled but it was ‘dry’ and was capped. The pattern and the location of the wells are shown in Fig. 59.

Objectives

The main objectives of the study were to:

• Determine breakthrough time between injection and production wells;

• Assess the contribution of injected water towards the production well and investigate the presence of quick channelling between the injection and production wells;

• Determine the swept volume of the reservoir by injected water;

• Assess the efficiency of injected fluid to increase the reservoir pressure;

• Assess the relative contributions of injected water and formation water in the produced water.

Monthly sampling of producer wells and the injection well was carried out and samples were analysed for tritium (3H) and stable isotopes (2H, 18O) using liquid scintillation counting and isotope ratio mass spectrometry, respectively. Radiotracer and stable isotope data were processed and analysed and these data are displayed in Figs 60 and 61.

The work related to this oilfield is complete and the results are as follows:

• Breakthrough time is 252 d.

• Water produced in well 1 has an 85% contribution of fresh injected water.

Inter-Well Tracer Test (Fimkassar Oilfield, Pakistan)

Time after Radiotracer Injection {Days)

FIG. 60. Tracer response curve and tracer recovery (Fimkassar oilfield).

• Mean residence time of tracer (water) is 1367 d.

• Mean injected water volume is 2 497 864 m3.

• Mean produced water volume is 460 711 m3.

• Maximum and mean velocities of injected water are 10.3 m/d and 1.9 m/d, respectively.

• Tracer recovery is ~69%.

Considering a mean produced water volume of 460 711 m3 and 69% recovery of radiotracer from well 1, the mean swept volume is determined as 317 891 m3. This is the average volume of the reservoir swept by injected water.

• After initial reduction in breakthrough time, the injection water has swept a large volume and there appears to be no channels connecting the injection well and production well 1.

• No injected tracer was detected in well 2.

• The tracer response shows that the water flood regime was not managed properly in the initial stages that changed the hydrodynamics of the reservoir and affected the production.

• The water in the formations is meteoric water, recharged from northern parts of the country.